QString 类

QString class provides a Unicode character string. 更多...

 Header: #include qmake: QT += core

公共类型

 class Null typedef ConstIterator typedef Iterator enum NormalizationForm { NormalizationForm_D, NormalizationForm_C, NormalizationForm_KD, NormalizationForm_KC } enum SectionFlag { SectionDefault, SectionSkipEmpty, SectionIncludeLeadingSep, SectionIncludeTrailingSep, SectionCaseInsensitiveSeps } flags SectionFlags enum SplitBehavior { KeepEmptyParts, SkipEmptyParts } typedef const_iterator typedef const_pointer typedef const_reference typedef const_reverse_iterator typedef difference_type typedef iterator typedef pointer typedef reference typedef reverse_iterator typedef size_type typedef value_type

公共函数

 QString () QString (const QChar * unicode , int size = -1) QString (QChar ch ) QString (int size , QChar ch ) QString (QLatin1String str ) QString (const QString & other ) QString (QString && other ) QString (const char * str ) QString (const QByteArray & ba ) ~QString () QString & append (const QString & str ) QString & append (const QChar * str , int len ) QString & append (QChar ch ) QString & append (const QStringRef & reference ) QString & append (QLatin1String str ) QString & append (const char * str ) QString & append (const QByteArray & ba ) QString arg (const QString & a , int fieldWidth = 0, QChar fillChar = QLatin1Char( ' ' )) const QString arg (qulonglong a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const QString arg (long a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const QString arg (ulong a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const QString arg (int a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const QString arg (uint a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const QString arg (short a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const QString arg (ushort a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const QString arg (double a , int fieldWidth = 0, char format = 'g', int precision = -1, QChar fillChar = QLatin1Char( ' ' )) const QString arg (char a , int fieldWidth = 0, QChar fillChar = QLatin1Char( ' ' )) const QString arg (QChar a , int fieldWidth = 0, QChar fillChar = QLatin1Char( ' ' )) const QString arg (qlonglong a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const QString arg (const QString & a1 , const QString & a2 ) const QString arg (const QString & a1 , const QString & a2 , const QString & a3 ) const QString arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 ) const QString arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 , const QString & a5 ) const QString arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 , const QString & a5 , const QString & a6 ) const QString arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 , const QString & a5 , const QString & a6 , const QString & a7 ) const QString arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 , const QString & a5 , const QString & a6 , const QString & a7 , const QString & a8 ) const QString arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 , const QString & a5 , const QString & a6 , const QString & a7 , const QString & a8 , const QString & a9 ) const const QChar at (int position ) const iterator begin () const_iterator begin () const int capacity () const const_iterator cbegin () const const_iterator cend () const void chop (int n ) void clear () int compare (QLatin1String other , Qt::CaseSensitivity cs = Qt::CaseSensitive) const int compare (const QString & other , Qt::CaseSensitivity cs = Qt::CaseSensitive) const int compare (const QStringRef & ref , Qt::CaseSensitivity cs = Qt::CaseSensitive) const const_iterator constBegin () const const QChar * constData () const const_iterator constEnd () const bool contains (const QString & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const bool contains (QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive) const bool contains (QLatin1String str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const bool contains (const QStringRef & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const bool contains (const QRegExp & rx ) const bool contains (QRegExp & rx ) const bool contains (const QRegularExpression & re ) const bool contains (const QRegularExpression & re , QRegularExpressionMatch * match ) const int count (const QString & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const int count (QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive) const int count () const int count (const QStringRef & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const int count (const QRegExp & rx ) const int count (const QRegularExpression & re ) const const_reverse_iterator crbegin () const const_reverse_iterator crend () const QChar * data () const QChar * data () const iterator end () const_iterator end () const bool endsWith (const QString & s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const bool endsWith (const QStringRef & s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const bool endsWith (QLatin1String s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const bool endsWith (QChar c , Qt::CaseSensitivity cs = Qt::CaseSensitive) const QString & fill (QChar ch , int size = -1) int indexOf (const QString & str , int from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const int indexOf (QChar ch , int from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const int indexOf (QLatin1String str , int from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const int indexOf (const QStringRef & str , int from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const int indexOf (const QRegExp & rx , int from = 0) const int indexOf (QRegExp & rx , int from = 0) const int indexOf (const QRegularExpression & re , int from = 0) const int indexOf (const QRegularExpression & re , int from , QRegularExpressionMatch * rmatch ) const QString & insert (int position , const QString & str ) QString & insert (int position , const QChar * unicode , int size ) QString & insert (int position , QChar ch ) QString & insert (int position , const QStringRef & str ) QString & insert (int position , QLatin1String str ) QString & insert (int position , const char * str ) QString & insert (int position , const QByteArray & str ) bool isEmpty () const bool isNull () const bool isRightToLeft () const int lastIndexOf (const QString & str , int from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const int lastIndexOf (QChar ch , int from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const int lastIndexOf (QLatin1String str , int from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const int lastIndexOf (const QStringRef & str , int from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const int lastIndexOf (const QRegExp & rx , int from = -1) const int lastIndexOf (QRegExp & rx , int from = -1) const int lastIndexOf (const QRegularExpression & re , int from = -1) const int lastIndexOf (const QRegularExpression & re , int from , QRegularExpressionMatch * rmatch ) const QString left (int n ) const QString leftJustified (int width , QChar fill = QLatin1Char( ' ' ), bool truncate = false) const QStringRef leftRef (int n ) const int length () const int localeAwareCompare (const QString & other ) const int localeAwareCompare (const QStringRef & other ) const QString mid (int position , int n = -1) const QStringRef midRef (int position , int n = -1) const QString normalized (NormalizationForm mode , QChar::UnicodeVersion version = QChar::Unicode_Unassigned) const QString & prepend (const QString & str ) QString & prepend (const QChar * str , int len ) QString & prepend (QChar ch ) QString & prepend (const QStringRef & str ) QString & prepend (QLatin1String str ) QString & prepend (const char * str ) QString & prepend (const QByteArray & ba ) void push_back (const QString & other ) void push_back (QChar ch ) void push_front (const QString & other ) void push_front (QChar ch ) reverse_iterator rbegin () const_reverse_iterator rbegin () const QString & remove (int position , int n ) QString & remove (QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive) QString & remove (const QString & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) QString & remove (const QRegExp & rx ) QString & remove (const QRegularExpression & re ) reverse_iterator rend () const_reverse_iterator rend () const QString repeated (int times ) const QString & replace (int position , int n , const QString & after ) QString & replace (int position , int n , const QChar * unicode , int size ) QString & replace (int position , int n , QChar after ) QString & replace (QChar before , QChar after , Qt::CaseSensitivity cs = Qt::CaseSensitive) QString & replace (const QChar * before , int blen , const QChar * after , int alen , Qt::CaseSensitivity cs = Qt::CaseSensitive) QString & replace (QLatin1String before , QLatin1String after , Qt::CaseSensitivity cs = Qt::CaseSensitive) QString & replace (QLatin1String before , const QString & after , Qt::CaseSensitivity cs = Qt::CaseSensitive) QString & replace (const QString & before , QLatin1String after , Qt::CaseSensitivity cs = Qt::CaseSensitive) QString & replace (const QString & before , const QString & after , Qt::CaseSensitivity cs = Qt::CaseSensitive) QString & replace (QChar ch , const QString & after , Qt::CaseSensitivity cs = Qt::CaseSensitive) QString & replace (QChar c , QLatin1String after , Qt::CaseSensitivity cs = Qt::CaseSensitive) QString & replace (const QRegExp & rx , const QString & after ) QString & replace (const QRegularExpression & re , const QString & after ) void reserve (int size ) void resize (int size ) void resize (int size , QChar fillChar ) QString right (int n ) const QString rightJustified (int width , QChar fill = QLatin1Char( ' ' ), bool truncate = false) const QStringRef rightRef (int n ) const QString section (QChar sep , int start , int end = -1, SectionFlags flags = SectionDefault) const QString section (const QString & sep , int start , int end = -1, SectionFlags flags = SectionDefault) const QString section (const QRegExp & reg , int start , int end = -1, SectionFlags flags = SectionDefault) const QString section (const QRegularExpression & re , int start , int end = -1, SectionFlags flags = SectionDefault) const QString & setNum (int n , int base = 10) QString & setNum (ushort n , int base = 10) QString & setNum (short n , int base = 10) QString & setNum (uint n , int base = 10) QString & setNum (long n , int base = 10) QString & setNum (ulong n , int base = 10) QString & setNum (qlonglong n , int base = 10) QString & setNum (qulonglong n , int base = 10) QString & setNum (float n , char format = 'g', int precision = 6) QString & setNum (double n , char format = 'g', int precision = 6) QString & setRawData (const QChar * unicode , int size ) QString & setUnicode (const QChar * unicode , int size ) QString & setUtf16 (const ushort * unicode , int size ) QString simplified () const int size () const QStringList split (const QString & sep , SplitBehavior behavior = KeepEmptyParts, Qt::CaseSensitivity cs = Qt::CaseSensitive) const QStringList split (QChar sep , SplitBehavior behavior = KeepEmptyParts, Qt::CaseSensitivity cs = Qt::CaseSensitive) const QStringList split (const QRegExp & rx , SplitBehavior behavior = KeepEmptyParts) const QStringList split (const QRegularExpression & re , SplitBehavior behavior = KeepEmptyParts) const QVector splitRef (const QString & sep , SplitBehavior behavior = KeepEmptyParts, Qt::CaseSensitivity cs = Qt::CaseSensitive) const QVector splitRef (QChar sep , SplitBehavior behavior = KeepEmptyParts, Qt::CaseSensitivity cs = Qt::CaseSensitive) const QVector splitRef (const QRegExp & rx , SplitBehavior behavior = KeepEmptyParts) const QVector splitRef (const QRegularExpression & re , SplitBehavior behavior = KeepEmptyParts) const void squeeze () bool startsWith (const QString & s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const bool startsWith (const QStringRef & s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const bool startsWith (QLatin1String s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const bool startsWith (QChar c , Qt::CaseSensitivity cs = Qt::CaseSensitive) const void swap (QString & other ) CFStringRef toCFString () const QString toCaseFolded () const double toDouble (bool * ok = Q_NULLPTR) const float toFloat (bool * ok = Q_NULLPTR) const QString toHtmlEscaped () const int toInt (bool * ok = Q_NULLPTR, int base = 10) const QByteArray toLatin1 () const QByteArray toLocal8Bit () const long toLong (bool * ok = Q_NULLPTR, int base = 10) const qlonglong toLongLong (bool * ok = Q_NULLPTR, int base = 10) const QString toLower () const NSString * toNSString () const short toShort (bool * ok = Q_NULLPTR, int base = 10) const std::string toStdString () const std::u16string toStdU16String () const std::u32string toStdU32String () const std::wstring toStdWString () const uint toUInt (bool * ok = Q_NULLPTR, int base = 10) const ulong toULong (bool * ok = Q_NULLPTR, int base = 10) const qulonglong toULongLong (bool * ok = Q_NULLPTR, int base = 10) const ushort toUShort (bool * ok = Q_NULLPTR, int base = 10) const QVector toUcs4 () const QString toUpper () const QByteArray toUtf8 () const int toWCharArray (wchar_t * array ) const QString trimmed () const void truncate (int position ) const QChar * unicode () const const ushort * utf16 () const bool operator!= (QLatin1String other ) const bool operator!= (const char * other ) const bool operator!= (const QByteArray & other ) const QString & operator+= (const QString & other ) QString & operator+= (QChar ch ) QString & operator+= (const QStringRef & str ) QString & operator+= (QLatin1String str ) QString & operator+= (const char * str ) QString & operator+= (const QByteArray & ba ) QString & operator+= (char ch ) bool operator< (QLatin1String other ) const bool operator< (const char * other ) const bool operator< (const QByteArray & other ) const bool operator<= (QLatin1String other ) const bool operator<= (const char * other ) const bool operator<= (const QByteArray & other ) const QString & operator= (const QString & other ) QString & operator= (QChar ch ) QString & operator= (QLatin1String str ) QString & operator= (QString && other ) QString & operator= (const char * str ) QString & operator= (const QByteArray & ba ) QString & operator= (char ch ) QString & operator= ( const Null & ) bool operator== (QLatin1String other ) const bool operator== (const char * other ) const bool operator== (const QByteArray & other ) const bool operator> (QLatin1String other ) const bool operator> (const char * other ) const bool operator> (const QByteArray & other ) const bool operator>= (QLatin1String other ) const bool operator>= (const char * other ) const bool operator>= (const QByteArray & other ) const QCharRef operator[] (int position ) const QChar operator[] (int position ) const const QChar operator[] (uint position ) const QCharRef operator[] (uint position )

静态公共成员

 QString asprintf (const char * cformat , ... ) int compare (const QString & s1 , const QString & s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive) int compare (const QString & s1 , QLatin1String s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive) int compare (QLatin1String s1 , const QString & s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive) int compare (const QString & s1 , const QStringRef & s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive) QString fromCFString (CFStringRef string ) QString fromLatin1 (const char * str , int size = -1) QString fromLatin1 (const QByteArray & str ) QString fromLocal8Bit (const char * str , int size = -1) QString fromLocal8Bit (const QByteArray & str ) QString fromNSString (const NSString * string ) QString fromRawData (const QChar * unicode , int size ) QString fromStdString (const std::string & str ) QString fromStdU16String (const std::u16string & str ) QString fromStdU32String (const std::u32string & str ) QString fromStdWString (const std::wstring & str ) QString fromUcs4 (const uint * unicode , int size = -1) QString fromUcs4 (const char32_t * str , int size = -1) QString fromUtf8 (const char * str , int size = -1) QString fromUtf8 (const QByteArray & str ) QString fromUtf16 (const ushort * unicode , int size = -1) QString fromUtf16 (const char16_t * str , int size = -1) QString fromWCharArray (const wchar_t * string , int size = -1) int localeAwareCompare (const QString & s1 , const QString & s2 ) int localeAwareCompare (const QString & s1 , const QStringRef & s2 ) QString number (long n , int base = 10) QString number (uint n , int base = 10) QString number (int n , int base = 10) QString number (ulong n , int base = 10) QString number (qlonglong n , int base = 10) QString number (qulonglong n , int base = 10) QString number (double n , char format = 'g', int precision = 6) QString vasprintf (const char * cformat , va_list ap )
 bool operator!= (const QString & s1 , const QString & s2 ) bool operator!= (const char * s1 , const QString & s2 ) const QString operator+ (const QString & s1 , const QString & s2 ) const QString operator+ (const QString & s1 , const char * s2 ) const QString operator+ (const char * s1 , const QString & s2 ) const QString operator+ (const QString & s , char ch ) const QString operator+ (char ch , const QString & s ) bool operator< (const char * s1 , const QString & s2 ) QDataStream & operator<< (QDataStream & stream , const QString & string ) bool operator<= (const QString & s1 , const QString & s2 ) bool operator<= (const char * s1 , const QString & s2 ) bool operator== (const char * s1 , const QString & s2 ) bool operator> (const QString & s1 , const QString & s2 ) bool operator> (const char * s1 , const QString & s2 ) bool operator>= (const QString & s1 , const QString & s2 ) bool operator>= (const char * s1 , const QString & s2 ) QDataStream & operator>> (QDataStream & stream , QString & string )

宏

 QStringLiteral ( str ) QT_NO_CAST_FROM_ASCII QT_NO_CAST_TO_ASCII QT_RESTRICTED_CAST_FROM_ASCII

详细描述

QString class provides a Unicode character string.

QString stores a string of 16-bit QChar s, where each QChar corresponds one Unicode 4.0 character. (Unicode characters with code values above 65535 are stored using surrogate pairs, i.e., two consecutive QChar s.)

Unicode is an international standard that supports most of the writing systems in use today. It is a superset of US-ASCII (ANSI X3.4-1986) and Latin-1 (ISO 8859-1), and all the US-ASCII/Latin-1 characters are available at the same code positions.

Behind the scenes, QString 使用 隐式共享 (copy-on-write) to reduce memory usage and to avoid the needless copying of data. This also helps reduce the inherent overhead of storing 16-bit characters instead of 8-bit characters.

In addition to QString , Qt also provides the QByteArray class to store raw bytes and traditional 8-bit '\0'-terminated strings. For most purposes, QString is the class you want to use. It is used throughout the Qt API, and the Unicode support ensures that your applications will be easy to translate if you want to expand your application's market at some point. The two main cases where QByteArray is appropriate are when you need to store raw binary data, and when memory conservation is critical (like in embedded systems).

初始化字符串

One way to initialize a QString is simply to pass a  const char *  to its constructor. For example, the following code creates a QString of size 5 containing the data "Hello":

QString str = "Hello";


QString converts the  const char *  data into Unicode using the fromUtf8 () 函数。

In all of the QString functions that take  const char *  parameters, the  const char *  is interpreted as a classic C-style '\0'-terminated string encoded in UTF-8. It is legal for the  const char *  parameter to be 0.

You can also provide string data as an array of QChar s:

static const QChar data[4] = { 0x0055, 0x006e, 0x10e3, 0x03a3 };
QString str(data, 4);


QString makes a deep copy of the QChar data, so you can modify it later without experiencing side effects. (If for performance reasons you don't want to take a deep copy of the character data, use QString::fromRawData () instead.)

Another approach is to set the size of the string using resize () and to initialize the data character per character. QString uses 0-based indexes, just like C++ arrays. To access the character at a particular index position, you can use operator[] (). On non-const strings, operator[] () returns a reference to a character that can be used on the left side of an assignment. For example:

QString str;
str.resize(4);
str[0] = QChar('U');
str[1] = QChar('n');
str[2] = QChar(0x10e3);
str[3] = QChar(0x03a3);


For read-only access, an alternative syntax is to use the at () 函数：

QString str;
for (int i = 0; i < str.size(); ++i) {
if (str.at(i) >= QChar('a') && str.at(i) <= QChar('f'))
qDebug() << "Found character in range [a-f]";
}


at () function can be faster than operator[] (), because it never causes a deep copy to occur. Alternatively, use the left (), right ()，或 mid () functions to extract several characters at a time.

A QString can embed '\0' characters ( QChar::Null ). The size () function always returns the size of the whole string, including embedded '\0' characters.

After a call to the resize () function, newly allocated characters have undefined values. To set all the characters in the string to a particular value, use the fill () 函数。

QString provides dozens of overloads designed to simplify string usage. For example, if you want to compare a QString with a string literal, you can write code like this and it will work as expected:

QString str;
if (str == "auto" || str == "extern"
|| str == "static" || str == "register") {
// ...
}


You can also pass string literals to functions that take QStrings as arguments, invoking the QString (const char *) constructor. Similarly, you can pass a QString to a function that takes a  const char *  argument using the qPrintable () macro which returns the given QString as a  const char *  . This is equivalent to calling < QString >. toLocal8Bit (). constData ().

操纵字符串数据

QString provides the following basic functions for modifying the character data: append (), prepend (), insert (), replace ()，和 remove ()。例如：

QString str = "and";
str.prepend("rock ");     // str == "rock and"
str.append(" roll");        // str == "rock and roll"
str.replace(5, 3, "&");   // str == "rock & roll"


If you are building a QString gradually and know in advance approximately how many characters the QString will contain, you can call reserve (), asking QString to preallocate a certain amount of memory. You can also call capacity () to find out how much memory QString actually allocated.

replace () 和 remove () functions' first two arguments are the position from which to start erasing and the number of characters that should be erased. If you want to replace all occurrences of a particular substring with another, use one of the two-parameter replace () overloads.

A frequent requirement is to remove whitespace characters from a string ('\n', '\t', ' ', etc.). If you want to remove whitespace from both ends of a QString , use the trimmed () function. If you want to remove whitespace from both ends and replace multiple consecutive whitespaces with a single space character within the string, use simplified ().

If you want to find all occurrences of a particular character or substring in a QString , use the indexOf () 或 lastIndexOf () functions. The former searches forward starting from a given index position, the latter searches backward. Both return the index position of the character or substring if they find it; otherwise, they return -1. For example, here's a typical loop that finds all occurrences of a particular substring:

QString str = "We must be <b>bold</b>, very <b>bold</b>";
int j = 0;
while ((j = str.indexOf("<b>", j)) != -1) {
qDebug() << "Found <b> tag at index position" << j;
++j;
}


QString provides many functions for converting numbers into strings and strings into numbers. See the arg () functions, the setNum () functions, the number () static functions, and the toInt (), toDouble (), and similar functions.

To get an upper- or lowercase version of a string use toUpper () 或 toLower ().

Lists of strings are handled by the QStringList class. You can split a string into a list of strings using the split () function, and join a list of strings into a single string with an optional separator using QStringList::join (). You can obtain a list of strings from a string list that contain a particular substring or that match a particular QRegExp 使用 QStringList::filter () 函数。

查询字符串数据

If you want to see if a QString starts or ends with a particular substring use startsWith () 或 endsWith (). If you simply want to check whether a QString contains a particular character or substring, use the contains () function. If you want to find out how many times a particular character or substring occurs in the string, use count ().

QStrings can be compared using overloaded operators such as operator< (), operator<= (), operator== (), operator>= (), and so on. Note that the comparison is based exclusively on the numeric Unicode values of the characters. It is very fast, but is not what a human would expect; the QString::localeAwareCompare () function is a better choice for sorting user-interface strings.

To obtain a pointer to the actual character data, call data () 或 constData (). These functions return a pointer to the beginning of the QChar data. The pointer is guaranteed to remain valid until a non-const function is called on the QString .

在 8 位字符串和 Unicode 字符串之间转换

QString provides the following three functions that return a  const char *  version of the string as QByteArray : toUtf8 (), toLatin1 ()，和 toLocal8Bit ().

• toLatin1 () returns a Latin-1 (ISO 8859-1) encoded 8-bit string.
• toUtf8 () returns a UTF-8 encoded 8-bit string. UTF-8 is a superset of US-ASCII (ANSI X3.4-1986) that supports the entire Unicode character set through multibyte sequences.
• toLocal8Bit () returns an 8-bit string using the system's local encoding.

To convert from one of these encodings, QString 提供 fromLatin1 (), fromUtf8 ()，和 fromLocal8Bit (). Other encodings are supported through the QTextCodec 类。

As mentioned above, QString provides a lot of functions and operators that make it easy to interoperate with  const char *  strings. But this functionality is a double-edged sword: It makes QString more convenient to use if all strings are US-ASCII or Latin-1, but there is always the risk that an implicit conversion from or to  const char *  is done using the wrong 8-bit encoding. To minimize these risks, you can turn off these implicit conversions by defining the following two preprocessor symbols:

•  QT_NO_CAST_FROM_ASCII  disables automatic conversions from C string literals and pointers to Unicode.
•  QT_RESTRICTED_CAST_FROM_ASCII  allows automatic conversions from C characters and character arrays, but disables automatic conversions from character pointers to Unicode.
•  QT_NO_CAST_TO_ASCII  disables automatic conversion from QString to C strings.

One way to define these preprocessor symbols globally for your application is to add the following entry to your qmake project file :

DEFINES += QT_NO_CAST_FROM_ASCII \
QT_NO_CAST_TO_ASCII


You then need to explicitly call fromUtf8 (), fromLatin1 ()，或 fromLocal8Bit () to construct a QString from an 8-bit string, or use the lightweight QLatin1String class, for example:

QString url = QLatin1String("http://www.unicode.org/");


Similarly, you must call toLatin1 (), toUtf8 ()，或 toLocal8Bit () explicitly to convert the QString to an 8-bit string. (Other encodings are supported through the QTextCodec class.)

Note for C Programmers
Due to C++'s type system and the fact that QString is implicitly shared , QStrings may be treated like  int  s or other basic types. For example:
QString Widget::boolToString(bool b)
{
QString result;
if (b)
result = "True";
else
result = "False";
return result;
}


 result  variable, is a normal variable allocated on the stack. When  return  is called, and because we're returning by value, the copy constructor is called and a copy of the string is returned. No actual copying takes place thanks to the implicit sharing.

在　Null 和空字符串之间的区别

For historical reasons, QString distinguishes between a null string and an empty string. A null string is a string that is initialized using QString 's default constructor or by passing (const char *)0 to the constructor. An empty string is any string with size 0. A null string is always empty, but an empty string isn't necessarily null:

QString().isNull();               // returns true
QString().isEmpty();              // returns true
QString("").isNull();             // returns false
QString("").isEmpty();            // returns true
QString("abc").isNull();          // returns false
QString("abc").isEmpty();         // returns false


All functions except isNull () treat null strings the same as empty strings. For example, toUtf8 (). constData () returns a pointer to a '\0' character for a null string ( not a null pointer), and QString () compares equal to QString (""). We recommend that you always use the isEmpty () function and avoid isNull ().

自变量格式

In member functions where an argument format can be specified (e.g., arg (), number ()), the argument format can be one of the following:

Format 含义
 e  format as [-]9.9e[+|-]999
 E  format as [-]9.9E[+|-]999
 f  format as [-]9.9
 g  use  e  or  f  format, whichever is the most concise
 G  use  E  or  f  format, whichever is the most concise

A precision is also specified with the argument format . For the 'e', 'E', and 'f' formats, the precision represents the number of digits after the decimal point. For the 'g' and 'G' formats, the precision represents the maximum number of significant digits (trailing zeroes are omitted).

更高效的字符串构造

Many strings are known at compile time. But the trivial constructor QString ("Hello"), will copy the contents of the string, treating the contents as Latin-1. To avoid this one can use the QStringLiteral macro to directly create the required data at compile time. Constructing a QString out of the literal does then not cause any overhead at runtime.

A slightly less efficient way is to use QLatin1String . This class wraps a C string literal, precalculates it length at compile time and can then be used for faster comparison with QStrings and conversion to QStrings than a regular C string literal.

    QString foo;
QString type = "long";
foo->setText(QLatin1String("vector<") + type + QLatin1String(">::iterator"));
if (foo.startsWith("(" + type + ") 0x"))
...


There is nothing wrong with either of these string constructions, but there are a few hidden inefficiencies. Beginning with Qt 4.6, you can eliminate them.

First, multiple uses of the  '+'  operator usually means multiple memory allocations. When concatenating n substrings, where n > 2 , there can be as many as n - 1 calls to the memory allocator.

In 4.6, an internal template class  QStringBuilder  has been added along with a few helper functions. This class is marked internal and does not appear in the documentation, because you aren't meant to instantiate it in your code. Its use will be automatic, as described below. The class is found in  src/corelib/tools/qstringbuilder.cpp  if you want to have a look at it.

 QStringBuilder  uses expression templates and reimplements the  '%'  operator so that when you use  '%'  for string concatenation instead of  '+'  , multiple substring concatenations will be postponed until the final result is about to be assigned to a QString . At this point, the amount of memory required for the final result is known. The memory allocator is then called once to get the required space, and the substrings are copied into it one by one.

Additional efficiency is gained by inlining and reduced reference counting (the QString created from a  QStringBuilder  typically has a ref count of 1, whereas QString::append () needs an extra test).

There are two ways you can access this improved method of string construction. The straightforward way is to include  QStringBuilder  wherever you want to use it, and use the  '%'  operator instead of  '+'  when concatenating strings:

    #include <QStringBuilder>
QString hello("hello");
QStringRef el(&hello, 2, 3);
QLatin1String world("world");
QString message =  hello % el % world % QChar('!');


A more global approach which is the most convenient but not entirely source compatible, is to this define in your .pro file:

    DEFINES *= QT_USE_QSTRINGBUILDER


 '+'  will automatically be performed as the  QStringBuilder   '%'  everywhere.

成员类型文档编制

typedef QString:: ConstIterator

Qt 样式同义词为 QString::const_iterator .

typedef QString:: Iterator

Qt 样式同义词为 QString::iterator .

enum QString:: NormalizationForm

This enum describes the various normalized forms of Unicode text.

 QString::NormalizationForm_D   0  Canonical Decomposition
 QString::NormalizationForm_C   1  Canonical Decomposition followed by Canonical Composition
 QString::NormalizationForm_KD   2  Compatibility Decomposition
 QString::NormalizationForm_KC   3  Compatibility Decomposition followed by Canonical Composition

enum QString:: SectionFlag flags QString:: SectionFlags

This enum specifies flags that can be used to affect various aspects of the section () function's behavior with respect to separators and empty fields.

 QString::SectionDefault   0x00  Empty fields are counted, leading and trailing separators are not included, and the separator is compared case sensitively.
 QString::SectionSkipEmpty   0x01  Treat empty fields as if they don't exist, i.e. they are not considered as far as start and end are concerned.
 QString::SectionIncludeLeadingSep   0x02  Include the leading separator (if any) in the result string.
 QString::SectionIncludeTrailingSep   0x04  Include the trailing separator (if any) in the result string.
 QString::SectionCaseInsensitiveSeps   0x08  Compare the separator case-insensitively.

The SectionFlags type is a typedef for QFlags <SectionFlag>. It stores an OR combination of SectionFlag values.

enum QString:: SplitBehavior

This enum specifies how the split () function should behave with respect to empty strings.

 QString::KeepEmptyParts   0  If a field is empty, keep it in the result.
 QString::SkipEmptyParts   1  If a field is empty, don't include it in the result.

typedef QString:: const_iterator

This typedef provides an STL-style const iterator for QString .

typedef QString:: const_pointer

The QString::const_pointer typedef provides an STL-style const pointer to a QString element ( QChar ).

typedef QString:: const_reference

This typedef provides an STL-style const reference for a QString element ( QChar ).

typedef QString:: const_reverse_iterator

This typedef provides an STL-style const reverse iterator for QString .

This typedef was introduced in Qt 5.6.

typedef QString:: difference_type

QString::size_type typedef provides an STL-style type for difference between pointers.

typedef QString:: iterator

The QString::iterator typedef provides an STL-style non-const iterator for QString .

typedef QString:: pointer

QString::const_pointer typedef provides an STL-style pointer to a QString element ( QChar ).

typedef QString:: reference

This typedef provides an STL-style reference for a QString element ( QChar ).

typedef QString:: reverse_iterator

This typedef provides an STL-style non-const reverse iterator for QString .

This typedef was introduced in Qt 5.6.

typedef QString:: size_type

The QString::size_type typedef provides an STL-style type for sizes (int).

typedef QString:: value_type

This typedef provides an STL-style value type for QString .

成员函数文档编制

QString:: QString ()

Constructs a null string. Null strings are also empty.

QString:: QString (const QChar * unicode , int size = -1)

Constructs a string initialized with the first size characters of the QChar array unicode .

unicode is 0, a null string is constructed.

size is negative, unicode is assumed to point to a nul-terminated array and its length is determined dynamically. The terminating nul-character is not considered part of the string.

QString makes a deep copy of the string data. The unicode data is copied as is and the Byte Order Mark is preserved if present.

QString:: QString ( QChar ch )

Constructs a string of size 1 containing the character ch .

QString:: QString ( int size , QChar ch )

Constructs a string of the given size with every character set to ch .

QString:: QString ( QLatin1String str )

Constructs a copy of the Latin-1 string str .

QString:: QString (const QString & other )

This operation takes constant time , because QString is implicitly shared . This makes returning a QString from a function very fast. If a shared instance is modified, it will be copied (copy-on-write), and that takes linear time .

QString:: QString ( QString && other )

Move-constructs a QString instance, making it point at the same object that other 所指向的。

QString:: QString (const char * str )

Constructs a string initialized with the 8-bit string str . The given const char pointer is converted to Unicode using the fromUtf8 () 函数。

You can disable this constructor by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

QString:: QString (const QByteArray & ba )

Constructs a string initialized with the byte array ba . The given byte array is converted to Unicode using fromUtf8 (). Stops copying at the first 0 character, otherwise copies the entire byte array.

You can disable this constructor by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

QString:: ~QString ()

Destroys the string.

QString &QString:: append (const QString & str )

Appends the string str onto the end of this string.

QString x = "free";
QString y = "dom";
x.append(y);
// x == "freedom"


This is the same as using the insert () 函数：

x.insert(x.size(), y);


The append() function is typically very fast ( constant time ), because QString preallocates extra space at the end of the string data so it can grow without reallocating the entire string each time.

QString &QString:: append ( QChar ch )

Appends the character ch to this string.

QString &QString:: append (const QStringRef & reference )

Appends the given string reference to this string and returns the result.

QString &QString:: append ( QLatin1String str )

Appends the Latin-1 string str to this string.

QString &QString:: append (const char * str )

Appends the string str to this string. The given const char pointer is converted to Unicode using the fromUtf8 () 函数。

You can disable this function by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

QString &QString:: append (const QByteArray & ba )

Appends the byte array ba to this string. The given byte array is converted to Unicode using the fromUtf8 () 函数。

You can disable this function by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

QString QString:: arg (const QString & a , int fieldWidth = 0, QChar fillChar = QLatin1Char( ' ' )) const

Returns a copy of this string with the lowest numbered place marker replaced by string a , i.e.,  %1  ,  %2  , ...,  %99  .

fieldWidth specifies the minimum amount of space that argument a shall occupy. If a requires less space than fieldWidth , it is padded to fieldWidth with character fillChar . A positive fieldWidth produces right-aligned text. A negative fieldWidth produces left-aligned text.

This example shows how we might create a  status  string for reporting progress while processing a list of files:

QString i;           // current file's number
QString total;       // number of files to process
QString fileName;    // current file's name
QString status = QString("Processing file %1 of %2: %3")
.arg(i).arg(total).arg(fileName);


First,  arg(i)  replaces  %1  . Then  arg(total)  replaces  %2  . Finally,  arg(fileName)  replaces  %3  .

One advantage of using arg() over asprintf () is that the order of the numbered place markers can change, if the application's strings are translated into other languages, but each arg() will still replace the lowest numbered unreplaced place marker, no matter where it appears. Also, if place marker  %i  appears more than once in the string, the arg() replaces all of them.

If there is no unreplaced place marker remaining, a warning message is output and the result is undefined. Place marker numbers must be in the range 1 to 99.

QString QString:: arg ( qulonglong a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

base argument specifies the base to use when converting the integer a into a string. base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

QString QString:: arg ( long a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

a argument is expressed in the given base , which is 10 by default and must be between 2 and 36.

The '%' can be followed by an 'L', in which case the sequence is replaced with a localized representation of a . The conversion uses the default locale. The default locale is determined from the system's locale settings at application startup. It can be changed using QLocale::setDefault (). The 'L' flag is ignored if base is not 10.

QString str;
str = QString("Decimal 63 is %1 in hexadecimal")
.arg(63, 0, 16);
// str == "Decimal 63 is 3f in hexadecimal"
QLocale::setDefault(QLocale(QLocale::English, QLocale::UnitedStates));
str = QString("%1 %L2 %L3")
.arg(12345)
.arg(12345)
.arg(12345, 0, 16);
// str == "12345 12,345 3039"


fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

QString QString:: arg ( ulong a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

base argument specifies the base to use when converting the integer a to a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

QString QString:: arg ( int a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const

a argument is expressed in base base , which is 10 by default and must be between 2 and 36. For bases other than 10, a is treated as an unsigned integer.

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

The '%' can be followed by an 'L', in which case the sequence is replaced with a localized representation of a . The conversion uses the default locale, set by QLocale::setDefault (). If no default locale was specified, the "C" locale is used. The 'L' flag is ignored if base is not 10.

QString str;
str = QString("Decimal 63 is %1 in hexadecimal")
.arg(63, 0, 16);
// str == "Decimal 63 is 3f in hexadecimal"
QLocale::setDefault(QLocale(QLocale::English, QLocale::UnitedStates));
str = QString("%1 %L2 %L3")
.arg(12345)
.arg(12345)
.arg(12345, 0, 16);
// str == "12345 12,345 3039"


fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

QString QString:: arg ( uint a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const

base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36.

fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

QString QString:: arg ( short a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

QString QString:: arg ( ushort a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

QString QString:: arg ( double a , int fieldWidth = 0, char format = 'g', int precision = -1, QChar fillChar = QLatin1Char( ' ' )) const

Argument a is formatted according to the specified format and precision 。见 自变量格式 了解细节。

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

double d = 12.34;
QString str = QString("delta: %1").arg(d, 0, 'E', 3);
// str == "delta: 1.234E+01"


The '%' can be followed by an 'L', in which case the sequence is replaced with a localized representation of a . The conversion uses the default locale, set by QLocale::setDefault (). If no default locale was specified, the "C" locale is used.

fillChar is '0' (the number 0, ASCII 48), this function will use the locale's zero to pad. For negative numbers, the zero padding will probably appear before the minus sign.

QString QString:: arg ( char a , int fieldWidth = 0, QChar fillChar = QLatin1Char( ' ' )) const

a argument is interpreted as a Latin-1 character.

QString QString:: arg ( qlonglong a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char( ' ' )) const

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

QString QString:: arg (const QString & a1 , const QString & a2 ) const

QString str;
str = "%1 %2";
str.arg("%1f", "Hello");        // returns "%1f Hello"
str.arg("%1f").arg("Hello");    // returns "Hellof %2"


A similar problem occurs when the numbered place markers are not white space separated:

QString str;
str = "%1%3%2";
str.arg("Hello").arg(20).arg(50); // returns "Hello500"
str = "%1%2%3";
str.arg("Hello").arg(50).arg(20); // returns "Hello5020"


Let's look at the substitutions:

• First,  Hello  replaces  %1  so the string becomes  "Hello%3%2"  .
• Then,  20  replaces  %2  so the string becomes  "Hello%320"  .
• Since the maximum numbered place marker value is 99,  50  replaces  %32  .

Thus the string finally becomes  "Hello500"  .

In such cases, the following yields the expected results:

QString str;
str = "%1%2%3";
str.arg("Hello", QString::number(20), QString::number(50)); // returns "Hello5020"


 [static]  QString QString:: asprintf (const char * cformat , ... )

Safely builds a formatted string from the format string cformat and an arbitrary list of arguments.

The format string supports the conversion specifiers, length modifiers, and flags provided by printf() in the standard C++ library. The cformat string and  %s  arguments must be UTF-8 encoded.

QString result;
QTextStream(&result) << "pi = " << 3.14;
// result == "pi = 3.14"


For translations , especially if the strings contains more than one escape sequence, you should consider using the arg () function instead. This allows the order of the replacements to be controlled by the translator.

const QChar QString:: at ( int position ) const

Returns the character at the given index position in the string.

position must be a valid index position in the string (i.e., 0 <= position < size ()).

int QString:: capacity () const

Returns the maximum number of characters that can be stored in the string without forcing a reallocation.

The sole purpose of this function is to provide a means of fine tuning QString 's memory usage. In general, you will rarely ever need to call this function. If you want to know how many characters are in the string, call size ().

void QString:: chop ( int n )

n is greater than or equal to size (), the result is an empty string; if n is negative, it is equivalent to passing zero.

QString str("LOGOUT\r\n");
str.chop(2);
// str == "LOGOUT"


If you want to remove characters from the beginning of the string, use remove () 代替。

Clears the contents of the string and makes it null.

 [static]  int QString:: compare (const QString & s1 , const QString & s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Compares s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2 .

cs is Qt::CaseSensitive , the comparison is case sensitive; otherwise the comparison is case insensitive.

Case sensitive comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-visible strings with localeAwareCompare ().

int x = QString::compare("aUtO", "AuTo", Qt::CaseInsensitive);  // x == 0
int y = QString::compare("auto", "Car", Qt::CaseSensitive);     // y > 0
int z = QString::compare("auto", "Car", Qt::CaseInsensitive);   // z < 0


int QString:: compare ( QLatin1String other , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Same as compare(*this, other , cs ).

int QString:: compare (const QString & other , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Lexically compares this string with the other string and returns an integer less than, equal to, or greater than zero if this string is less than, equal to, or greater than the other string.

Same as compare(*this, other , cs ).

 [static]  int QString:: compare (const QString & s1 , QLatin1String s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Performs a comparison of s1 and s2 , using the case sensitivity setting cs .

 [static]  int QString:: compare ( QLatin1String s1 , const QString & s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Performs a comparison of s1 and s2 , using the case sensitivity setting cs .

int QString:: compare (const QStringRef & ref , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Compares the string reference, ref , with the string and returns an integer less than, equal to, or greater than zero if the string is less than, equal to, or greater than ref .

const QChar *QString:: constData () const

Returns a pointer to the data stored in the QString . The pointer can be used to access the characters that compose the string.

Note that the pointer remains valid only as long as the string is not modified.

bool QString:: contains (const QString & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString str = "Peter Pan";
str.contains("peter", Qt::CaseInsensitive);    // returns true


bool QString:: contains (const QStringRef & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

bool QString:: contains ( QRegExp & rx ) const

If there is a match, the rx regular expression will contain the matched captures (see QRegExp::matchedLength , QRegExp::cap ).

bool QString:: contains (const QRegularExpression & re , QRegularExpressionMatch * match ) const

If the match is successful and match is not a null pointer, it also writes the results of the match into the QRegularExpressionMatch object pointed to by match .

int QString:: count (const QString & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the number of (potentially overlapping) occurrences of the string str in this string.

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

int QString:: count ( QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the number of occurrences of character ch in the string.

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

int QString:: count (const QStringRef & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the number of (potentially overlapping) occurrences of the string reference str in this string.

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

int QString:: count (const QRegExp & rx ) const

Returns the number of times the regular expression rx matches in the string.

This function counts overlapping matches, so in the example below, there are four instances of "ana" or "ama":

QString str = "banana and panama";
str.count(QRegExp("a[nm]a"));    // returns 4


int QString:: count (const QRegularExpression & re ) const

Returns the number of times the regular expression re matches in the string.

This function counts overlapping matches, so in the example below, there are four instances of "ana" or "ama":

QString str = "banana and panama";
str.count(QRegularExpression("a[nm]a"));    // returns 4


QChar *QString:: data ()

Returns a pointer to the data stored in the QString . The pointer can be used to access and modify the characters that compose the string.

QString str = "Hello world";
QChar *data = str.data();
while (!data->isNull()) {
qDebug() << data->unicode();
++data;
}


Note that the pointer remains valid only as long as the string is not modified by other means. For read-only access, constData () is faster because it never causes a deep copy to occur.

bool QString:: endsWith (const QString & s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString str = "Bananas";
str.endsWith("anas");         // returns true
str.endsWith("pple");         // returns false


bool QString:: endsWith (const QStringRef & s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString &QString:: fill ( QChar ch , int size = -1)

Sets every character in the string to character ch 。若 size is different from -1 (default), the string is resized to size beforehand.

QString str = "Berlin";
str.fill('z');
// str == "zzzzzz"
str.fill('A', 2);
// str == "AA"


 [static]  QString QString:: fromLatin1 (const char * str , int size = -1)

size is -1 (default), it is taken to be strlen( str ).

 [static]  QString QString:: fromLocal8Bit (const char * str , int size = -1)

size is -1 (default), it is taken to be strlen( str ).

QTextCodec::codecForLocale () is used to perform the conversion.

 [static]  QString QString:: fromRawData (const QChar * unicode , int size )

Any attempts to modify the QString or copies of it will cause it to create a deep copy of the data, ensuring that the raw data isn't modified.

Here's an example of how we can use a QRegularExpression on raw data in memory without requiring to copy the data into a QString :

QRegularExpression pattern("\u00A4");
static const QChar unicode[] = {
0x005A, 0x007F, 0x00A4, 0x0060,
0x1009, 0x0020, 0x0020};
int size = sizeof(unicode) / sizeof(QChar);
QString str = QString::fromRawData(unicode, size);
if (str.contains(pattern) {
// ...
}


 [static]  QString QString:: fromUcs4 (const uint * unicode , int size = -1)

size is -1 (default), unicode must be terminated with a 0.

 [static]  QString QString:: fromUcs4 (const char32_t * str , int size = -1)

size is -1 (default), str must be terminated with a 0.

 [static]  QString QString:: fromUtf8 (const char * str , int size = -1)

size is -1 (default), it is taken to be strlen( str ).

UTF-8 is a Unicode codec and can represent all characters in a Unicode string like QString . However, invalid sequences are possible with UTF-8 and, if any such are found, they will be replaced with one or more "replacement characters", or suppressed. These include non-Unicode sequences, non-characters, overlong sequences or surrogate codepoints encoded into UTF-8.

This function can be used to process incoming data incrementally as long as all UTF-8 characters are terminated within the incoming data. Any unterminated characters at the end of the string will be replaced or suppressed. In order to do stateful decoding, please use QTextDecoder .

 [static]  QString QString:: fromUtf16 (const ushort * unicode , int size = -1)

size is -1 (default), unicode must be terminated with a 0.

This function checks for a Byte Order Mark (BOM). If it is missing, host byte order is assumed.

This function is slow compared to the other Unicode conversions. Use QString (const QChar *, int) or QString (const QChar *) if possible.

QString makes a deep copy of the Unicode data.

 [static]  QString QString:: fromUtf16 (const char16_t * str , int size = -1)

size is -1 (default), str must be terminated with a 0.

This function checks for a Byte Order Mark (BOM). If it is missing, host byte order is assumed.

This function is slow compared to the other Unicode conversions. Use QString (const QChar *, int) or QString (const QChar *) if possible.

QString makes a deep copy of the Unicode data.

 [static]  QString QString:: fromWCharArray (const wchar_t * string , int size = -1)

size is -1 (default), the string has to be 0 terminated.

int QString:: indexOf (const QString & str , int from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the index position of the first occurrence of the string str in this string, searching forward from index position from . Returns -1 if str 找不到。

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString x = "sticky question";
QString y = "sti";
x.indexOf(y);               // returns 0
x.indexOf(y, 1);            // returns 10
x.indexOf(y, 10);           // returns 10
x.indexOf(y, 11);           // returns -1


from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.

int QString:: indexOf ( QChar ch , int from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the index position of the first occurrence of the character ch in the string, searching forward from index position from . Returns -1 if ch could not be found.

int QString:: indexOf ( QLatin1String str , int from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the index position of the first occurrence of the string str in this string, searching forward from index position from . Returns -1 if str 找不到。

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString x = "sticky question";
QString y = "sti";
x.indexOf(y);               // returns 0
x.indexOf(y, 1);            // returns 10
x.indexOf(y, 10);           // returns 10
x.indexOf(y, 11);           // returns -1


from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.

int QString:: indexOf (const QStringRef & str , int from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the index position of the first occurrence of the string reference str in this string, searching forward from index position from . Returns -1 if str 找不到。

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

int QString:: indexOf (const QRegExp & rx , int from = 0) const

Returns the index position of the first match of the regular expression rx in the string, searching forward from index position from . Returns -1 if rx didn't match anywhere.

QString str = "the minimum";
str.indexOf(QRegExp("m[aeiou]"), 0);       // returns 4


int QString:: indexOf ( QRegExp & rx , int from = 0) const

Returns the index position of the first match of the regular expression rx in the string, searching forward from index position from . Returns -1 if rx didn't match anywhere.

If there is a match, the rx regular expression will contain the matched captures (see QRegExp::matchedLength , QRegExp::cap ).

QString str = "the minimum";
str.indexOf(QRegExp("m[aeiou]"), 0);       // returns 4


int QString:: indexOf (const QRegularExpression & re , int from = 0) const

Returns the index position of the first match of the regular expression re in the string, searching forward from index position from . Returns -1 if re didn't match anywhere.

QString str = "the minimum";
str.indexOf(QRegularExpression("m[aeiou]"), 0);       // returns 4


int QString:: indexOf (const QRegularExpression & re , int from , QRegularExpressionMatch * rmatch ) const

Returns the index position of the first match of the regular expression re in the string, searching forward from index position from . Returns -1 if re didn't match anywhere.

If the match is successful and rmatch is not a null pointer, it also writes the results of the match into the QRegularExpressionMatch object pointed to by rmatch .

QString str = "the minimum";
QRegularExpressionMatch match;
str.indexOf(QRegularExpression("m[aeiou]"), 0, &match);       // returns 4
// match.captured() == mi


QString &QString:: insert ( int position , const QString & str )

Inserts the string str at the given index position and returns a reference to this string.

QString str = "Meal";
str.insert(1, QString("ontr"));
// str == "Montreal"


QString &QString:: insert ( int position , const QChar * unicode , int size )

Inserts the first size characters of the QChar array unicode at the given index position in the string.

QString &QString:: insert ( int position , const QStringRef & str )

Inserts the string reference str at the given index position and returns a reference to this string.

QString &QString:: insert ( int position , QLatin1String str )

Inserts the Latin-1 string str at the given index position .

QString &QString:: insert ( int position , const char * str )

Inserts the C string str at the given index position and returns a reference to this string.

This function is not available when QT_NO_CAST_FROM_ASCII is defined.

QString &QString:: insert ( int position , const QByteArray & str )

Inserts the byte array str at the given index position and returns a reference to this string.

This function is not available when QT_NO_CAST_FROM_ASCII is defined.

bool QString:: isEmpty () const

QString().isEmpty();            // returns true
QString("").isEmpty();          // returns true
QString("x").isEmpty();         // returns false
QString("abc").isEmpty();       // returns false


bool QString:: isNull () const

QString().isNull();             // returns true
QString("").isNull();           // returns false
QString("abc").isNull();        // returns false


Qt makes a distinction between null strings and empty strings for historical reasons. For most applications, what matters is whether or not a string contains any data, and this can be determined using the isEmpty () 函数。

int QString:: lastIndexOf (const QString & str , int from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the index position of the last occurrence of the string str in this string, searching backward from index position from 。若 from is -1 (default), the search starts at the last character; if from is -2, at the next to last character and so on. Returns -1 if str 找不到。

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString x = "crazy azimuths";
QString y = "az";
x.lastIndexOf(y);           // returns 6
x.lastIndexOf(y, 6);        // returns 6
x.lastIndexOf(y, 5);        // returns 2
x.lastIndexOf(y, 1);        // returns -1


int QString:: lastIndexOf ( QChar ch , int from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the index position of the last occurrence of the character ch , searching backward from position from .

int QString:: lastIndexOf ( QLatin1String str , int from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the index position of the last occurrence of the string str in this string, searching backward from index position from 。若 from is -1 (default), the search starts at the last character; if from is -2, at the next to last character and so on. Returns -1 if str 找不到。

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString x = "crazy azimuths";
QString y = "az";
x.lastIndexOf(y);           // returns 6
x.lastIndexOf(y, 6);        // returns 6
x.lastIndexOf(y, 5);        // returns 2
x.lastIndexOf(y, 1);        // returns -1


int QString:: lastIndexOf (const QStringRef & str , int from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the index position of the last occurrence of the string reference str in this string, searching backward from index position from 。若 from is -1 (default), the search starts at the last character; if from is -2, at the next to last character and so on. Returns -1 if str 找不到。

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

int QString:: lastIndexOf (const QRegExp & rx , int from = -1) const

Returns the index position of the last match of the regular expression rx in the string, searching backward from index position from . Returns -1 if rx didn't match anywhere.

QString str = "the minimum";
str.lastIndexOf(QRegExp("m[aeiou]"));      // returns 8


int QString:: lastIndexOf ( QRegExp & rx , int from = -1) const

Returns the index position of the last match of the regular expression rx in the string, searching backward from index position from . Returns -1 if rx didn't match anywhere.

If there is a match, the rx regular expression will contain the matched captures (see QRegExp::matchedLength , QRegExp::cap ).

QString str = "the minimum";
str.lastIndexOf(QRegExp("m[aeiou]"));      // returns 8


int QString:: lastIndexOf (const QRegularExpression & re , int from = -1) const

Returns the index position of the last match of the regular expression re in the string, which starts before the index position from . Returns -1 if re didn't match anywhere.

QString str = "the minimum";
str.lastIndexOf(QRegularExpression("m[aeiou]"));      // returns 8


int QString:: lastIndexOf (const QRegularExpression & re , int from , QRegularExpressionMatch * rmatch ) const

Returns the index position of the last match of the regular expression re in the string, which starts before the index position from . Returns -1 if re didn't match anywhere.

If the match is successful and rmatch is not a null pointer, it also writes the results of the match into the QRegularExpressionMatch object pointed to by rmatch .

QString str = "the minimum";
QRegularExpressionMatch match;
str.lastIndexOf(QRegularExpression("m[aeiou]"), -1, &match);      // returns 8
// match.captured() == mu


QString QString:: left ( int n ) const

Returns a substring that contains the n leftmost characters of the string.

The entire string is returned if n is greater than or equal to size (), or less than zero.

QString x = "Pineapple";
QString y = x.left(4);      // y == "Pine"


QString QString:: leftJustified ( int width , QChar fill = QLatin1Char( ' ' ), bool truncate = false) const

Returns a string of size width that contains this string padded by the fill character.

truncate is  false  size () of the string is more than width , then the returned string is a copy of the string.

QString s = "apple";
QString t = s.leftJustified(8, '.');    // t == "apple..."


truncate is  true  size () of the string is more than width , then any characters in a copy of the string after position width are removed, and the copy is returned.

QString str = "Pineapple";
str = str.leftJustified(5, '.', true);    // str == "Pinea"


QStringRef QString:: leftRef ( int n ) const

Returns a substring reference to the n leftmost characters of the string.

n is greater than or equal to size (), or less than zero, a reference to the entire string is returned.

QString x = "Pineapple";
QStringRef y = x.leftRef(4);        // y == "Pine"


int QString:: length () const

Returns the number of characters in this string. Equivalent to size ().

 [static]  int QString:: localeAwareCompare (const QString & s1 , const QString & s2 )

Compares s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2 .

The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.

On macOS and iOS this function compares according the "Order for sorted lists" setting in the International preferences panel.

int QString:: localeAwareCompare (const QString & other ) const

Compares this string with the other string and returns an integer less than, equal to, or greater than zero if this string is less than, equal to, or greater than the other string.

The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.

int QString:: localeAwareCompare (const QStringRef & other ) const

Compares this string with the other string and returns an integer less than, equal to, or greater than zero if this string is less than, equal to, or greater than the other string.

The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.

 [static]  int QString:: localeAwareCompare (const QString & s1 , const QStringRef & s2 )

Compares s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2 .

The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.

QString QString:: mid ( int position , int n = -1) const

Returns a string that contains n characters of this string, starting at the specified position index.

Returns a null string if the position index exceeds the length of the string. If there are less than n characters available in the string starting at the given position ，或者若 n is -1 (default), the function returns all characters that are available from the specified position .

QString x = "Nine pineapples";
QString y = x.mid(5, 4);            // y == "pine"
QString z = x.mid(5);               // z == "pineapples"


QStringRef QString:: midRef ( int position , int n = -1) const

Returns a substring reference to n characters of this string, starting at the specified position .

position exceeds the length of the string, a null reference is returned.

If there are less than n characters available in the string, starting at the given position ，或者若 n is -1 (default), the function returns all characters from the specified position onwards.

QString x = "Nine pineapples";
QStringRef y = x.midRef(5, 4);      // y == "pine"
QStringRef z = x.midRef(5);         // z == "pineapples"


QString QString:: normalized ( NormalizationForm mode , QChar::UnicodeVersion version = QChar::Unicode_Unassigned) const

Returns the string in the given Unicode normalization mode , according to the given version of the Unicode standard.

 [static]  QString QString:: number ( long n , int base = 10)

Returns a string equivalent of the number n according to the specified base .

The base is 10 by default and must be between 2 and 36. For bases other than 10, n is treated as an unsigned integer.

The formatting always uses QLocale::C , i.e., English/UnitedStates. To get a localized string representation of a number, use QLocale::toString () with the appropriate locale.

long a = 63;
QString s = QString::number(a, 16);             // s == "3f"
QString t = QString::number(a, 16).toUpper();     // t == "3F"


 [static]  QString QString:: number ( double n , char format = 'g', int precision = 6)

Returns a string equivalent of the number n , formatted according to the specified format and precision 。见 自变量格式 了解细节。

QString &QString:: prepend (const QString & str )

QString x = "ship";
QString y = "air";
x.prepend(y);
// x == "airship"


QString &QString:: prepend (const QStringRef & str )

Prepends the string reference str to the beginning of this string and returns a reference to this string.

QString &QString:: prepend ( QLatin1String str )

Prepends the Latin-1 string str to this string.

QString &QString:: prepend (const char * str )

You can disable this function by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

QString &QString:: prepend (const QByteArray & ba )

You can disable this function by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

void QString:: push_back (const QString & other )

This function is provided for STL compatibility, appending the given other string onto the end of this string. It is equivalent to  append(other)  .

void QString:: push_back ( QChar ch )

Appends the given ch character onto the end of this string.

void QString:: push_front (const QString & other )

This function is provided for STL compatibility, prepending the given other string to the beginning of this string. It is equivalent to  prepend(other)  .

void QString:: push_front ( QChar ch )

Prepends the given ch character to the beginning of this string.

QString &QString:: remove ( int position , int n )

If the specified position index is within the string, but position + n is beyond the end of the string, the string is truncated at the specified position .

QString s = "Montreal";
s.remove(1, 4);
// s == "Meal"


QString &QString:: remove ( QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Removes every occurrence of the character ch in this string, and returns a reference to this string.

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString t = "Ali Baba";
t.remove(QChar('a'), Qt::CaseInsensitive);
// t == "li Bb"


QString &QString:: remove (const QString & str , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Removes every occurrence of the given str string in this string, and returns a reference to this string.

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString &QString:: remove (const QRegExp & rx )

Removes every occurrence of the regular expression rx in the string, and returns a reference to the string. For example:

QString r = "Telephone";
r.remove(QRegExp("[aeiou]."));
// r == "The"


QString &QString:: remove (const QRegularExpression & re )

Removes every occurrence of the regular expression re in the string, and returns a reference to the string. For example:

QString r = "Telephone";
r.remove(QRegularExpression("[aeiou]."));
// r == "The"


QString QString:: repeated ( int times ) const

Returns a copy of this string repeated the specified number of times .

times is less than 1, an empty string is returned.

QString str("ab");
str.repeated(4);            // returns "abababab"


QString &QString:: replace ( int position , int n , const QString & after )

QString x = "Say yes!";
QString y = "no";
x.replace(4, 3, y);
// x == "Say no!"


QString &QString:: replace ( QChar before , QChar after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Replaces every occurrence of the character before with the character after and returns a reference to this string.

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString &QString:: replace (const QChar * before , int blen , const QChar * after , int alen , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Replaces each occurrence in this string of the first blen characters of before with the first alen characters of after and returns a reference to this string.

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString &QString:: replace ( QLatin1String before , QLatin1String after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Replaces every occurrence of the string before with the string after and returns a reference to this string.

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString &QString:: replace ( QLatin1String before , const QString & after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Replaces every occurrence of the string before with the string after and returns a reference to this string.

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString &QString:: replace (const QString & before , QLatin1String after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Replaces every occurrence of the string before with the string after and returns a reference to this string.

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString &QString:: replace (const QString & before , const QString & after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Replaces every occurrence of the string before with the string after and returns a reference to this string.

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString str = "colour behaviour flavour neighbour";
str.replace(QString("ou"), QString("o"));
// str == "color behavior flavor neighbor"


QString equis = "xxxxxx";
equis.replace("xx", "x");
// equis == "xxx"


QString &QString:: replace ( QChar ch , const QString & after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Replaces every occurrence of the character ch in the string with after and returns a reference to this string.

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString &QString:: replace ( QChar c , QLatin1String after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Replaces every occurrence of the character c with the string after and returns a reference to this string.

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString &QString:: replace (const QRegExp & rx , const QString & after )

Replaces every occurrence of the regular expression rx in the string with after . Returns a reference to the string. For example:

QString s = "Banana";
s.replace(QRegExp("a[mn]"), "ox");
// s == "Boxoxa"


For regular expressions containing capturing parentheses , occurrences of \1 , \2 , ..., in after are replaced with rx .cap(1), cap(2), ...

QString t = "A <i>bon mot</i>.";
t.replace(QRegExp("<i>([^<]*)</i>"), "\\emph{\\1}");
// t == "A \\emph{bon mot}."


QString &QString:: replace (const QRegularExpression & re , const QString & after )

Replaces every occurrence of the regular expression re in the string with after . Returns a reference to the string. For example:

QString s = "Banana";
s.replace(QRegularExpression("a[mn]"), "ox");
// s == "Boxoxa"


For regular expressions containing capturing groups, occurrences of \1 , \2 , ..., in after are replaced with the string captured by the corresponding capturing group.

QString t = "A <i>bon mot</i>.";
t.replace(QRegularExpression("<i>([^<]*)</i>"), "\\emph{\\1}");
// t == "A \\emph{bon mot}."


void QString:: reserve ( int size )

Attempts to allocate memory for at least size characters. If you know in advance how large the string will be, you can call this function, and if you resize the string often you are likely to get better performance. If size is an underestimate, the worst that will happen is that the QString will be a bit slower.

The sole purpose of this function is to provide a means of fine tuning QString 's memory usage. In general, you will rarely ever need to call this function. If you want to change the size of the string, call resize ().

This function is useful for code that needs to build up a long string and wants to avoid repeated reallocation. In this example, we want to add to the string until some condition is  true  , and we're fairly sure that size is large enough to make a call to reserve() worthwhile:

QString result;
int maxSize;
bool condition;
QChar nextChar;
result.reserve(maxSize);
while (condition)
result.append(nextChar);
result.squeeze();


void QString:: resize ( int size )

Sets the size of the string to size characters.

size is greater than the current size, the string is extended to make it size characters long with the extra characters added to the end. The new characters are uninitialized.

size is less than the current size, characters are removed from the end.

QString s = "Hello world";
s.resize(5);
// s == "Hello"
s.resize(8);
// s == "Hello???" (where ? stands for any character)


If you want to append a certain number of identical characters to the string, use the resize (int, QChar ) overload.

If you want to expand the string so that it reaches a certain width and fill the new positions with a particular character, use the leftJustified () 函数：

size is negative, it is equivalent to passing zero.

QString r = "Hello";
r = r.leftJustified(10, ' ');
// r == "Hello     "


void QString:: resize ( int size , QChar fillChar )

QString t = "Hello";
r.resize(t.size() + 10, 'X');
// t == "HelloXXXXXXXXXX"


Returns a substring that contains the n rightmost characters of the string.

The entire string is returned if n is greater than or equal to size (), or less than zero.

QString x = "Pineapple";
QString y = x.right(5);      // y == "apple"


QString QString:: rightJustified ( int width , QChar fill = QLatin1Char( ' ' ), bool truncate = false) const

Returns a string of size () width that contains the fill character followed by the string. For example:

QString s = "apple";
QString t = s.rightJustified(8, '.');    // t == "...apple"


truncate is  false  size () of the string is more than width , then the returned string is a copy of the string.

truncate is true and the size () of the string is more than width , then the resulting string is truncated at position width .

QString str = "Pineapple";
str = str.rightJustified(5, '.', true);    // str == "Pinea"


QStringRef QString:: rightRef ( int n ) const

Returns a substring reference to the n rightmost characters of the string.

n is greater than or equal to size (), or less than zero, a reference to the entire string is returned.

QString x = "Pineapple";
QStringRef y = x.rightRef(5);       // y == "apple"


QString QString:: section ( QChar sep , int start , int end = -1, SectionFlags flags = SectionDefault) const

This function returns a section of the string.

This string is treated as a sequence of fields separated by the character, sep . The returned string consists of the fields from position start to position end inclusive. If end is not specified, all fields from position start to the end of the string are included. Fields are numbered 0, 1, 2, etc., counting from the left, and -1, -2, etc., counting from right to left.

flags argument can be used to affect some aspects of the function's behavior, e.g. whether to be case sensitive, whether to skip empty fields and how to deal with leading and trailing separators; see SectionFlags .

QString str;
QString csv = "forename,middlename,surname,phone";
QString path = "/usr/local/bin/myapp"; // First field is empty
QString::SectionFlag flag = QString::SectionSkipEmpty;
str = csv.section(',', 2, 2);   // str == "surname"
str = path.section('/', 3, 4);  // str == "bin/myapp"
str = path.section('/', 3, 3, flag); // str == "myapp"


start or end is negative, we count fields from the right of the string, the right-most field being -1, the one from right-most field being -2, and so on.

str = csv.section(',', -3, -2);  // str == "middlename,surname"
str = path.section('/', -1); // str == "myapp"


QString QString:: section (const QString & sep , int start , int end = -1, SectionFlags flags = SectionDefault) const

QString str;
QString data = "forename**middlename**surname**phone";
str = data.section("**", 2, 2); // str == "surname"
str = data.section("**", -3, -2); // str == "middlename**surname"


QString QString:: section (const QRegExp & reg , int start , int end = -1, SectionFlags flags = SectionDefault) const

This string is treated as a sequence of fields separated by the regular expression, reg .

QString line = "forename\tmiddlename  surname \t \t phone";
QRegExp sep("\\s+");
str = line.section(sep, 2, 2); // str == "surname"
str = line.section(sep, -3, -2); // str == "middlename  surname"


QString QString:: section (const QRegularExpression & re , int start , int end = -1, SectionFlags flags = SectionDefault) const

This string is treated as a sequence of fields separated by the regular expression, re .

QString line = "forename\tmiddlename  surname \t \t phone";
QRegularExpression sep("\\s+");
str = line.section(sep, 2, 2); // str == "surname"
str = line.section(sep, -3, -2); // str == "middlename  surname"


QString &QString:: setNum ( int n , int base = 10)

Sets the string to the printed value of n 以指定 base , and returns a reference to the string.

The base is 10 by default and must be between 2 and 36. For bases other than 10, n is treated as an unsigned integer.

QString str;
str.setNum(1234);       // str == "1234"


The formatting always uses QLocale::C , i.e., English/UnitedStates. To get a localized string representation of a number, use QLocale::toString () with the appropriate locale.

QString &QString:: setNum ( float n , char format = 'g', int precision = 6)

Sets the string to the printed value of n , formatted according to the given format and precision , and returns a reference to the string.

The formatting always uses QLocale::C , i.e., English/UnitedStates. To get a localized string representation of a number, use QLocale::toString () with the appropriate locale.

QString &QString:: setNum ( double n , char format = 'g', int precision = 6)

Sets the string to the printed value of n , formatted according to the given format and precision , and returns a reference to the string.

format can be 'e', 'E', 'f', 'g' or 'G' (see 自变量格式 for an explanation of the formats).

The formatting always uses QLocale::C , i.e., English/UnitedStates. To get a localized string representation of a number, use QLocale::toString () with the appropriate locale.

QString &QString:: setRawData (const QChar * unicode , int size )

Resets the QString to use the first size Unicode characters in the array unicode . The data in unicode is not copied. The caller must be able to guarantee that unicode will not be deleted or modified as long as the QString (or an unmodified copy of it) exists.

This function can be used instead of fromRawData () to re-use existings QString objects to save memory re-allocations.

QString &QString:: setUnicode (const QChar * unicode , int size )

Resizes the string to size characters and copies unicode into the string.

unicode is 0, nothing is copied, but the string is still resized to size .

QString &QString:: setUtf16 (const ushort * unicode , int size )

Resizes the string to size characters and copies unicode into the string.

unicode is 0, nothing is copied, but the string is still resized to size .

Note that unlike fromUtf16 (), this function does not consider BOMs and possibly differing byte ordering.

QString QString:: simplified () const

Returns a string that has whitespace removed from the start and the end, and that has each sequence of internal whitespace replaced with a single space.

Whitespace means any character for which QChar::isSpace () 返回  true  . This includes the ASCII characters '\t', '\n', '\v', '\f', '\r', and ' '.

QString str = "  lots\t of\nwhitespace\r\n ";
str = str.simplified();
// str == "lots of whitespace";


int QString:: size () const

Returns the number of characters in this string.

The last character in the string is at position size() - 1.

QString str = "World";
int n = str.size();         // n == 5
str.data()[0];              // returns 'W'
str.data()[4];              // returns 'd'


QStringList QString:: split (const QString & sep , SplitBehavior behavior = KeepEmptyParts, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Splits the string into substrings wherever sep occurs, and returns the list of those strings. If sep does not match anywhere in the string, split() returns a single-element list containing this string.

cs specifies whether sep should be matched case sensitively or case insensitively.

behavior is QString::SkipEmptyParts , empty entries don't appear in the result. By default, empty entries are kept.

QString str = "a,,b,c";
QStringList list1 = str.split(',');
// list1: [ "a", "", "b", "c" ]
QStringList list2 = str.split(',', QString::SkipEmptyParts);
// list2: [ "a", "b", "c" ]


sep is empty, split() returns an empty string, followed by each of the string's characters, followed by another empty string:

QString str = "abc";
auto parts = str.split("");
// parts: {"", "a", "b", "c", ""}


To understand this behavior, recall that the empty string matches everywhere, so the above is qualitatively the same as:

QString str = "/a/b/c/";
auto parts = str.split('/');
// parts: {"", "a", "b", "c", ""}


QStringList QString:: split (const QRegExp & rx , SplitBehavior behavior = KeepEmptyParts) const

Splits the string into substrings wherever the regular expression rx matches, and returns the list of those strings. If rx does not match anywhere in the string, split () returns a single-element list containing this string.

Here's an example where we extract the words in a sentence using one or more whitespace characters as the separator:

QString str;
QStringList list;
str = "Some  text\n\twith  strange whitespace.";
list = str.split(QRegExp("\\s+"));
// list: [ "Some", "text", "with", "strange", "whitespace." ]


Here's a similar example, but this time we use any sequence of non-word characters as the separator:

str = "This time, a normal English sentence.";
list = str.split(QRegExp("\\W+"), QString::SkipEmptyParts);
// list: [ "This", "time", "a", "normal", "English", "sentence" ]


Here's a third example where we use a zero-length assertion, \b (word boundary), to split the string into an alternating sequence of non-word and word tokens:

str = "Now: this sentence fragment.";
list = str.split(QRegExp("\\b"));
// list: [ "", "Now", ": ", "this", " ", "sentence", " ", "fragment", "." ]


QStringList QString:: split (const QRegularExpression & re , SplitBehavior behavior = KeepEmptyParts) const

Splits the string into substrings wherever the regular expression re matches, and returns the list of those strings. If re does not match anywhere in the string, split () returns a single-element list containing this string.

Here's an example where we extract the words in a sentence using one or more whitespace characters as the separator:

QString str;
QStringList list;
str = "Some  text\n\twith  strange whitespace.";
list = str.split(QRegularExpression("\\s+"));
// list: [ "Some", "text", "with", "strange", "whitespace." ]


Here's a similar example, but this time we use any sequence of non-word characters as the separator:

str = "This time, a normal English sentence.";
list = str.split(QRegularExpression("\\W+"), QString::SkipEmptyParts);
// list: [ "This", "time", "a", "normal", "English", "sentence" ]


Here's a third example where we use a zero-length assertion, \b (word boundary), to split the string into an alternating sequence of non-word and word tokens:

str = "Now: this sentence fragment.";
list = str.split(QRegularExpression("\\b"));
// list: [ "", "Now", ": ", "this", " ", "sentence", " ", "fragment", "." ]


QVector < QStringRef > QString:: splitRef (const QString & sep , SplitBehavior behavior = KeepEmptyParts, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Splits the string into substring references wherever sep occurs, and returns the list of those strings.

QString::split () for how sep , behavior and cs interact to form the result.

QVector < QStringRef > QString:: splitRef (const QRegExp & rx , SplitBehavior behavior = KeepEmptyParts) const

Splits the string into substring references wherever the regular expression rx matches, and returns the list of those strings. If rx does not match anywhere in the string, splitRef () returns a single-element vector containing this string reference.

QVector < QStringRef > QString:: splitRef (const QRegularExpression & re , SplitBehavior behavior = KeepEmptyParts) const

Splits the string into substring references wherever the regular expression re matches, and returns the list of those strings. If re does not match anywhere in the string, splitRef () returns a single-element vector containing this string reference.

void QString:: squeeze ()

Releases any memory not required to store the character data.

The sole purpose of this function is to provide a means of fine tuning QString 's memory usage. In general, you will rarely ever need to call this function.

bool QString:: startsWith (const QString & s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString str = "Bananas";
str.startsWith("Ban");     // returns true
str.startsWith("Car");     // returns false


bool QString:: startsWith (const QStringRef & s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

void QString:: swap ( QString & other )

Swaps string other with this string. This operation is very fast and never fails.

CFStringRef QString:: toCFString () const

Creates a CFString from a QString . The caller owns the CFString and is responsible for releasing it.

QString QString:: toCaseFolded () const

Returns the case folded equivalent of the string. For most Unicode characters this is the same as toLower ().

double QString:: toDouble ( bool * ok = Q_NULLPTR) const

Returns the string converted to a  double  值。

Returns 0.0 if the conversion fails.

If a conversion error occurs,  *  ok is set to  false  ; otherwise  *  ok is set to  true  .

QString str = "1234.56";
double val = str.toDouble();   // val == 1234.56


bool ok;
double d;
d = QString( "1234.56e-02" ).toDouble(&ok); // ok == true, d == 12.3456


The string conversion will always happen in the 'C' locale. For locale dependent conversion use QLocale::toDouble ()

d = QString( "1234,56" ).toDouble(&ok); // ok == false
d = QString( "1234.56" ).toDouble(&ok); // ok == true, d == 1234.56


For historical reasons, this function does not handle thousands group separators. If you need to convert such numbers, use QLocale::toDouble ().

d = QString( "1,234,567.89" ).toDouble(&ok); // ok == false
d = QString( "1234567.89" ).toDouble(&ok); // ok == true


float QString:: toFloat ( bool * ok = Q_NULLPTR) const

Returns the string converted to a  float  值。

If a conversion error occurs, * ok is set to  false  ; otherwise * ok is set to  true  . Returns 0.0 if the conversion fails.

The string conversion will always happen in the 'C' locale. For locale dependent conversion use QLocale::toFloat ()

QString str1 = "1234.56";
str1.toFloat();             // returns 1234.56
bool ok;
QString str2 = "R2D2";
str2.toFloat(&ok);          // returns 0.0, sets ok to false


QString QString:: toHtmlEscaped () const

Converts a plain text string to an HTML string with HTML metacharacters  <  ,  >  ,  &  ，和  "  replaced by HTML entities.

QString plain = "#include <QtCore>"
QString html = plain.toHtmlEscaped();
// html == "#include <QtCore>"


int QString:: toInt ( bool * ok = Q_NULLPTR, int base = 10) const

Returns the string converted to an  int  using base base , which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.

If a conversion error occurs, * ok is set to  false  ; otherwise * ok is set to  true  .

base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.

The string conversion will always happen in the 'C' locale. For locale dependent conversion use QLocale::toInt ()

QString str = "FF";
bool ok;
int hex = str.toInt(&ok, 16);       // hex == 255, ok == true
int dec = str.toInt(&ok, 10);       // dec == 0, ok == false


QByteArray QString:: toLatin1 () const

Returns a Latin-1 representation of the string as a QByteArray .

The returned byte array is undefined if the string contains non-Latin1 characters. Those characters may be suppressed or replaced with a question mark.

QByteArray QString:: toLocal8Bit () const

Returns the local 8-bit representation of the string as a QByteArray . The returned byte array is undefined if the string contains characters not supported by the local 8-bit encoding.

QTextCodec::codecForLocale () is used to perform the conversion from Unicode. If the locale encoding could not be determined, this function does the same as toLatin1 ().

If this string contains any characters that cannot be encoded in the locale, the returned byte array is undefined. Those characters may be suppressed or replaced by another.

long QString:: toLong ( bool * ok = Q_NULLPTR, int base = 10) const

Returns the string converted to a  long  using base base , which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.

If a conversion error occurs, * ok is set to  false  ; otherwise * ok is set to  true  .

base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.

The string conversion will always happen in the 'C' locale. For locale dependent conversion use QLocale::toLongLong ()

QString str = "FF";
bool ok;
long hex = str.toLong(&ok, 16);     // hex == 255, ok == true
long dec = str.toLong(&ok, 10);     // dec == 0, ok == false


qlonglong QString:: toLongLong ( bool * ok = Q_NULLPTR, int base = 10) const

Returns the string converted to a  long long  using base base , which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.

If a conversion error occurs, * ok is set to  false  ; otherwise * ok is set to  true  .

base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.

The string conversion will always happen in the 'C' locale. For locale dependent conversion use QLocale::toLongLong ()

QString str = "FF";
bool ok;
qint64 hex = str.toLongLong(&ok, 16);      // hex == 255, ok == true
qint64 dec = str.toLongLong(&ok, 10);      // dec == 0, ok == false


QString QString:: toLower () const

Returns a lowercase copy of the string.

QString str = "The Qt PROJECT";
str = str.toLower();        // str == "the qt project"


The case conversion will always happen in the 'C' locale. For locale dependent case folding use QLocale::toLower ()

NSString *QString:: toNSString () const

Creates a NSString from a QString . The NSString is autoreleased.

short QString:: toShort ( bool * ok = Q_NULLPTR, int base = 10) const

Returns the string converted to a  short  using base base , which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.

If a conversion error occurs, * ok is set to  false  ; otherwise * ok is set to  true  .

base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.

The string conversion will always happen in the 'C' locale. For locale dependent conversion use QLocale::toShort ()

QString str = "FF";
bool ok;
short hex = str.toShort(&ok, 16);   // hex == 255, ok == true
short dec = str.toShort(&ok, 10);   // dec == 0, ok == false


std::string QString:: toStdString () const

Returns a std::string object with the data contained in this QString . The Unicode data is converted into 8-bit characters using the toUtf8 () 函数。

This method is mostly useful to pass a QString to a function that accepts a std::string object.

std::u16string QString:: toStdU16String () const

Returns a std::u16string object with the data contained in this QString . The Unicode data is the same as returned by the utf16 () 方法。

std::u32string QString:: toStdU32String () const

Returns a std::u32string object with the data contained in this QString . The Unicode data is the same as returned by the toUcs4 () 方法。

std::wstring QString:: toStdWString () const

This method is mostly useful to pass a QString to a function that accepts a std::wstring 对象。

uint QString:: toUInt ( bool * ok = Q_NULLPTR, int base = 10) const

Returns the string converted to an  无符号 int  using base base , which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.

If a conversion error occurs, * ok is set to  false  ; otherwise * ok is set to  true  .

base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.

The string conversion will always happen in the 'C' locale. For locale dependent conversion use QLocale::toUInt ()

QString str = "FF";
bool ok;
uint hex = str.toUInt(&ok, 16);     // hex == 255, ok == true
uint dec = str.toUInt(&ok, 10);     // dec == 0, ok == false


ulong QString:: toULong ( bool * ok = Q_NULLPTR, int base = 10) const

Returns the string converted to an  unsigned long  using base base , which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.

If a conversion error occurs, * ok is set to  false  ; otherwise * ok is set to  true  .

base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.

The string conversion will always happen in the 'C' locale. For locale dependent conversion use QLocale::toULongLong ()

QString str = "FF";
bool ok;
ulong hex = str.toULong(&ok, 16);   // hex == 255, ok == true
ulong dec = str.toULong(&ok, 10);   // dec == 0, ok == false


qulonglong QString:: toULongLong ( bool * ok = Q_NULLPTR, int base = 10) const

Returns the string converted to an  unsigned long long  using base base , which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.

If a conversion error occurs, * ok is set to  false  ; otherwise * ok is set to  true  .

base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.

The string conversion will always happen in the 'C' locale. For locale dependent conversion use QLocale::toULongLong ()

QString str = "FF";
bool ok;
quint64 hex = str.toULongLong(&ok, 16);    // hex == 255, ok == true
quint64 dec = str.toULongLong(&ok, 10);    // dec == 0, ok == false


ushort QString:: toUShort ( bool * ok = Q_NULLPTR, int base = 10) const

Returns the string converted to an  unsigned short  using base base , which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.

If a conversion error occurs, * ok is set to  false  ; otherwise * ok is set to  true  .

base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.

The string conversion will always happen in the 'C' locale. For locale dependent conversion use QLocale::toUShort ()

QString str = "FF";
bool ok;
ushort hex = str.toUShort(&ok, 16);     // hex == 255, ok == true
ushort dec = str.toUShort(&ok, 10);     // dec == 0, ok == false


QVector < uint > QString:: toUcs4 () const

Returns a UCS-4/UTF-32 representation of the string as a QVector <uint>.

UCS-4 is a Unicode codec and therefore it is lossless. All characters from this string will be encoded in UCS-4. Any invalid sequence of code units in this string is replaced by the Unicode's replacement character ( QChar::ReplacementCharacter , which corresponds to  U+FFFD  ).

The returned vector is not NUL terminated.

QString QString:: toUpper () const

Returns an uppercase copy of the string.

QString str = "TeXt";
str = str.toUpper();        // str == "TEXT"


The case conversion will always happen in the 'C' locale. For locale dependent case folding use QLocale::toUpper ()

QByteArray QString:: toUtf8 () const

Returns a UTF-8 representation of the string as a QByteArray .

UTF-8 is a Unicode codec and can represent all characters in a Unicode string like QString .

int QString:: toWCharArray ( wchar_t * array ) const

Fills the array with the data contained in this QString object. The array is encoded in UTF-16 on platforms where wchar_t is 2 bytes wide (e.g. windows) and in UCS-4 on platforms where wchar_t is 4 bytes wide (most Unix systems).

array has to be allocated by the caller and contain enough space to hold the complete string (allocating the array with the same length as the string is always sufficient).

This function returns the actual length of the string in array .

QString QString:: trimmed () const

Returns a string that has whitespace removed from the start and the end.

Whitespace means any character for which QChar::isSpace () 返回  true  . This includes the ASCII characters '\t', '\n', '\v', '\f', '\r', and ' '.

QString str = "  lots\t of\nwhitespace\r\n ";
str = str.trimmed();
// str == "lots\t of\nwhitespace"


void QString:: truncate ( int position )

Truncates the string at the given position index.

If the specified position index is beyond the end of the string, nothing happens.

QString str = "Vladivostok";
str.truncate(4);


position is negative, it is equivalent to passing zero.

const QChar *QString:: unicode () const

Returns a Unicode representation of the string. The result remains valid until the string is modified.

const ushort *QString:: utf16 () const

The returned string is in host byte order.

 [static]  QString QString:: vasprintf (const char * cformat , va_list ap )

Equivalent method to asprintf (), but takes a va_list ap instead a list of variable arguments. See the asprintf () documentation for an explanation of cformat .

This method does not call the va_end macro, the caller is responsible to call va_end on ap .

bool QString:: operator!= (const char * other ) const

other const char pointer is converted to a QString 使用 fromUtf8 () 函数。

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

bool QString:: operator!= (const QByteArray & other ) const

other byte array is converted to a QString 使用 fromUtf8 () function. If any NUL characters ('\0') are embedded in the byte array, they will be included in the transformation.

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

QString &QString:: operator+= (const QString & other )

Appends the string other onto the end of this string and returns a reference to this string.

QString x = "free";
QString y = "dom";
x += y;
// x == "freedom"


This operation is typically very fast ( constant time ), because QString preallocates extra space at the end of the string data so it can grow without reallocating the entire string each time.

QString &QString:: operator+= ( QChar ch )

Appends the character ch to the string.

QString &QString:: operator+= (const QStringRef & str )

Appends the string section referenced by str to this string.

QString &QString:: operator+= ( QLatin1String str )

Appends the Latin-1 string str to this string.

QString &QString:: operator+= (const char * str )

Appends the string str to this string. The const char pointer is converted to Unicode using the fromUtf8 () 函数。

You can disable this function by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

QString &QString:: operator+= (const QByteArray & ba )

Appends the byte array ba to this string. The byte array is converted to Unicode using the fromUtf8 () function. If any NUL characters ('\0') are embedded in the ba byte array, they will be included in the transformation.

You can disable this function by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

QString &QString:: operator+= ( char ch )

Appends the character ch to this string. Note that the character is converted to Unicode using the fromLatin1 () function, unlike other 8-bit functions that operate on UTF-8 data.

You can disable this function by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

bool QString:: operator< (const char * other ) const

other const char pointer is converted to a QString 使用 fromUtf8 () 函数。

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

bool QString:: operator< (const QByteArray & other ) const

other byte array is converted to a QString 使用 fromUtf8 () function. If any NUL characters ('\0') are embedded in the byte array, they will be included in the transformation.

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

bool QString:: operator<= (const char * other ) const

other const char pointer is converted to a QString 使用 fromUtf8 () 函数。

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

bool QString:: operator<= (const QByteArray & other ) const

other byte array is converted to a QString 使用 fromUtf8 () function. If any NUL characters ('\0') are embedded in the byte array, they will be included in the transformation.

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

QString &QString:: operator= ( QChar ch )

Sets the string to contain the single character ch .

QString &QString:: operator= ( QLatin1String str )

Assigns the Latin-1 string str to this string.

QString &QString:: operator= (const char * str )

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  or  QT_RESTRICTED_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

QString &QString:: operator= (const QByteArray & ba )

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

QString &QString:: operator= ( char ch )

Assigns character ch to this string. Note that the character is converted to Unicode using the fromLatin1 () function, unlike other 8-bit functions that operate on UTF-8 data.

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

bool QString:: operator== (const char * other ) const

other const char pointer is converted to a QString 使用 fromUtf8 () 函数。

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

bool QString:: operator== (const QByteArray & other ) const

other byte array is converted to a QString 使用 fromUtf8 () function. This function stops conversion at the first NUL character found, or the end of the byte array.

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

bool QString:: operator> (const char * other ) const

other const char pointer is converted to a QString 使用 fromUtf8 () 函数。

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

bool QString:: operator> (const QByteArray & other ) const

other byte array is converted to a QString 使用 fromUtf8 () function. If any NUL characters ('\0') are embedded in the byte array, they will be included in the transformation.

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

bool QString:: operator>= (const char * other ) const

other const char pointer is converted to a QString 使用 fromUtf8 () 函数。

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

bool QString:: operator>= (const QByteArray & other ) const

other byte array is converted to a QString 使用 fromUtf8 () function. If any NUL characters ('\0') are embedded in the byte array, they will be included in the transformation.

You can disable this operator by defining  QT_NO_CAST_FROM_ASCII  when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

QCharRef QString:: operator[] ( int position )

Returns the character at the specified position in the string as a modifiable reference.

QString str;
if (str[0] == QChar('?'))
str[0] = QChar('_');


The return value is of type QCharRef, a helper class for QString . When you get an object of type QCharRef, you can use it as if it were a QChar &. If you assign to it, the assignment will apply to the character in the QString from which you got the reference.

QCharRef QString:: operator[] ( uint position )

Returns the character at the specified position in the string as a modifiable reference.

相关非成员

bool operator!= (const QString & s1 , const QString & s2 )

The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with localeAwareCompare().

bool operator!= (const char * s1 , const QString & s2 )

For s1 != 0, this is equivalent to  compare(  s1 , s2  ) != 0  . Note that no string is equal to s1 being 0.

const QString operator+ (const QString & s1 , const QString & s2 )

Returns a string which is the result of concatenating s1 and s2 .

const QString operator+ (const QString & s1 , const char * s2 )

Returns a string which is the result of concatenating s1 and s2 ( s2 is converted to Unicode using the QString::fromUtf8 () function).

const QString operator+ (const char * s1 , const QString & s2 )

Returns a string which is the result of concatenating s1 and s2 ( s1 is converted to Unicode using the QString::fromUtf8 () function).

const QString operator+ (const QString & s , char ch )

Returns a string which is the result of concatenating the string s and the character ch .

const QString operator+ ( char ch , const QString & s )

Returns a string which is the result of concatenating the character ch and the string s .

bool operator< (const char * s1 , const QString & s2 )

The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings using the QString::localeAwareCompare () 函数。

bool operator<= (const QString & s1 , const QString & s2 )

The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with localeAwareCompare().

bool operator<= (const char * s1 , const QString & s2 )

The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with QString::localeAwareCompare ().

bool operator> (const QString & s1 , const QString & s2 )

The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with localeAwareCompare().

bool operator> (const char * s1 , const QString & s2 )

The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings using the QString::localeAwareCompare () 函数。

bool operator>= (const QString & s1 , const QString & s2 )

The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with localeAwareCompare().

bool operator>= (const char * s1 , const QString & s2 )

The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings using the QString::localeAwareCompare () 函数。

QDataStream & operator>> ( QDataStream & stream , QString & string )

Reads a string from the specified stream 进给定 string .

宏文档编制

QStringLiteral ( str )

The macro generates the data for a QString out of the string literal str at compile time. Creating a QString from it is free in this case, and the generated string data is stored in the read-only segment of the compiled object file.

If you have code that looks like this:

// hasAttribute takes a QString argument
if (node.hasAttribute("http-contents-length")) //...


then a temporary QString will be created to be passed as the  hasAttribute  function parameter. This can be quite expensive, as it involves a memory allocation and the copy/conversion of the data into QString 's internal encoding.

This cost can be avoided by using QStringLiteral instead:

if (node.hasAttribute(QStringLiteral(u"http-contents-length"))) //...


In this case, QString 's internal data will be generated at compile time; no conversion or allocation will occur at runtime.

Using QStringLiteral instead of a double quoted plain C++ string literal can significantly speed up creation of QString instances from data known at compile time.

if (attribute.name() == QLatin1String("http-contents-length")) //...


QT_NO_CAST_FROM_ASCII

Disables automatic conversions from 8-bit strings (char *) to unicode QStrings

QT_NO_CAST_TO_ASCII

disables automatic conversion from QString to 8-bit strings (char *)

QT_RESTRICTED_CAST_FROM_ASCII

Defining this macro disables most automatic conversions from source literals and 8-bit data to unicode QStrings, but allows the use of the  QChar(char)  and  QString(const char (&ch)[N]  constructors, and the  QString::operator=(const char (&ch)[N])  assignment operator giving most of the type-safety benefits of QT_NO_CAST_FROM_ASCII but does not require user code to wrap character and string literals with QLatin1Char , QLatin1String or similar.

Using this macro together with source strings outside the 7-bit range, non-literals, or literals with embedded NUL characters is undefined.