QString 類

QString 類提供 Unicode 字符串。 更多...

• 所有成員列錶，包括繼承成員
• 過時成員

注意： 此類的所有函數 可重入 .

公共類型

公共函數

靜態公共成員

相關非成員

宏

詳細描述

QString 存儲字符串的 16 位 QChar ，其中各 QChar corresponds to one UTF-16 code unit. (Unicode characters with code values above 65535 are stored using surrogate pairs, i.e., two consecutive QChar )。

Unicode 是支持當今使用的大多數書寫係統的國際標準。它是 US-ASCII (ANSI X3.4-1986) 和 Latin-1 (ISO 8859-1) 的超集，且所有 US-ASCII/Latin-1 字符可用於相同代碼位置。

在幕後，QString 使用 隱式共享 (寫時拷貝) 以縮減內存用量並避免不必要的數據拷貝。這還有助於縮減存儲 16 位字符而不是 8 位字符的固有開銷。

除 QString 外，Qt 還提供 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 是閤適的，當需要存儲原生二進製數據時，和當內存守恒臨界時 (像在嵌入式係統)。

初始化字符串

One way to initialize a QString is simply to pass a const char * 到其構造函數。例如，以下代碼創建包含數據 Hello 大小為 5 的 QString：

QString str = "Hello";
					

QString 轉換 const char * 數據成 Unicode 使用 fromUtf8 () 函數。

QString 的所有函數都接受 const char * 參數， 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 nullptr .

還可以將字符串數據提供成數組化的 QChar ：

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

QString 製作深拷貝對 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.)

另一種方式是設置字符串大小使用 resize () 並逐字符初始化數據。QString 使用基於 0 的索引，就像 C++ 數組。要訪問位於特定索引位置的字符，可以使用 operator[] (). On non-const strings, operator[] () 返迴可以用於賦值左側的字符引用。例如：

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

對於隻讀訪問，替代句法是使用 at () 函數：

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]";
}
					

The at () 函數可以更快相比 operator[] (), because it never causes a 深拷貝 的齣現。另外，使用 left (), right ()，或 mid () 函數能一次提取幾個字符。

QString 可以嵌入 \0 字符 ( QChar::Null )。 size () 函數始終返迴整個字符串的大小，包括嵌入 \0 字符。

後於調用 resize () 函數，新近分配字符擁有未定義值。要把字符串中的所有字符設為特定值，使用 fill () 函數。

QString 提供瞭很多設計用於簡化字符串用法的重載。例如，若想要比較 QString 與字符串文字，可以像這樣編寫代碼且它會如期望般工作：

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

還可以把字符串文字傳遞給接受 QString 作為自變量的函數，援引 QString(const char *) 構造函數。同樣，可以傳遞 QString 的函數接受 const char * 自變量使用 qPrintable () macro which returns the given QString as a const char * 。這相當於調用 <QString>. toLocal8Bit (). constData ().

操縱字符串數據

QString 提供修改字符數據的基本功能： 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"
					

若正逐步構建 QString 且提前大概知道 QString 將包含多少個字符，可以調用 reserve ()，要求 QString 預分配一定數量的內存。也可以調用 capacity () to find out how much memory QString actually allocated.

The 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 ().

若想要查找 QString 中的特定字符 (或子字符串) 的所有齣現，使用 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 is 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 提供瞭很多按數字轉換成字符串，和把字符串轉換成數字的函數。見 arg () 函數， setNum () 函數， number () 靜態函數，和 toInt (), toDouble ()，及類似函數。

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

字符串列錶的處理是通過 QStringList 類。可以把字符串分割成字符串列錶使用 split () 函數，和把字符串列錶聯接成單字符串采用可選分隔符使用 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 () 函數。

查詢字符串數據

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 ().

要獲得實際字符數據指針，調用 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.

Comparing Strings

可以比較 QString 使用重載運算符譬如 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 usually a better choice for sorting user-interface strings, when such a comparison is available.

On Unix-like platforms (including Linux, macOS and iOS), when Qt is linked with the ICU library (which it usually is), its locale-aware sorting is used. Otherwise, on macOS and iOS, localeAwareCompare () compares according the "Order for sorted lists" setting in the International preferences panel. On other Unix-like systems without ICU, the comparison falls back to the system library's strcoll() , falling back when it considers strings equal to QString's (locale-unaware) comparison, described above,

在 8 位字符串和 Unicode 字符串之間轉換

QString provides the following three functions that return a const char * 版本的字符串如 QByteArray : toUtf8 (), toLatin1 ()，和 toLocal8Bit ().

• toLatin1 () 返迴 Latin-1 (ISO 8859-1) 編碼 8 位字符串。
• toUtf8 () 返迴 UTF-8 編碼 8 位字符串。UTF-8 是 US-ASCII (ANSI X3.4-1986) 超集，支持透過多字節序列的整個 Unicode 字符集。
• toLocal8Bit () returns an 8-bit string using the system's local encoding.

要轉換自這些編碼之一，QString 提供 fromLatin1 (), fromUtf8 ()，和 fromLocal8Bit ()。其它編碼的支持是透過 QTextCodec 類。

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 some of the following 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.

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/");
					

同樣，必須調用 toLatin1 (), toUtf8 ()，或 toLocal8Bit () explicitly to convert the QString to an 8-bit string. (Other encodings are supported through the QTextCodec class.)

QString Widget::boolToString(bool b)
{


QString


 result;

if

 (b)
result

=


"True"

;

else

result

=


"False"

;

return

 result;
}
								

null 和空字符串之間的區彆

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
					

所有函數除瞭 isNull () treat null strings the same as empty strings. For example, toUtf8 (). constData () returns a valid pointer ( not nullptr) to a '\0' character for a null string. We recommend that you always use the isEmpty () function and avoid isNull ().

自變量格式

成員函數中的自變量 format 可以指定 (如： arg (), number ())，自變量 format can be one of the following:

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).

更高效的字符串構造

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.

使用 QString '+' operator, it is easy to construct a complex string from multiple substrings. You will often write code like this:

    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 () 需要額外測試)。

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 '%' 運算符而不是 '+' 當串聯字符串時：

    #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
					

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

最大尺寸和內存不足情況

The current version of QString is limited to just under 2 GB (2^31 bytes) in size. The exact value is architecture-dependent, since it depends on the overhead required for managing the data block, but is no more than 32 bytes. Raw data blocks are also limited by the use of int type in the current version to 2 GB minus 1 byte. Since QString uses two bytes per character, that translates to just under 2^30 characters in one QString.

In case memory allocation fails, QString will throw a std::bad_alloc exception. Out of memory conditions in the Qt containers are the only case where Qt will throw exceptions.

Note that the operating system may impose further limits on applications holding a lot of allocated memory, especially large, contiguous blocks. Such considerations, the configuration of such behavior or any mitigation are outside the scope of the Qt API.

另請參閱 fromRawData (), QChar , QLatin1String , QByteArray ，和 QStringRef .

成員類型文檔編製

typedef QString:: ConstIterator

Qt 樣式同義詞 QString::const_iterator .

typedef QString:: Iterator

Qt 樣式同義詞 QString::iterator .

enum QString:: NormalizationForm

此枚舉描述 Unicode 文本的各種規範化形式。

另請參閱 normalized () 和 Unicode 標準附錄 #15 .

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.

SectionFlags 類型是 typedef 對於 QFlags <SectionFlag>. It stores an OR combination of SectionFlag values.

另請參閱 section ().

typedef QString:: const_iterator

另請參閱 QString::iterator .

typedef QString:: const_pointer

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

typedef QString:: const_reference

typedef QString:: const_reverse_iterator

該 typedef 在 Qt 5.6 引入。

另請參閱 QString::reverse_iterator and QString::const_iterator .

typedef QString:: difference_type

typedef QString:: iterator

另請參閱 QString::const_iterator .

typedef QString:: pointer

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

typedef QString:: reference

typedef QString:: reverse_iterator

該 typedef 在 Qt 5.6 引入。

另請參閱 QString::const_reverse_iterator and QString::iterator .

typedef QString:: size_type

typedef QString:: value_type

成員函數文檔編製

template <typename Args> QString QString:: arg ( Args &&... args ) const

Replaces occurrences of %N in this string with the corresponding argument from args . The arguments are not positional: the first of the args 替換 %N with the lowest N (all of them), the second of the args the %N with the next-lowest N etc.

Args can consist of anything that implicitly converts to QString , QStringView or QLatin1String .

In addition, the following types are also supported: QChar , QLatin1Char .

該函數在 Qt 5.14 引入。

另請參閱 QString::arg ().

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.

另請參閱 fromLatin1 (), fromLocal8Bit (), fromUtf8 ()，和 QT_NO_CAST_FROM_ASCII .

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 () 函數。

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.

注意： Defining QT_RESTRICTED_CAST_FROM_ASCII also disables this constructor, but enables a QString(const char (&ch)[N]) constructor instead. Using non-literal input, or input with embedded NUL characters, or non-7-bit characters is undefined in this case.

另請參閱 fromLatin1 (), fromLocal8Bit (), fromUtf8 (), QT_NO_CAST_FROM_ASCII ，和 QT_RESTRICTED_CAST_FROM_ASCII .

QString:: QString ( QString && other )

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

該函數在 Qt 5.2 引入。

QString:: QString (const QString & other )

構造副本為 other .

此操作花費 常量時間 ，因為 QString 是 隱式共享 . 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 綫性時間 .

另請參閱 operator= ().

QString:: QString ( QLatin1String str )

Constructs a copy of the Latin-1 string str .

另請參閱 fromLatin1 ().

QString:: QString ( int size , QChar ch )

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

另請參閱 fill ().

QString:: QString ( QChar ch )

Constructs a string of size 1 containing the character ch .

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

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

若 unicode 為 0，構造 null 字符串。

若 size 為負， unicode is assumed to point to a \0'-terminated array and its length is determined dynamically. The terminating null 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.

另請參閱 fromRawData ().

QString:: QString ()

Constructs a null string. Null strings are also empty.

另請參閱 isEmpty ().

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

此函數重載 operator=()。

賦值 ba to this string. The byte array is converted to Unicode using the fromUtf8 () function. This function stops conversion at the first NUL character found, or the end of the ba byte array.

可以禁用此運算符通過定義 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.

另請參閱 QT_NO_CAST_FROM_ASCII .

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

移動賦值 other 到此 QString 實例。

該函數在 Qt 5.2 引入。

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

賦值 other to this string and returns a reference to this string.

QString:: ~QString ()

銷毀字符串。

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

追加字符串 str 到此字符串末尾。

範例：

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

這如同使用 insert () 函數：

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

append() 函數通常非常快 ( 常量時間 )，因為 QString preallocates extra space at the end of the string data so it can grow without reallocating the entire string each time.

另請參閱 operator+= (), prepend ()，和 insert ().

QString &QString:: append ( QChar ch )

此函數重載 append()。

追加字符 ch 到此字符串。

QString &QString:: append (const QChar * str , int len )

此函數重載 append()。

追加 len 字符來自 QChar array str 到此字符串。

該函數在 Qt 5.0 引入。

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

追加給定字符串 reference to this string and returns the result.

該函數在 Qt 4.4 引入。

QString &QString:: append ( QLatin1String str )

此函數重載 append()。

追加 Latin-1 字符串 str 到此字符串。

QString &QString:: append ( QStringView str )

追加給定字符串 str to this string and returns the result.

注意： This method has been added in 5.15.2 to simplify writing code that is portable between Qt 5.15 and Qt 6.

This function was introduced in Qt 5.15.2.

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

此函數重載 append()。

追加字符串 str to this string. The given const char pointer is converted to Unicode using the fromUtf8 () 函數。

可以禁用此函數通過定義 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.

另請參閱 QT_NO_CAST_FROM_ASCII .

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

此函數重載 append()。

追加字節數組 ba to this string. The given byte array is converted to Unicode using the fromUtf8 () 函數。

可以禁用此函數通過定義 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.

另請參閱 QT_NO_CAST_FROM_ASCII .

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

返迴字符串副本，替換最小編號位置標記為字符串 a ，即： %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.

此範例展示如何創建 status 字符串為處理文件列錶時報告進度：

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);
					

首先， arg(i) 替換 %1 。然後 arg(total) 替換 %2 。最後， arg(fileName) 替換 %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 ( qlonglong a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const

此函數重載 arg()。

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 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.

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

此函數重載 arg()。

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 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.

若 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

此函數重載 arg()。

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 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"
					

若 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

此函數重載 arg()。

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 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.

若 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

此函數重載 arg()。

The 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"
					

若 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

此函數重載 arg()。

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

若 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

此函數重載 arg()。

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 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.

若 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

此函數重載 arg()。

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 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.

若 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

此函數重載 arg()。

自變量 a is formatted according to the specified format and precision 。見 自變量格式 瞭解細節。

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.

若 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.

另請參閱 QLocale::toString ().

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

此函數重載 arg()。

The a 自變量被解釋成 Latin-1 字符。

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

此函數重載 arg()。

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

這是重載函數。

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

fieldWidth specifies the minimum amount of space that 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.

此範例展示如何創建 status 字符串為處理文件列錶時報告進度：

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

首先， arg(i) 替換 %1 。然後 arg(total) 替換 %2 。最後， arg(fileName) 替換 %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, arg() replaces all of them.

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

該函數在 Qt 5.10 引入。

QString QString:: arg ( QLatin1String a , int fieldWidth = 0, QChar fillChar = QLatin1Char(' ')) const

這是重載函數。

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

fieldWidth specifies the minimum amount of space that 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.

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, arg() replaces all of them.

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

該函數在 Qt 5.10 引入。

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

此函數重載 arg()。

這如同 str.arg(a1).arg(a2) , except that the strings a1 and a2 are replaced in one pass. This can make a difference if a1 contains e.g. %1 :

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:

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

Thus the string finally becomes "Hello500" .

In such cases, the following yields the expected results:

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

QString QString:: arg (const QString & a1 , const QString & a2 , const QString & a3 ) const

此函數重載 arg()。

這如同調用 str.arg(a1).arg(a2).arg(a3) , except that the strings a1 , a2 and a3 are replaced in one pass.

QString QString:: arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 ) const

此函數重載 arg()。

這如同調用 str.arg(a1).arg(a2).arg(a3).arg(a4) , except that the strings a1 , a2 , a3 and a4 are replaced in one pass.

QString QString:: arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 , const QString & a5 ) const

此函數重載 arg()。

這如同調用 str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5) , except that the strings a1 , a2 , a3 , a4 ，和 a5 are replaced in one pass.

QString QString:: arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 , const QString & a5 , const QString & a6 ) const

此函數重載 arg()。

這如同調用 str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5).arg(a6)) , except that the strings a1 , a2 , a3 , a4 , a5 ，和 a6 are replaced in one pass.

QString QString:: arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 , const QString & a5 , const QString & a6 , const QString & a7 ) const

此函數重載 arg()。

這如同調用 str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5).arg(a6).arg(a7) , except that the strings a1 , a2 , a3 , a4 , a5 , a6 ，和 a7 are replaced in one pass.

QString 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

此函數重載 arg()。

這如同調用 str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5).arg(a6).arg(a7).arg(a8) , except that the strings a1 , a2 , a3 , a4 , a5 , a6 , a7 ，和 a8 are replaced in one pass.

QString 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

此函數重載 arg()。

這如同調用 str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5).arg(a6).arg(a7).arg(a8).arg(a9) , except that the strings a1 , a2 , a3 , a4 , a5 , a6 , a7 , a8 ，和 a9 are replaced in one pass.

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

安全地構建格式化字符串從格式字符串 cformat 和任意自變量列錶。

格式字符串支持轉換說明符、長度修飾符及由標準 C++ 庫 printf() 提供的標誌。 cformat 字符串和 %s 自變量必須是 UTF-8 編碼。

注意： The %lc 轉義序列期望 unicode 字符類型為 char16_t ，或 ushort (如返迴通過 QChar::unicode ())。 %ls 轉義序列期望的指針指嚮以 0 結尾的數組的 Unicode 字符類型為 char16_t ，或 ushort (如返迴通過 QString::utf16 ())。這與標準 C++ 庫 printf() 不一緻，後者定義的 %lc 會打印 wchar_t 而 %ls 會打印 wchar_t* ，且平颱還可能産生編譯器警告，若大小請考慮使用請考慮使用請考慮使用請考慮使用請考考慮 wchar_t 不是 16 位。

警告： 不推薦在新 Qt 代碼中使用 QString::asprintf()。取而代之，考慮使用 QTextStream or arg ()，兩者無縫支持 Unicode 字符串且是類型安全的。這裏的範例使用 QTextStream :

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

For translations ，尤其當字符串包含多個轉義序列時，應考慮使用 arg () 函數代替。這允許翻譯者控製置換次序。

該函數在 Qt 5.5 引入。

另請參閱 arg ().

const QChar QString:: at ( int position ) const

返迴字符按給定索引 position 在字符串中。

The position 在字符串中必須是有效索引位置 (即 0 <= position < size ()).

另請參閱 operator[] ().

QChar QString:: back () const

返迴字符串中的最後一個字符。如同 at(size() - 1) .

此函數為兼容 STL (標準模闆庫) 提供。

警告： 在空字符串調用此函數，將構成未定義行為。

該函數在 Qt 5.10 引入。

另請參閱 front (), at ()，和 operator[] ().

QCharRef QString:: back ()

Returns a reference to the last character in the string. Same as operator[](size() - 1) .

此函數為兼容 STL (標準模闆庫) 提供。

警告： 在空字符串調用此函數，將構成未定義行為。

該函數在 Qt 5.10 引入。

另請參閱 front (), at ()，和 operator[] ().

QString::iterator QString:: begin ()

返迴 STL 樣式迭代器 指嚮字符串中的首個字符。

另請參閱 constBegin () 和 end ().

QString::const_iterator QString:: begin () const

此函數重載 begin()。

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 ().

另請參閱 reserve () 和 squeeze ().

QString::const_iterator QString:: cbegin () const

返迴常量 STL 樣式迭代器 指嚮字符串中的首個字符。

該函數在 Qt 5.0 引入。

另請參閱 begin () 和 cend ().

QString::const_iterator QString:: cend () const

返迴常量 STL 樣式迭代器 pointing to the imaginary character after the last character in the list.

該函數在 Qt 5.0 引入。

另請參閱 cbegin () 和 end ().

void QString:: chop ( int n )

移除 n 個字符從字符串末尾起。

若 n >= size ()，結果為空字符串；若 n 為負，相當於傳遞 0。

範例：

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

若想要移除字符從 beginning 對於字符串，使用 remove () 代替。

另請參閱 truncate (), resize (), remove ()，和 QStringRef::chop ().

QString QString:: chopped ( int len ) const

Returns a substring that contains the size () - len leftmost characters of this string.

注意： 行為未定義若 len 為負或大於 size ().

該函數在 Qt 5.10 引入。

另請參閱 endsWith (), left (), right (), mid (), chop ()，和 truncate ().

void QString:: clear ()

清零字符串內容，並使之為 null。

另請參閱 resize () 和 isNull ().

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

比較 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 .

若 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
					

該函數在 Qt 4.2 引入。

另請參閱 operator== (), operator< (), operator> ()，和 Comparing Strings .

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

此函數重載 compare()。

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.

如同 compare(*this, other , cs ).

該函數在 Qt 4.2 引入。

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

此函數重載 compare()。

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 .

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

此函數重載 compare()。

如同 compare(*this, other , cs ).

該函數在 Qt 4.2 引入。

int QString:: compare ( QStringView s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 compare()。

履行比較為此與 s ，使用區分大小寫設置 cs .

該函數在 Qt 5.12 引入。

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

此函數重載 compare()。

履行比較為此與 ch ，使用區分大小寫設置 cs .

該函數在 Qt 5.14 引入。

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

此函數重載 compare()。

履行比較為 s1 and s2 ，使用區分大小寫設置 cs .

該函數在 Qt 4.2 引入。

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

此函數重載 compare()。

履行比較為 s1 and s2 ，使用區分大小寫設置 cs .

該函數在 Qt 4.2 引入。

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

此函數重載 compare()。

QString::const_iterator QString:: constBegin () const

返迴常量 STL 樣式迭代器 指嚮字符串中的首個字符。

另請參閱 begin () 和 constEnd ().

const QChar *QString:: constData () const

返迴指針指嚮的數據存儲在 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.

注意： 返迴字符串不能以 \0 結尾。使用 size () 以確定數組的長度。

另請參閱 data (), operator[] ()，和 fromRawData ().

QString::const_iterator QString:: constEnd () const

返迴常量 STL 樣式迭代器 pointing to the imaginary character after the last character in the list.

另請參閱 constBegin () 和 end ().

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

返迴 true 若此字符串包含齣現的字符串 str ；否則返迴 false .

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

範例：

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

另請參閱 indexOf () 和 count ().

bool QString:: contains ( QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 contains()。

返迴 true 若此字符串包含齣現字符 ch ；否則返迴 false .

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

返迴 true if this string contains an occurrence of the string reference str ；否則返迴 false .

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

該函數在 Qt 4.8 引入。

另請參閱 indexOf () 和 count ().

bool QString:: contains ( QLatin1String str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 contains()。

返迴 true 若此字符串包含齣現的 latin-1 字符串 str ；否則返迴 false .

該函數在 Qt 5.3 引入。

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

此函數重載 contains()。

返迴 true 若此字符串包含齣現的字符串視圖 str ；否則返迴 false .

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

該函數在 Qt 5.14 引入。

另請參閱 indexOf () 和 count ().

bool QString:: contains (const QRegExp & rx ) const

此函數重載 contains()。

返迴 true 若正則錶達式 rx 匹配此字符串中的某些地方；否則返迴 false .

bool QString:: contains ( QRegExp & rx ) const

此函數重載 contains()。

返迴 true 若正則錶達式 rx 匹配此字符串中的某些地方；否則返迴 false .

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

該函數在 Qt 4.5 引入。

bool QString:: contains (const QRegularExpression & re ) const

此函數重載 contains()。

返迴 true 若正則錶達式 re 匹配此字符串中的某些地方；否則返迴 false .

該函數在 Qt 5.0 引入。

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

此函數重載 contains()。

返迴 true 若正則錶達式 re 匹配此字符串中的某些地方；否則返迴 false .

若匹配成功且 rmatch 不是 nullptr ，它還把匹配結果寫入 QRegularExpressionMatch 對象指嚮的 rmatch .

該函數在 Qt 5.1 引入。

另請參閱 QRegularExpression::match ().

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

返迴 (潛在重疊) 齣現數對於字符串 str 在此字符串中。

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

另請參閱 contains () 和 indexOf ().

int QString:: count () const

此函數重載 count()。

如同 size ().

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

此函數重載 count()。

返迴齣現數對於字符 ch 在字符串中。

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

另請參閱 contains () 和 indexOf ().

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

此函數重載 count()。

Returns the number of (potentially overlapping) occurrences of the string reference str 在此字符串中。

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

該函數在 Qt 4.8 引入。

另請參閱 contains () 和 indexOf ().

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

此函數重載 count()。

返迴次數對於正則錶達式 rx 匹配在字符串中。

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

此函數重載 count()。

返迴次數對於正則錶達式 re 匹配在字符串中。

由於曆史原因，此函數計算重疊匹配，因此下文範例有 4 個 ana 或 ama 實例：

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

此行為不同於簡單遍曆字符串中的匹配使用 QRegularExpressionMatchIterator .

該函數在 Qt 5.0 引入。

另請參閱 QRegularExpression::globalMatch ().

QString::const_reverse_iterator QString:: crbegin () const

返迴常量 STL-style reverse iterator pointing to the first character in the string, in reverse order.

該函數在 Qt 5.6 引入。

另請參閱 begin (), rbegin ()，和 rend ().

QString::const_reverse_iterator QString:: crend () const

返迴常量 STL-style reverse iterator pointing to one past the last character in the string, in reverse order.

該函數在 Qt 5.6 引入。

另請參閱 end (), rend ()，和 rbegin ().

QChar *QString:: data ()

返迴指針指嚮的數據存儲在 QString . The pointer can be used to access and modify the characters that compose the string.

不像 constData () 和 unicode ()，返迴數據始終以 \0 結尾。

範例：

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 () 更快，因為它從不導緻 深拷貝 的齣現。

另請參閱 constData () 和 operator[] ().

const QChar *QString:: data () const

這是重載函數。

注意： 返迴字符串不能以 \0 結尾。使用 size () 以確定數組的長度。

另請參閱 fromRawData ().

QString::iterator QString:: end ()

返迴 STL 樣式迭代器 pointing to the imaginary character after the last character in the string.

另請參閱 begin () 和 constEnd ().

QString::const_iterator QString:: end () const

此函數重載 end()。

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

返迴 true 若字符串結尾為 s ；否則返迴 false .

若 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
					

另請參閱 startsWith ().

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

此函數重載 endsWith()。

返迴 true if the string ends with the string reference s ；否則返迴 false .

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

該函數在 Qt 4.8 引入。

另請參閱 startsWith ().

bool QString:: endsWith ( QStringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 endsWith()。

返迴 true 若字符串結尾為字符串視圖 str ；否則返迴 false .

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

該函數在 Qt 5.10 引入。

另請參閱 startsWith ().

bool QString:: endsWith ( QLatin1String s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 endsWith()。

bool QString:: endsWith ( QChar c , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

返迴 true 若字符串結尾為 c ；否則返迴 false .

此函數重載 endsWith()。

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

將字符串中的每個字符設為字符 ch 。若 size 不同於 -1 (默認)，重置字符串大小到 size 事先。

範例：

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

另請參閱 resize ().

[static] QString QString:: fromCFString ( CFStringRef string )

構造新的 QString 包含副本 string CFString.

注意： this function is only available on OS X and iOS.

該函數在 Qt 5.2 引入。

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

返迴 QString 初始采用前 size characters of the Latin-1 string str .

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

另請參閱 toLatin1 (), fromUtf8 ()，和 fromLocal8Bit ().

[static] QString QString:: fromLatin1 (const QByteArray & str )

這是重載函數。

返迴 QString 初始采用 Latin-1 字符串 str .

該函數在 Qt 5.0 引入。

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

返迴 QString 初始采用前 size 個字符對於 8 位字符串 str .

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

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

另請參閱 toLocal8Bit (), fromLatin1 ()，和 fromUtf8 ().

[static] QString QString:: fromLocal8Bit (const QByteArray & str )

這是重載函數。

返迴 QString initialized with the 8-bit string str .

該函數在 Qt 5.0 引入。

[static] QString QString:: fromNSString (const NSString * string )

構造新的 QString 包含副本 string NSString.

注意： this function is only available on OS X and iOS.

該函數在 Qt 5.2 引入。

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

構造 QString that uses 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.

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 is 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) {
    // ...
}
					

警告： A string created with fromRawData() is not '\0'-terminated, unless the raw data contains a '\0' character at position size 。這意味著 unicode () will not return a '\0'-terminated string (although utf16 () does, at the cost of copying the raw data).

另請參閱 fromUtf16 () 和 setRawData ().

[static] QString QString:: fromStdString (const std::string & str )

返迴副本為 str string. The given string is converted to Unicode using the fromUtf8 () 函數。

另請參閱 fromLatin1 (), fromLocal8Bit (), fromUtf8 ()，和 QByteArray::fromStdString ().

[static] QString QString:: fromStdU16String (const std::u16string & str )

返迴副本為 str string. The given string is assumed to be encoded in UTF-16.

該函數在 Qt 5.5 引入。

另請參閱 fromUtf16 (), fromStdWString ()，和 fromStdU32String ().

[static] QString QString:: fromStdU32String (const std::u32string & str )

返迴副本為 str string. The given string is assumed to be encoded in UCS-4.

該函數在 Qt 5.5 引入。

另請參閱 fromUcs4 (), fromStdWString ()，和 fromStdU16String ().

[static] QString QString:: fromStdWString (const std::wstring & str )

返迴副本為 str string. The given string is assumed to be encoded in utf16 if the size of wchar_t is 2 bytes (e.g. on windows) and ucs4 if the size of wchar_t is 4 bytes (most Unix systems).

另請參閱 fromUtf16 (), fromLatin1 (), fromLocal8Bit (), fromUtf8 (), fromUcs4 (), fromStdU16String ()，和 fromStdU32String ().

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

返迴 QString 初始采用前 size characters of the Unicode string unicode (ISO-10646-UCS-4 encoded).

若 size is -1 (default), unicode must be \0'-terminated.

該函數在 Qt 4.2 引入。

另請參閱 toUcs4 (), fromUtf16 (), utf16 (), setUtf16 (), fromWCharArray ()，和 fromStdU32String ().

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

返迴 QString 初始采用前 size characters of the Unicode string str (ISO-10646-UCS-4 encoded).

若 size is -1 (default), str must be \0'-terminated.

該函數在 Qt 5.3 引入。

另請參閱 toUcs4 (), fromUtf16 (), utf16 (), setUtf16 (), fromWCharArray ()，和 fromStdU32String ().

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

返迴 QString 初始采用前 size bytes of the UTF-8 string str .

若 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 .

另請參閱 toUtf8 (), fromLatin1 ()，和 fromLocal8Bit ().

[static] QString QString:: fromUtf8 (const QByteArray & str )

這是重載函數。

返迴 QString initialized with the UTF-8 string str .

該函數在 Qt 5.0 引入。

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

返迴 QString 初始采用前 size characters of the Unicode string unicode (ISO-10646-UTF-16 encoded).

若 size is -1 (default), unicode must be \0'-terminated.

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.

另請參閱 utf16 (), setUtf16 ()，和 fromStdU16String ().

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

返迴 QString 初始采用前 size characters of the Unicode string str (ISO-10646-UTF-16 encoded).

若 size is -1 (default), str must be \0'-terminated.

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.

該函數在 Qt 5.3 引入。

另請參閱 utf16 (), setUtf16 ()，和 fromStdU16String ().

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

返迴副本為 string , where the encoding of string depends on the size of wchar. If wchar is 4 bytes, the string is interpreted as UCS-4, if wchar is 2 bytes it is interpreted as UTF-16.

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

該函數在 Qt 4.2 引入。

另請參閱 fromUtf16 (), fromLatin1 (), fromLocal8Bit (), fromUtf8 (), fromUcs4 ()，和 fromStdWString ().

QChar QString:: front () const

Returns the first character in the string. Same as at(0) .

此函數為兼容 STL (標準模闆庫) 提供。

警告： 在空字符串調用此函數，將構成未定義行為。

該函數在 Qt 5.10 引入。

另請參閱 back (), at ()，和 operator[] ().

QCharRef QString:: front ()

Returns a reference to the first character in the string. Same as operator[](0) .

此函數為兼容 STL (標準模闆庫) 提供。

警告： 在空字符串調用此函數，將構成未定義行為。

該函數在 Qt 5.10 引入。

另請參閱 back (), at ()，和 operator[] ().

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。

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

範例：

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
					

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

該函數在 Qt 4.5 引入。

另請參閱 lastIndexOf (), contains ()，和 count ().

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

此函數重載 indexOf()。

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 (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。

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

範例：

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
					

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

另請參閱 lastIndexOf (), contains ()，和 count ().

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

此函數重載 indexOf()。

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。

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

該函數在 Qt 4.8 引入。

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

此函數重載 indexOf()。

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

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

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

該函數在 Qt 5.14 引入。

另請參閱 QStringView::indexOf (), lastIndexOf (), contains ()，和 count ().

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

此函數重載 indexOf()。

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.

範例：

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

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

此函數重載 indexOf()。

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 ).

範例：

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

該函數在 Qt 4.5 引入。

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

此函數重載 indexOf()。

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.

範例：

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

該函數在 Qt 5.0 引入。

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

這是重載函數。

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.

若匹配成功且 rmatch 不是 nullptr ，它還把匹配結果寫入 QRegularExpressionMatch 對象指嚮的 rmatch .

範例：

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

該函數在 Qt 5.5 引入。

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

插入字符串 str at the given index position 並返迴此字符串的引用。

範例：

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

若給定 position 大於 size (), the array is first extended using resize ().

另請參閱 append (), prepend (), replace ()，和 remove ().

QString &QString:: insert ( int position , QChar ch )

This function overloads insert().

插入 ch at the given index position 在字符串中。

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

This function overloads insert().

Inserts the first size characters of the QChar array unicode at the given index position 在字符串中。

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

This function overloads insert().

Inserts the string reference str at the given index position 並返迴此字符串的引用。

若給定 position 大於 size (), the array is first extended using resize ().

該函數在 Qt 5.5 引入。

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

This function overloads insert().

Inserts the string reference str at the given index position 並返迴此字符串的引用。

若給定 position 大於 size (), the array is first extended using resize ().

注意： This method has been added in 5.15.2 to simplify writing code that is portable between Qt 5.15 and Qt 6.

This function was introduced in Qt 5.15.2.

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

This function overloads insert().

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

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

This function overloads insert().

Inserts the C string str at the given index position 並返迴此字符串的引用。

若給定 position 大於 size (), the array is first extended using resize ().

This function is not available when QT_NO_CAST_FROM_ASCII 有定義。

該函數在 Qt 5.5 引入。

另請參閱 QT_NO_CAST_FROM_ASCII .

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

This function overloads insert().

Inserts the byte array str at the given index position 並返迴此字符串的引用。

若給定 position 大於 size (), the array is first extended using resize ().

This function is not available when QT_NO_CAST_FROM_ASCII 有定義。

該函數在 Qt 5.5 引入。

另請參閱 QT_NO_CAST_FROM_ASCII .

bool QString:: isEmpty () const

返迴 true if the string has no characters; otherwise returns false .

範例：

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

另請參閱 size ().

bool QString:: isLower () const

返迴 true if the string is lowercase, that is, it's identical to its toLower () folding.

Note that this does not mean that the string does not contain uppercase letters (some uppercase letters do not have a lowercase folding; they are left unchanged by toLower ()). For more information, refer to the Unicode standard, section 3.13.

該函數在 Qt 5.12 引入。

另請參閱 QChar::toLower () 和 isUpper ().

bool QString:: isNull () const

返迴 true if this string is null; otherwise returns false .

範例：

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 () 函數。

另請參閱 isEmpty ().

bool QString:: isRightToLeft () const

返迴 true if the string is read right to left.

另請參閱 QStringRef::isRightToLeft ().

bool QString:: isUpper () const

返迴 true if the string is uppercase, that is, it's identical to its toUpper () folding.

Note that this does not mean that the string does not contain lowercase letters (some lowercase letters do not have a uppercase folding; they are left unchanged by toUpper ()). For more information, refer to the Unicode standard, section 3.13.

該函數在 Qt 5.12 引入。

另請參閱 QChar::toUpper () 和 isLower ().

bool QString:: isValidUtf16 () const

返迴 true if the string contains valid UTF-16 encoded data, or false 否則。

Note that this function does not perform any special validation of the data; it merely checks if it can be successfully decoded from UTF-16. The data is assumed to be in host byte order; the presence of a BOM is meaningless.

該函數在 Qt 5.15 引入。

另請參閱 QStringView::isValidUtf16 ().

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。

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

範例：

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
					

另請參閱 indexOf (), contains ()，和 count ().

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

This function overloads lastIndexOf().

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

This function overloads lastIndexOf().

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。

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

範例：

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
					

該函數在 Qt 4.5 引入。

另請參閱 indexOf (), contains ()，和 count ().

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

This function overloads lastIndexOf().

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。

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

該函數在 Qt 4.8 引入。

另請參閱 indexOf (), contains ()，和 count ().

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

This function overloads lastIndexOf().

Returns the index position of the last occurrence of the string view 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。

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

該函數在 Qt 5.14 引入。

另請參閱 indexOf (), contains ()，和 count ().

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

This function overloads lastIndexOf().

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.

範例：

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

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

This function overloads lastIndexOf().

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 ).

範例：

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

該函數在 Qt 4.5 引入。

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

This function overloads lastIndexOf().

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.

範例：

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

該函數在 Qt 5.0 引入。

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

這是重載函數。

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.

若匹配成功且 rmatch 不是 nullptr ，它還把匹配結果寫入 QRegularExpressionMatch 對象指嚮的 rmatch .

範例：

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

注意： Due to how the regular expression matching algorithm works, this function will actually match repeatedly from the beginning of the string until the position from is reached.

該函數在 Qt 5.5 引入。

QString QString:: left ( int n ) const

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

返迴整個字符串若 n >= size ()，或小於 0。

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

另請參閱 right (), mid (), startsWith (), chopped (), chop ()，和 truncate ().

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.

若 truncate is false 和 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..."
					

若 truncate is true 和 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"
					

另請參閱 rightJustified ().

QStringRef QString:: leftRef ( int n ) const

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

若 n >= size (), or less than zero, a reference to the entire string is returned.

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

該函數在 Qt 4.4 引入。

另請參閱 left (), rightRef (), midRef ()，和 startsWith ().

int QString:: length () const

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

另請參閱 resize ().

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

比較 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.

另請參閱 compare (), QLocale ，和 Comparing Strings .

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

This function overloads localeAwareCompare().

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 字符串。

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

如同 localeAwareCompare(*this, other) .

另請參閱 Comparing Strings .

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

This function overloads localeAwareCompare().

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 字符串。

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

如同 localeAwareCompare(*this, other) .

該函數在 Qt 4.5 引入。

另請參閱 Comparing Strings .

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

This function overloads localeAwareCompare().

比較 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.

該函數在 Qt 4.5 引入。

另請參閱 Comparing Strings .

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

返迴字符串包含 n 個字符對於此字符串，起始於指定 position 索引。

返迴 null 字符串若 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 .

範例：

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

另請參閱 left (), right (), chopped (), chop ()，和 truncate ().

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

Returns a substring reference to n 個字符對於此字符串，起始於指定 position .

若 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.

範例：

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

該函數在 Qt 4.4 引入。

另請參閱 mid (), leftRef ()，和 rightRef ().

QString QString:: normalized ( QString::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 根據指定 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.

格式始終使用 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"
					

另請參閱 setNum ().

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

這是重載函數。

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

這是重載函數。

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

這是重載函數。

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

這是重載函數。

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

這是重載函數。

[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 。見 自變量格式 瞭解細節。

不像 QLocale::toString (), this function does not honor the user's locale settings.

另請參閱 setNum () 和 QLocale::toString ().

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

前置字符串 str to the beginning of this string and returns a reference to this string.

範例：

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

另請參閱 append () 和 insert ().

QString &QString:: prepend ( QChar ch )

This function overloads prepend().

前置字符 ch 到此字符串。

QString &QString:: prepend (const QChar * str , int len )

This function overloads prepend().

前置 len 字符來自 QChar array str to this string and returns a reference to this string.

該函數在 Qt 5.5 引入。

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

This function overloads prepend().

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

該函數在 Qt 5.5 引入。

QString &QString:: prepend ( QLatin1String str )

This function overloads prepend().

Prepends the Latin-1 string str 到此字符串。

QString &QString:: prepend ( QStringView str )

Prepends the given string str to this string and returns the result.

注意： This method has been added in 5.15.2 to simplify writing code that is portable between Qt 5.15 and Qt 6.

This function was introduced in Qt 5.15.2.

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

This function overloads prepend().

前置字符串 str to this string. The const char pointer is converted to Unicode using the fromUtf8 () 函數。

可以禁用此函數通過定義 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.

另請參閱 QT_NO_CAST_FROM_ASCII .

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

This function overloads prepend().

前置字節數組 ba to this string. The byte array is converted to Unicode using the fromUtf8 () 函數。

可以禁用此函數通過定義 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.

另請參閱 QT_NO_CAST_FROM_ASCII .

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) .

另請參閱 append ().

void QString:: push_back ( QChar ch )

這是重載函數。

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) .

另請參閱 prepend ().

void QString:: push_front ( QChar ch )

這是重載函數。

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

QString::reverse_iterator QString:: rbegin ()

返迴 STL-style reverse iterator pointing to the first character in the string, in reverse order.

該函數在 Qt 5.6 引入。

另請參閱 begin (), crbegin ()，和 rend ().

QString::const_reverse_iterator QString:: rbegin () const

這是重載函數。

該函數在 Qt 5.6 引入。

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

移除 n characters from the string, starting at the given position index, and returns a reference to the string.

若指定 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"
					

另請參閱 insert () 和 replace ().

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.

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

範例：

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

這如同 replace(ch, "", cs) .

另請參閱 replace ().

QString &QString:: remove ( QLatin1String str , Qt::CaseSensitivity cs = Qt::CaseSensitive)

這是重載函數。

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

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

這如同 replace(str, "", cs) .

該函數在 Qt 5.11 引入。

另請參閱 replace ().

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.

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

這如同 replace(str, "", cs) .

另請參閱 replace ().

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"
					

另請參閱 indexOf (), lastIndexOf ()，和 replace ().

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"
					

該函數在 Qt 5.0 引入。

另請參閱 indexOf (), lastIndexOf ()，和 replace ().

QString::reverse_iterator QString:: rend ()

返迴 STL-style reverse iterator pointing to one past the last character in the string, in reverse order.

該函數在 Qt 5.6 引入。

另請參閱 end (), crend ()，和 rbegin ().

QString::const_reverse_iterator QString:: rend () const

這是重載函數。

該函數在 Qt 5.6 引入。

QString QString:: repeated ( int times ) const

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

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

範例：

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

該函數在 Qt 4.5 引入。

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

替換 n characters beginning at index position 采用字符串 after 並返迴此字符串的引用。

注意： 若指定 position index is within the string, but position + n goes outside the strings range, then n will be adjusted to stop at the end of the string.

範例：

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

另請參閱 insert () 和 remove ().

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

此函數重載 replace()。

替換 n characters beginning at index position with the character after 並返迴此字符串的引用。

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

此函數重載 replace()。

替換 n characters beginning at index position with the first size characters of the QChar array unicode 並返迴此字符串的引用。

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

此函數重載 replace()。

Replaces every occurrence of the character before with the character after 並返迴此字符串的引用。

若 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)

此函數重載 replace()。

Replaces each occurrence in this string of the first blen 字符的 before with the first alen 字符的 after 並返迴此字符串的引用。

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

該函數在 Qt 4.5 引入。

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

此函數重載 replace()。

Replaces every occurrence of the string before 采用字符串 after 並返迴此字符串的引用。

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

注意： The text is not rescanned after a replacement.

該函數在 Qt 4.5 引入。

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

此函數重載 replace()。

Replaces every occurrence of the string before 采用字符串 after 並返迴此字符串的引用。

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

注意： The text is not rescanned after a replacement.

該函數在 Qt 4.5 引入。

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

此函數重載 replace()。

Replaces every occurrence of the string before 采用字符串 after 並返迴此字符串的引用。

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

注意： The text is not rescanned after a replacement.

該函數在 Qt 4.5 引入。

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

此函數重載 replace()。

Replaces every occurrence of the string before 采用字符串 after 並返迴此字符串的引用。

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

範例：

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

注意： The replacement text is not rescanned after it is inserted.

範例：

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

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

此函數重載 replace()。

Replaces every occurrence of the character ch in the string with after 並返迴此字符串的引用。

若 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)

此函數重載 replace()。

Replaces every occurrence of the character c 采用字符串 after 並返迴此字符串的引用。

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

注意： The text is not rescanned after a replacement.

該函數在 Qt 4.5 引入。

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

此函數重載 replace()。

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}."
					

另請參閱 indexOf (), lastIndexOf (), remove ()，和 QRegExp::cap ().

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

此函數重載 replace()。

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}."
					

該函數在 Qt 5.0 引入。

另請參閱 indexOf (), lastIndexOf (), remove (), QRegularExpression ，和 QRegularExpressionMatch .

void QString:: reserve ( int size )

試圖分配內存為至少 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();
					

另請參閱 squeeze () 和 capacity ().

void QString:: resize ( int size )

Sets the size of the string to size 字符。

若 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.

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

範例：

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 () 函數：

若 size 為負，相當於傳遞 0。

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

另請參閱 truncate () 和 reserve ().

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

這是重載函數。

不像 resize (int), this overload initializes the new characters to fillChar :

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

該函數在 Qt 5.7 引入。

QString QString:: right ( int n ) const

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

返迴整個字符串若 n >= size ()，或小於 0。

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

另請參閱 left (), mid (), endsWith (), chopped (), chop ()，和 truncate ().

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

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

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

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

若 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"
					

另請參閱 leftJustified ().

QStringRef QString:: rightRef ( int n ) const

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

若 n >= size (), or less than zero, a reference to the entire string is returned.

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

該函數在 Qt 4.4 引入。

另請參閱 right (), leftRef (), midRef ()，和 endsWith ().