The QByteArray 類提供字節數組。 更多...
| 頭： | #include <QByteArray> |
| qmake: | QT += core |
注意： 此類的所有函數 可重入 .
| enum | Base64Option { Base64Encoding, Base64UrlEncoding, KeepTrailingEquals, OmitTrailingEquals } |
| flags | Base64Options |
| typedef | const_iterator |
| typedef | const_reverse_iterator |
| typedef | iterator |
| typedef | reverse_iterator |
| QByteArray () | |
| QByteArray (const char * data , int size = -1) | |
| QByteArray (int size , char ch ) | |
| QByteArray (const QByteArray & other ) | |
| QByteArray (QByteArray && other ) | |
| ~QByteArray () | |
| QByteArray & | append (const QByteArray & ba ) |
| QByteArray & | append (int count , char ch ) |
| QByteArray & | append (const char * str ) |
| QByteArray & | append (const char * str , int len ) |
| QByteArray & | append (char ch ) |
| QByteArray & | append (const QString & str ) |
| char | at (int i ) const |
| char | back () const |
| QByteRef | back () |
| QByteArray::iterator | begin () |
| QByteArray::const_iterator | begin () const |
| int | capacity () const |
| QByteArray::const_iterator | cbegin () const |
| QByteArray::const_iterator | cend () const |
| void | chop (int n ) |
| QByteArray | chopped (int len ) const |
| void | clear () |
| int | compare (const char * c , Qt::CaseSensitivity cs = ...) const |
| int | compare (const QByteArray & a , Qt::CaseSensitivity cs = ...) const |
| QByteArray::const_iterator | constBegin () const |
| const char * | constData () const |
| QByteArray::const_iterator | constEnd () const |
| bool | contains (const QByteArray & ba ) const |
| bool | contains (const char * str ) const |
| bool | contains (char ch ) const |
| int | count (const QByteArray & ba ) const |
| int | count (const char * str ) const |
| int | count (char ch ) const |
| int | count () const |
| QByteArray::const_reverse_iterator | crbegin () const |
| QByteArray::const_reverse_iterator | crend () const |
| char * | data () |
| const char * | data () const |
| QByteArray::iterator | end () |
| QByteArray::const_iterator | end () const |
| bool | endsWith (const QByteArray & ba ) const |
| bool | endsWith (char ch ) const |
| bool | endsWith (const char * str ) const |
| QByteArray & | fill (char ch , int size = -1) |
| char | front () const |
| QByteRef | front () |
| int | indexOf (const QByteArray & ba , int from = 0) const |
| int | indexOf (const char * str , int from = 0) const |
| int | indexOf (char ch , int from = 0) const |
| int | indexOf (const QString & str , int from = 0) const |
| QByteArray & | insert (int i , const QByteArray & ba ) |
| QByteArray & | insert (int i , int count , char ch ) |
| QByteArray & | insert (int i , const char * str ) |
| QByteArray & | insert (int i , const char * str , int len ) |
| QByteArray & | insert (int i , char ch ) |
| QByteArray & | insert (int i , const QString & str ) |
| bool | isEmpty () const |
| bool | isLower () const |
| bool | isNull () const |
| bool | isUpper () const |
| int | lastIndexOf (const QByteArray & ba , int from = -1) const |
| int | lastIndexOf (const char * str , int from = -1) const |
| int | lastIndexOf (char ch , int from = -1) const |
| int | lastIndexOf (const QString & str , int from = -1) const |
| QByteArray | left (int len ) const |
| QByteArray | leftJustified (int width , char fill = ' ', bool truncate = false) const |
| int | length () const |
| QByteArray | mid (int pos , int len = -1) const |
| QByteArray & | prepend (const QByteArray & ba ) |
| QByteArray & | prepend (int count , char ch ) |
| QByteArray & | prepend (const char * str ) |
| QByteArray & | prepend (const char * str , int len ) |
| QByteArray & | prepend (char ch ) |
| void | push_back (const QByteArray & other ) |
| void | push_back (const char * str ) |
| void | push_back (char ch ) |
| void | push_front (const QByteArray & other ) |
| void | push_front (const char * str ) |
| void | push_front (char ch ) |
| QByteArray::reverse_iterator | rbegin () |
| QByteArray::const_reverse_iterator | rbegin () const |
| QByteArray & | remove (int pos , int len ) |
| QByteArray::reverse_iterator | rend () |
| QByteArray::const_reverse_iterator | rend () const |
| QByteArray | repeated (int times ) const |
| QByteArray & | replace (int pos , int len , const QByteArray & after ) |
| QByteArray & | replace (int pos , int len , const char * after , int alen ) |
| QByteArray & | replace (int pos , int len , const char * after ) |
| QByteArray & | replace (char before , const char * after ) |
| QByteArray & | replace (char before , const QByteArray & after ) |
| QByteArray & | replace (const char * before , const char * after ) |
| QByteArray & | replace (const char * before , int bsize , const char * after , int asize ) |
| QByteArray & | replace (const QByteArray & before , const QByteArray & after ) |
| QByteArray & | replace (const QByteArray & before , const char * after ) |
| QByteArray & | replace (const char * before , const QByteArray & after ) |
| QByteArray & | replace (char before , char after ) |
| QByteArray & | replace (const QString & before , const char * after ) |
| QByteArray & | replace (char before , const QString & after ) |
| QByteArray & | replace (const QString & before , const QByteArray & after ) |
| void | reserve (int size ) |
| void | resize (int size ) |
| QByteArray | right (int len ) const |
| QByteArray | rightJustified (int width , char fill = ' ', bool truncate = false) const |
| QByteArray & | setNum (int n , int base = 10) |
| QByteArray & | setNum (ushort n , int base = 10) |
| QByteArray & | setNum (short n , int base = 10) |
| QByteArray & | setNum (uint n , int base = 10) |
| QByteArray & | setNum (qlonglong n , int base = 10) |
| QByteArray & | setNum (qulonglong n , int base = 10) |
| QByteArray & | setNum (float n , char f = 'g', int prec = 6) |
| QByteArray & | setNum (double n , char f = 'g', int prec = 6) |
| QByteArray & | setRawData (const char * data , uint size ) |
| void | shrink_to_fit () |
| QByteArray | simplified () const |
| int | size () const |
| QList<QByteArray> | split (char sep ) const |
| void | squeeze () |
| bool | startsWith (const QByteArray & ba ) const |
| bool | startsWith (char ch ) const |
| bool | startsWith (const char * str ) const |
| void | swap (QByteArray & other ) |
| QByteArray | toBase64 () const |
| QByteArray | toBase64 (QByteArray::Base64Options options ) const |
| CFDataRef | toCFData () const |
| double | toDouble (bool * ok = nullptr) const |
| float | toFloat (bool * ok = nullptr) const |
| QByteArray | toHex () const |
| QByteArray | toHex (char separator ) const |
| int | toInt (bool * ok = nullptr, int base = 10) const |
| long | toLong (bool * ok = nullptr, int base = 10) const |
| qlonglong | toLongLong (bool * ok = nullptr, int base = 10) const |
| QByteArray | toLower () const |
| NSData * | toNSData () const |
| QByteArray | toPercentEncoding (const QByteArray & exclude = QByteArray(), const QByteArray & 包括 = QByteArray(), char percent = '%') const |
| CFDataRef | toRawCFData () const |
| NSData * | toRawNSData () const |
| short | toShort (bool * ok = nullptr, int base = 10) const |
| std::string | toStdString () const |
| uint | toUInt (bool * ok = nullptr, int base = 10) const |
| ulong | toULong (bool * ok = nullptr, int base = 10) const |
| qulonglong | toULongLong (bool * ok = nullptr, int base = 10) const |
| ushort | toUShort (bool * ok = nullptr, int base = 10) const |
| QByteArray | toUpper () const |
| QByteArray | trimmed () const |
| void | truncate (int pos ) |
| const char * | operator const char * () const |
| const void * | operator const void * () const |
| bool | operator!= (const QString & str ) const |
| QByteArray & | operator+= (const QByteArray & ba ) |
| QByteArray & | operator+= (const char * str ) |
| QByteArray & | operator+= (char ch ) |
| QByteArray & | operator+= (const QString & str ) |
| bool | operator< (const QString & str ) const |
| bool | operator<= (const QString & str ) const |
| QByteArray & | operator= (const QByteArray & other ) |
| QByteArray & | operator= (const char * str ) |
| QByteArray & | operator= (QByteArray && other ) |
| bool | operator== (const QString & str ) const |
| bool | operator> (const QString & str ) const |
| bool | operator>= (const QString & str ) const |
| QByteRef | operator[] (int i ) |
| char | operator[] (uint i ) const |
| char | operator[] (int i ) const |
| QByteRef | operator[] (uint i ) |
| QByteArray | fromBase64 (const QByteArray & base64 ) |
| QByteArray | fromBase64 (const QByteArray & base64 , QByteArray::Base64Options options ) |
| QByteArray | fromCFData (CFDataRef data ) |
| QByteArray | fromHex (const QByteArray & hexEncoded ) |
| QByteArray | fromNSData (const NSData * data ) |
| QByteArray | fromPercentEncoding (const QByteArray & input , char percent = '%') |
| QByteArray | fromRawCFData (CFDataRef data ) |
| QByteArray | fromRawData (const char * data , int size ) |
| QByteArray | fromRawNSData (const NSData * data ) |
| QByteArray | fromStdString (const std::string & str ) |
| QByteArray | number (int n , int base = 10) |
| QByteArray | number (uint n , int base = 10) |
| QByteArray | number (qlonglong n , int base = 10) |
| QByteArray | number (qulonglong n , int base = 10) |
| QByteArray | number (double n , char f = 'g', int prec = 6) |
| quint16 | qChecksum (const char * data , uint len ) |
| quint16 | qChecksum (const char * data , uint len , Qt::ChecksumType standard ) |
| QByteArray | qCompress (const uchar * data , int nbytes , int compressionLevel = -1) |
| QByteArray | qCompress (const QByteArray & data , int compressionLevel = -1) |
| QByteArray | qUncompress (const uchar * data , int nbytes ) |
| QByteArray | qUncompress (const QByteArray & data ) |
| int | qsnprintf (char * str , size_t n , const char * fmt , ... ) |
| int | qstrcmp (const char * str1 , const char * str2 ) |
| char * | qstrcpy (char * dst , const char * src ) |
| char * | qstrdup (const char * src ) |
| int | qstricmp (const char * str1 , const char * str2 ) |
| uint | qstrlen (const char * str ) |
| int | qstrncmp (const char * str1 , const char * str2 , uint len ) |
| char * | qstrncpy (char * dst , const char * src , uint len ) |
| int | qstrnicmp (const char * str1 , const char * str2 , uint len ) |
| uint | qstrnlen (const char * str , uint maxlen ) |
| int | qvsnprintf (char * str , size_t n , const char * fmt , va_list ap ) |
| bool | operator!= (const QByteArray & a1 , const QByteArray & a2 ) |
| bool | operator!= (const QByteArray & a1 , const char * a2 ) |
| bool | operator!= (const char * a1 , const QByteArray & a2 ) |
| const QByteArray | operator+ (const QByteArray & a1 , const QByteArray & a2 ) |
| const QByteArray | operator+ (const QByteArray & a1 , const char * a2 ) |
| const QByteArray | operator+ (const QByteArray & a1 , char a2 ) |
| const QByteArray | operator+ (const char * a1 , const QByteArray & a2 ) |
| const QByteArray | operator+ (char a1 , const QByteArray & a2 ) |
| bool | operator< (const QByteArray & a1 , const QByteArray & a2 ) |
| bool | operator< (const QByteArray & a1 , const char * a2 ) |
| bool | operator< (const char * a1 , const QByteArray & a2 ) |
| QDataStream & | operator<< (QDataStream & out , const QByteArray & ba ) |
| bool | operator<= (const QByteArray & a1 , const QByteArray & a2 ) |
| bool | operator<= (const QByteArray & a1 , const char * a2 ) |
| bool | operator<= (const char * a1 , const QByteArray & a2 ) |
| bool | operator== (const QByteArray & a1 , const QByteArray & a2 ) |
| bool | operator== (const QByteArray & a1 , const char * a2 ) |
| bool | operator== (const char * a1 , const QByteArray & a2 ) |
| bool | operator> (const QByteArray & a1 , const QByteArray & a2 ) |
| bool | operator> (const QByteArray & a1 , const char * a2 ) |
| bool | operator> (const char * a1 , const QByteArray & a2 ) |
| bool | operator>= (const QByteArray & a1 , const QByteArray & a2 ) |
| bool | operator>= (const QByteArray & a1 , const char * a2 ) |
| bool | operator>= (const char * a1 , const QByteArray & a2 ) |
| QDataStream & | operator>> (QDataStream & in , QByteArray & ba ) |
| QByteArrayLiteral ( ba ) | |
| QT_NO_CAST_FROM_BYTEARRAY |
The QByteArray 類提供字節數組。
QByteArray
可以用於存儲原生字節 (包括 \0) 和傳統 8 位以 \0 結尾的字符串。使用
QByteArray
更方便比使用
const char *
。在幕後，它始終確保數據之後緊跟 \0 終止符，並使用
隱式共享
(寫入時拷貝) 以縮減內存用量並避免不必要的數據拷貝。
除瞭 QByteArray ，Qt 還提供 QString 類以存儲字符串數據。對於大多數目的， QString 是您想要使用的類。它存儲 16 位 Unicode 字符，使之能在應用程序中輕鬆存儲非 ASCII 和非 Latin-1 字符。此外， QString 在 Qt API 中貫穿始終。這 2 種主要情況 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 (如：采用 Qt for Embedded Linux)。
一種方式初始化
QByteArray
是隻需傳遞
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 的字節數組：
QByteArray ba("Hello");
盡管 size () is 5, the byte array also maintains an extra '\0' character at the end so that if a function is used that asks for a pointer to the underlying data (e.g. a call to data ()), the data pointed to is guaranteed to be '\0'-terminated.
QByteArray
makes a deep copy of the
const char *
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
QByteArray::fromRawData
() instead.)
Another approach is to set the size of the array using resize () and to initialize the data byte per byte. QByteArray uses 0-based indexes, just like C++ arrays. To access the byte at a particular index position, you can use operator[](). On non-const byte arrays, operator[]() returns a reference to a byte that can be used on the left side of an assignment. For example:
QByteArray ba; ba.resize(5); ba[0] = 0x3c; ba[1] = 0xb8; ba[2] = 0x64; ba[3] = 0x18; ba[4] = 0xca;
For read-only access, an alternative syntax is to use at ():
for (int i = 0; i < ba.size(); ++i) { if (ba.at(i) >= 'a' && ba.at(i) <= 'f') cout << "Found character in range [a-f]" << endl; }
at () can be faster than operator[](), because it never causes a 深拷貝 的齣現。
要每次提取多個字節，使用 left (), right ()，或 mid ().
A QByteArray 可以嵌入 \0 字節。 size () function always returns the size of the whole array, including embedded '\0' bytes, but excluding the terminating '\0' added by QByteArray 。例如：
QByteArray ba1("ca\0r\0t"); ba1.size(); // Returns 2. ba1.constData(); // Returns "ca" with terminating \0. QByteArray ba2("ca\0r\0t", 3); ba2.size(); // Returns 3. ba2.constData(); // Returns "ca\0" with terminating \0. QByteArray ba3("ca\0r\0t", 4); ba3.size(); // Returns 4. ba3.constData(); // Returns "ca\0r" with terminating \0. const char cart[] = {'c', 'a', '\0', 'r', '\0', 't'}; QByteArray ba4(QByteArray::fromRawData(cart, 6)); ba4.size(); // Returns 6. ba4.constData(); // Returns "ca\0r\0t" without terminating \0.
If you want to obtain the length of the data up to and excluding the first '\0' character, call qstrlen () on the byte array.
After a call to resize (), newly allocated bytes have undefined values. To set all the bytes to a particular value, call fill ().
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 data. The pointer is guaranteed to remain valid until a non-const function is called on the QByteArray . It is also guaranteed that the data ends with a '\0' byte unless the QByteArray was created from a raw data . This '\0' byte is automatically provided by QByteArray and is not counted in size ().
QByteArray provides the following basic functions for modifying the byte data: append (), prepend (), insert (), replace ()，和 remove ()。例如：
QByteArray x("and"); x.prepend("rock "); // x == "rock and" x.append(" roll"); // x == "rock and roll" x.replace(5, 3, "&"); // x == "rock & roll"
The replace () 和 remove () functions' first two arguments are the position from which to start erasing and the number of bytes that should be erased.
When you append () data to a non-empty array, the array will be reallocated and the new data copied to it. You can avoid this behavior by calling reserve (), which preallocates a certain amount of memory. You can also call capacity () to find out how much memory QByteArray actually allocated. Data appended to an empty array is not copied.
A frequent requirement is to remove whitespace characters from a byte array ('\n', '\t', ' ', etc.). If you want to remove whitespace from both ends of a QByteArray ，使用 trimmed (). If you want to remove whitespace from both ends and replace multiple consecutive whitespaces with a single space character within the byte array, use simplified ().
If you want to find all occurrences of a particular character or substring in a QByteArray ，使用 indexOf () 或 lastIndexOf (). 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:
QByteArray ba("We must be <b>bold</b>, very <b>bold</b>"); int j = 0; while ((j = ba.indexOf("<b>", j)) != -1) { cout << "Found <b> tag at index position " << j << endl; ++j; }
If you simply want to check whether a QByteArray contains a particular character or substring, use contains (). If you want to find out how many times a particular character or substring occurs in the byte array, use count (). If you want to replace all occurrences of a particular value with another, use one of the two-parameter replace () overloads.
QByteArray s can be compared using overloaded operators such as operator<(), operator<=(), operator==(), operator>=(), and so on. The comparison is based exclusively on the numeric values of the characters and is very fast, but is not what a human would expect. QString::localeAwareCompare () is a better choice for sorting user-interface strings.
For historical reasons, QByteArray distinguishes between a null byte array and an empty byte array. A null byte array is a byte array that is initialized using QByteArray 's default constructor or by passing (const char *)0 to the constructor. An empty byte array is any byte array with size 0. A null byte array is always empty, but an empty byte array isn't necessarily null:
QByteArray().isNull(); // returns true QByteArray().isEmpty(); // returns true QByteArray("").isNull(); // returns false QByteArray("").isEmpty(); // returns true QByteArray("abc").isNull(); // returns false QByteArray("abc").isEmpty(); // returns false
所有函數除瞭 isNull () treat null byte arrays the same as empty byte arrays. For example, data () returns a pointer to a '\0' character for a null byte array ( not a null pointer), and QByteArray () compares equal to QByteArray (""). We recommend that you always use isEmpty () and avoid isNull ().
Functions that perform conversions between numeric data types and strings are performed in the C locale, irrespective of the user's locale settings. Use QString to perform locale-aware conversions between numbers and strings.
在
QByteArray
, the notion of uppercase and lowercase and of which character is greater than or less than another character is locale dependent. This affects functions that support a case insensitive option or that compare or lowercase or uppercase their arguments. Case insensitive operations and comparisons will be accurate if both strings contain only ASCII characters. (If
$LC_CTYPE
is set, most Unix systems do "the right thing".) Functions that this affects include
contains
(),
indexOf
(),
lastIndexOf
(), operator<(), operator<=(), operator>(), operator>=(),
isLower
(),
isUpper
(),
toLower
() 和
toUpper
().
This issue does not apply to QString s since they represent characters using Unicode.
This enum contains the options available for encoding and decoding Base64. Base64 is defined by RFC 4648 , with the following options:
| 常量 | 值 | 描述 |
|---|---|---|
QByteArray::Base64Encoding
|
0
|
(default) The regular Base64 alphabet, called simply "base64" |
QByteArray::Base64UrlEncoding
|
1
|
An alternate alphabet, called "base64url", which replaces two characters in the alphabet to be more friendly to URLs. |
QByteArray::KeepTrailingEquals
|
0
|
(default) Keeps the trailing padding equal signs at the end of the encoded data, so the data is always a size multiple of four. |
QByteArray::OmitTrailingEquals
|
2
|
Omits adding the padding equal signs at the end of the encoded data. |
QByteArray::fromBase64 () ignores the KeepTrailingEquals and OmitTrailingEquals options and will not flag errors in case they are missing or if there are too many of them.
該枚舉在 Qt 5.2 引入或被修改。
The Base64Options type is a typedef for QFlags <Base64Option>. It stores an OR combination of Base64Option values.
此 typedef 提供 STL 樣式 const 迭代器為 QByteArray .
另請參閱 QByteArray::const_reverse_iterator and QByteArray::iterator .
This typedef provides an STL-style const reverse iterator for QByteArray .
該 typedef 在 Qt 5.6 引入。
另請參閱 QByteArray::reverse_iterator and QByteArray::const_iterator .
This typedef provides an STL-style non-const iterator for QByteArray .
另請參閱 QByteArray::reverse_iterator and QByteArray::const_iterator .
This typedef provides an STL-style non-const reverse iterator for QByteArray .
該 typedef 在 Qt 5.6 引入。
另請參閱 QByteArray::const_reverse_iterator and QByteArray::iterator .
構造空字節數組。
另請參閱 isEmpty ().
構造字節數組包含前 size 字節的數組 data .
若 data 為 0，構造 null 字節數組。
若 size 為負， data is assumed to point to a nul-terminated string and its length is determined dynamically. The terminating nul-character is not considered part of the byte array.
QByteArray 製作字符串數據的深拷貝。
另請參閱 fromRawData ().
構造字節數組大小為 size 采用將每字節設為字符 ch .
另請參閱 fill ().
構造副本為 other .
此操作花費 常量時間 ，因為 QByteArray is 隱式共享 . This makes returning a QByteArray from a function very fast. If a shared instance is modified, it will be copied (copy-on-write), taking 綫性時間 .
另請參閱 operator= ().
移動構造 QByteArray 實例，使之指嚮同一對象如 other 所指嚮的。
該函數在 Qt 5.2 引入。
銷毀字節數組。
追加字節數組 ba 到此字節數組的末尾。
範例：
QByteArray x("free"); QByteArray y("dom"); x.append(y); // x == "freedom"
這如同 insert( size (), ba ).
注意： QByteArray 是 隱式共享 類。因此，若追加到空字節數組，那麼字節數組將僅僅共享的數據保持在 ba 。在這種情況下，不進行數據拷貝，花費 常量時間 。若共享實例被修改，它將被拷貝 (寫時拷貝)，花費 綫性時間 .
若要追加到的字節數組非空，履行數據深拷貝，花費 綫性時間 .
This operation typically does not suffer from allocation overhead, because QByteArray preallocates extra space at the end of the data so that it may grow without reallocating for each append operation.
另請參閱 operator+= (), prepend ()，和 insert ().
這是重載函數。
追加 count copies of character ch 到此字節數組，並返迴此字節數組的引用。
若 count 為負 (或 0)，什麼都不會追加到字節數組。
該函數在 Qt 5.7 引入。
這是重載函數。
追加字符串 str 到此字節數組。
此函數重載 append ().
追加第一 len characters of the string str 到此字節數組，並返迴此字節數組的引用。
若 len is negative, the length of the string will be determined automatically using qstrlen ()。若 len 為 0 或 str is null, nothing is appended to the byte array. Ensure that len is not longer than str .
這是重載函數。
追加字符 ch 到此字節數組。
這是重載函數。
追加字符串 str to this byte array. The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
可以禁用此函數通過定義
QT_NO_CAST_TO_ASCII
當編譯應用程序時。那麼需要調用
QString::toUtf8
() (或
QString::toLatin1
() 或
QString::toLocal8Bit
()) explicitly if you want to convert the data to
const char *
.
返迴字符在索引位置 i 在字節數組中。
i 必須是字節數組中的有效索引位置 (即 0 <= i < size ()).
另請參閱 operator[] ().
Returns the last character in the byte array. Same as
at(size() - 1)
.
此函數為兼容 STL (標準模闆庫) 提供。
警告： 空字節數組調用此函數，會構成未定義行為。
該函數在 Qt 5.10 引入。
另請參閱 front (), at ()，和 operator[] ().
Returns a reference to the last character in the byte array. Same as
operator[](size() - 1)
.
此函數為兼容 STL (標準模闆庫) 提供。
警告： 空字節數組調用此函數，會構成未定義行為。
該函數在 Qt 5.10 引入。
另請參閱 front (), at ()，和 operator[] ().
返迴 STL 樣式迭代器 pointing to the first character in the byte-array.
另請參閱 constBegin () 和 end ().
此函數重載 begin ().
Returns the maximum number of bytes that can be stored in the byte array without forcing a reallocation.
The sole purpose of this function is to provide a means of fine tuning QByteArray 's memory usage. In general, you will rarely ever need to call this function. If you want to know how many bytes are in the byte array, call size ().
返迴常量 STL 樣式迭代器 pointing to the first character in the byte-array.
該函數在 Qt 5.0 引入。
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。
移除 n bytes from the end of the byte array.
若 n 大於 size (), the result is an empty byte array.
範例：
QByteArray ba("STARTTLS\r\n"); ba.chop(2); // ba == "STARTTLS"
另請參閱 truncate (), resize ()，和 left ().
返迴的字節數組包含最左 size () - len 字節對於此字節數組。
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 ().
Clears the contents of the byte array and makes it null.
Returns an integer less than, equal to, or greater than zero depending on whether this QByteArray sorts before, at the same position, or after the string pointed to by c . The comparison is performed according to case sensitivity cs .
該函數在 Qt 5.12 引入。
另請參閱 operator== .
這是重載函數。
Returns an integer less than, equal to, or greater than zero depending on whether this QByteArray sorts before, at the same position, or after the QByteArray a . The comparison is performed according to case sensitivity cs .
該函數在 Qt 5.12 引入。
另請參閱 operator== .
返迴常量 STL 樣式迭代器 pointing to the first character in the byte-array.
Returns a pointer to the data stored in the byte array. The pointer can be used to access the bytes that compose the array. The data is '\0'-terminated unless the QByteArray object was created from raw data. The pointer remains valid as long as the byte array isn't reallocated or destroyed.
此函數主要用於將字節數組傳遞給的函數接受
const char *
.
注意：
QByteArray
可以存儲任何字節值 (包括 \0)，但大多數函數需要
char *
自變量，假定數據在遇到首個 \0 時結束。
另請參閱 data (), operator[] ()，和 fromRawData ().
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 ().
返迴
true
if the byte array contains an occurrence of the byte array
ba
；否則返迴
false
.
這是重載函數。
返迴
true
if the byte array contains the string
str
；否則返迴
false
.
這是重載函數。
返迴
true
if the byte array contains the character
ch
；否則返迴
false
.
Returns the number of (potentially overlapping) occurrences of byte array ba in this byte array.
另請參閱 contains () 和 indexOf ().
這是重載函數。
Returns the number of (potentially overlapping) occurrences of string str 在字節數組中。
這是重載函數。
返迴齣現數對於字符 ch 在字節數組中。
另請參閱 contains () 和 indexOf ().
這是重載函數。
如同 size ().
返迴常量 STL-style reverse iterator pointing to the first character in the byte-array, in reverse order.
該函數在 Qt 5.6 引入。
另請參閱 begin (), rbegin ()，和 rend ().
返迴常量 STL-style reverse iterator pointing to one past the last character in the byte-array, in reverse order.
該函數在 Qt 5.6 引入。
另請參閱 end (), rend ()，和 rbegin ().
Returns a pointer to the data stored in the byte array. The pointer can be used to access and modify the bytes that compose the array. The data is '\0'-terminated, i.e. the number of bytes in the returned character string is size () + 1 for the '\0' terminator.
範例：
QByteArray ba("Hello world"); char *data = ba.data(); while (*data) { cout << "[" << *data << "]" << endl; ++data; }
The pointer remains valid as long as the byte array isn't reallocated or destroyed. For read-only access, constData () 更快，因為它從不導緻 深拷貝 的齣現。
此函數主要用於將字節數組傳遞給的函數接受
const char *
.
以下範例製作由 data() 返迴的 char* 副本，但會破壞堆並導緻崩潰，因為它沒有為末尾 \0 分配字節：
QString tmp = "test"; QByteArray text = tmp.toLocal8Bit(); char *data = new char[text.size()]; strcpy(data, text.data()); delete [] data;
這個分配瞭正確的空間數量：
QString tmp = "test"; QByteArray text = tmp.toLocal8Bit(); char *data = new char[text.size() + 1]; strcpy(data, text.data()); delete [] data;
注意：
QByteArray
可以存儲任何字節值 (包括 \0)，但大多數函數需要
char *
自變量，假定數據在遇到首個 \0 時結束。
另請參閱 constData () 和 operator[] ().
這是重載函數。
返迴 STL 樣式迭代器 pointing to the imaginary character after the last character in the byte-array.
此函數重載 end ().
返迴
true
if this byte array ends with byte array
ba
；否則返迴
false
.
範例：
QByteArray url("http://qt-project.org/doc/qt-5.0/qtdoc/index.html"); if (url.endsWith(".html")) ...
另請參閱 startsWith () 和 right ().
這是重載函數。
返迴
true
if this byte array ends with character
ch
；否則返迴
false
.
這是重載函數。
返迴
true
if this byte array ends with string
str
；否則返迴
false
.
Sets every byte in the byte array to character ch 。若 size is different from -1 (the default), the byte array is resized to size size 事先。
範例：
QByteArray ba("Istambul"); ba.fill('o'); // ba == "oooooooo" ba.fill('X', 2); // ba == "XX"
另請參閱 resize ().
[static]
QByteArray
QByteArray::
fromBase64
(const
QByteArray
&
base64
)
Returns a decoded copy of the Base64 array base64 . Input is not checked for validity; invalid characters in the input are skipped, enabling the decoding process to continue with subsequent characters.
例如：
QByteArray text = QByteArray::fromBase64("UXQgaXMgZ3JlYXQh"); text.data(); // returns "Qt is great!"
The algorithm used to decode Base64-encoded data is defined in RFC 4648 .
另請參閱 toBase64 ().
[static]
QByteArray
QByteArray::
fromBase64
(const
QByteArray
&
base64
,
QByteArray::Base64Options
options
)
這是重載函數。
Returns a decoded copy of the Base64 array base64 , using the alphabet defined by options . Input is not checked for validity; invalid characters in the input are skipped, enabling the decoding process to continue with subsequent characters.
例如：
QByteArray::fromBase64("PHA+SGVsbG8/PC9wPg==", QByteArray::Base64Encoding); // returns "<p>Hello?</p>" QByteArray::fromBase64("PHA-SGVsbG8_PC9wPg==", QByteArray::Base64UrlEncoding); // returns "<p>Hello?</p>"
The algorithm used to decode Base64-encoded data is defined in RFC 4648 .
該函數在 Qt 5.2 引入。
另請參閱 toBase64 ().
[static]
QByteArray
QByteArray::
fromCFData
(
CFDataRef
data
)
構造新的 QByteArray containing a copy of the CFData data .
該函數在 Qt 5.3 引入。
另請參閱 fromRawCFData (), fromRawData (), toRawCFData ()，和 toCFData ().
[static]
QByteArray
QByteArray::
fromHex
(const
QByteArray
&
hexEncoded
)
Returns a decoded copy of the hex encoded array hexEncoded . Input is not checked for validity; invalid characters in the input are skipped, enabling the decoding process to continue with subsequent characters.
例如：
QByteArray text = QByteArray::fromHex("517420697320677265617421"); text.data(); // returns "Qt is great!"
另請參閱 toHex ().
[static]
QByteArray
QByteArray::
fromNSData
(const
NSData
*
data
)
構造新的 QByteArray containing a copy of the NSData data .
該函數在 Qt 5.3 引入。
另請參閱 fromRawNSData (), fromRawData (), toNSData ()，和 toRawNSData ().
[static]
QByteArray
QByteArray::
fromPercentEncoding
(const
QByteArray
&
input
,
char
percent
= '%')
Returns a decoded copy of the URI/URL-style percent-encoded input 。 percent parameter allows you to replace the '%' character for another (for instance, '_' or '=').
例如：
QByteArray text = QByteArray::fromPercentEncoding("Qt%20is%20great%33"); text.data(); // returns "Qt is great!"
注意： 給定無效輸入 (譬如：包含 %G5 序列的字符串，不是有效十六進製數字)，輸齣也將無效。例如：%G5 序列可以解碼為 W。
該函數在 Qt 4.4 引入。
另請參閱 toPercentEncoding () 和 QUrl::fromPercentEncoding ().
[static]
QByteArray
QByteArray::
fromRawCFData
(
CFDataRef
data
)
構造 QByteArray that uses the bytes of the CFData data .
The data 的字節不拷貝。
The caller guarantees that the CFData will not be deleted or modified as long as this QByteArray object exists.
該函數在 Qt 5.3 引入。
另請參閱 fromCFData (), fromRawData (), toRawCFData ()，和 toCFData ().
[static]
QByteArray
QByteArray::
fromRawData
(const
char
*
data
,
int
size
)
構造 QByteArray that uses the first size bytes of the data array. The bytes are not copied. The QByteArray will contain the data pointer. The caller guarantees that data will not be deleted or modified as long as this QByteArray and any copies of it exist that have not been modified. In other words, because QByteArray 是 隱式共享 class and the instance returned by this function contains the data pointer, the caller must not delete data or modify it directly as long as the returned QByteArray and any copies exist. However, QByteArray 未擁有所有權對於 data , so the QByteArray destructor will never delete the raw data , even when the last QByteArray referring to data 被銷毀。
A subsequent attempt to modify the contents of the returned QByteArray or any copy made from it will cause it to create a deep copy of the data array before doing the modification. This ensures that the raw data array itself will never be modified by QByteArray .
Here is an example of how to read data using a QDataStream on raw data in memory without copying the raw data into a QByteArray :
static const char mydata[] = { '\x00', '\x00', '\x03', '\x84', '\x78', '\x9c', '\x3b', '\x76', '\xec', '\x18', '\xc3', '\x31', '\x0a', '\xf1', '\xcc', '\x99', ... '\x6d', '\x5b' }; QByteArray data = QByteArray::fromRawData(mydata, sizeof(mydata)); QDataStream in(&data, QIODevice::ReadOnly); ...
警告：
A byte array created with fromRawData() is
not
null-terminated, unless the raw data contains a 0 character at position
size
. While that does not matter for
QDataStream
or functions like
indexOf
(), passing the byte array to a function accepting a
const char *
expected to be '\0'-terminated will fail.
另請參閱 setRawData (), data ()，和 constData ().
[static]
QByteArray
QByteArray::
fromRawNSData
(const
NSData
*
data
)
構造 QByteArray that uses the bytes of the NSData data .
The data 的字節不拷貝。
The caller guarantees that the NSData will not be deleted or modified as long as this QByteArray object exists.
該函數在 Qt 5.3 引入。
另請參閱 fromNSData (), fromRawData (), toRawNSData ()，和 toNSData ().
[static]
QByteArray
QByteArray::
fromStdString
(const
std::string
&
str
)
返迴副本為 str string as a QByteArray .
該函數在 Qt 5.4 引入。
另請參閱 toStdString () 和 QString::fromStdString ().
Returns the first character in the byte array. Same as
at(0)
.
此函數為兼容 STL (標準模闆庫) 提供。
警告： 空字節數組調用此函數，會構成未定義行為。
該函數在 Qt 5.10 引入。
另請參閱 back (), at ()，和 operator[] ().
Returns a reference to the first character in the byte array. Same as
operator[](0)
.
此函數為兼容 STL (標準模闆庫) 提供。
警告： 空字節數組調用此函數，會構成未定義行為。
該函數在 Qt 5.10 引入。
另請參閱 back (), at ()，和 operator[] ().
Returns the index position of the first occurrence of the byte array ba in this byte array, searching forward from index position from . Returns -1 if ba could not be found.
範例：
QByteArray x("sticky question"); QByteArray 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
另請參閱 lastIndexOf (), contains ()，和 count ().
這是重載函數。
Returns the index position of the first occurrence of the string str in the byte array, searching forward from index position from . Returns -1 if str could not be found.
這是重載函數。
Returns the index position of the first occurrence of the character ch in the byte array, searching forward from index position from . Returns -1 if ch could not be found.
範例：
QByteArray ba("ABCBA"); ba.indexOf("B"); // returns 1 ba.indexOf("B", 1); // returns 1 ba.indexOf("B", 2); // returns 3 ba.indexOf("X"); // returns -1
另請參閱 lastIndexOf () 和 contains ().
這是重載函數。
Returns the index position of the first occurrence of the string str in the byte array, searching forward from index position from . Returns -1 if str could not be found.
The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
可以禁用此函數通過定義
QT_NO_CAST_TO_ASCII
當編譯應用程序時。那麼需要調用
QString::toUtf8
() (或
QString::toLatin1
() 或
QString::toLocal8Bit
()) explicitly if you want to convert the data to
const char *
.
Inserts the byte array ba at index position i and returns a reference to this byte array.
範例：
QByteArray ba("Meal"); ba.insert(1, QByteArray("ontr")); // ba == "Montreal"
另請參閱 append (), prepend (), replace ()，和 remove ().
這是重載函數。
插入 count copies of character ch at index position i 在字節數組中。
若 i 大於 size (), the array is first extended using resize ().
該函數在 Qt 5.7 引入。
這是重載函數。
插入字符串 str 在位置 i 在字節數組中。
若 i 大於 size (), the array is first extended using resize ().
這是重載函數。
插入 len bytes of the string str 在位置 i 在字節數組中。
若 i 大於 size (), the array is first extended using resize ().
該函數在 Qt 4.6 引入。
這是重載函數。
Inserts character ch at index position i in the byte array. If i 大於 size (), the array is first extended using resize ().
這是重載函數。
插入字符串 str at index position i in the byte array. The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
若 i 大於 size (), the array is first extended using resize ().
可以禁用此函數通過定義
QT_NO_CAST_TO_ASCII
當編譯應用程序時。那麼需要調用
QString::toUtf8
() (或
QString::toLatin1
() 或
QString::toLocal8Bit
()) explicitly if you want to convert the data to
const char *
.
返迴
true
if the byte array has size 0; otherwise returns
false
.
範例：
QByteArray().isEmpty(); // returns true QByteArray("").isEmpty(); // returns true QByteArray("abc").isEmpty(); // returns false
另請參閱 size ().
返迴
true
if this byte array contains only lowercase letters, otherwise returns
false
. The byte array is interpreted as a Latin-1 encoded string.
該函數在 Qt 5.12 引入。
返迴
true
if this byte array is null; otherwise returns
false
.
範例：
QByteArray().isNull(); // returns true QByteArray("").isNull(); // returns false QByteArray("abc").isNull(); // returns false
Qt makes a distinction between null byte arrays and empty byte arrays for historical reasons. For most applications, what matters is whether or not a byte array contains any data, and this can be determined using isEmpty ().
另請參閱 isEmpty ().
返迴
true
if this byte array contains only uppercase letters, otherwise returns
false
. The byte array is interpreted as a Latin-1 encoded string.
該函數在 Qt 5.12 引入。
Returns the index position of the last occurrence of the byte array ba in this byte array, searching backward from index position from 。若 from is -1 (the default), the search starts at the last byte. Returns -1 if ba could not be found.
範例：
QByteArray x("crazy azimuths"); QByteArray 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 ().
這是重載函數。
Returns the index position of the last occurrence of the string str in the byte array, searching backward from index position from 。若 from is -1 (the default), the search starts at the last ( size () - 1) byte. Returns -1 if str could not be found.
這是重載函數。
Returns the index position of the last occurrence of character ch in the byte array, searching backward from index position from 。若 from is -1 (the default), the search starts at the last ( size () - 1) byte. Returns -1 if ch could not be found.
範例：
QByteArray ba("ABCBA"); ba.lastIndexOf("B"); // returns 3 ba.lastIndexOf("B", 3); // returns 3 ba.lastIndexOf("B", 2); // returns 1 ba.lastIndexOf("X"); // returns -1
另請參閱 indexOf () 和 contains ().
這是重載函數。
Returns the index position of the last occurrence of the string str in the byte array, searching backward from index position from 。若 from is -1 (the default), the search starts at the last ( size () - 1) byte. Returns -1 if str could not be found.
The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
可以禁用此函數通過定義
QT_NO_CAST_TO_ASCII
當編譯應用程序時。那麼需要調用
QString::toUtf8
() (或
QString::toLatin1
() 或
QString::toLocal8Bit
()) explicitly if you want to convert the data to
const char *
.
返迴的字節數組包含最左 len 字節對於此字節數組。
返迴整個字節數組若 len 大於 size ().
範例：
QByteArray x("Pineapple"); QByteArray y = x.left(4); // y == "Pine"
另請參閱 startsWith (), right (), mid (), chopped (), chop ()，和 truncate ().
Returns a byte array of size width that contains this byte array padded by the fill character.
若 truncate is false and the size () of the byte array is more than width , then the returned byte array is a copy of this byte array.
若 truncate is true and the size () of the byte array is more than width , then any bytes in a copy of the byte array after position width are removed, and the copy is returned.
範例：
QByteArray x("apple"); QByteArray y = x.leftJustified(8, '.'); // y == "apple..."
另請參閱 rightJustified ().
如同 size ().
返迴的字節數組包含 len 字節從此字節數組，起始於位置 pos .
若 len 為 -1 (默認)，或 pos + len >= size (), returns a byte array containing all bytes starting at position pos until the end of the byte array.
範例：
QByteArray x("Five pineapples"); QByteArray y = x.mid(5, 4); // y == "pine" QByteArray z = x.mid(5); // z == "pineapples"
另請參閱 left (), right (), chopped (), chop ()，和 truncate ().
[static]
QByteArray
QByteArray::
number
(
int
n
,
int
base
= 10)
Returns a byte array containing the string equivalent of the number n to base base (10 by default). The base can be any value between 2 and 36.
範例：
int n = 63; QByteArray::number(n); // returns "63" QByteArray::number(n, 16); // returns "3f" QByteArray::number(n, 16).toUpper(); // returns "3F"
注意： The format of the number is not localized; the default C locale is used irrespective of the user's locale.
[static]
QByteArray
QByteArray::
number
(
uint
n
,
int
base
= 10)
這是重載函數。
另請參閱 toUInt ().
[static]
QByteArray
QByteArray::
number
(
qlonglong
n
,
int
base
= 10)
這是重載函數。
另請參閱 toLongLong ().
[static]
QByteArray
QByteArray::
number
(
qulonglong
n
,
int
base
= 10)
這是重載函數。
另請參閱 toULongLong ().
[static]
QByteArray
QByteArray::
number
(
double
n
,
char
f
= 'g',
int
prec
= 6)
這是重載函數。
Returns a byte array that contains the printed value of n , formatted in format f with precision prec .
自變量
n
is formatted according to the
f
format specified, which is
g
by default, and can be any of the following:
| 格式 | 含義 |
|---|---|
e
|
format as [-]9.9e[+|-]999 |
E
|
format as [-]9.9E[+|-]999 |
f
|
format as [-]9.9 |
g
|
使用
e
or
f
format, whichever is the most concise
|
G
|
使用
E
or
f
format, whichever is the most concise
|
With 'e', 'E', and 'f', prec is the number of digits after the decimal point. With 'g' and 'G', prec is the maximum number of significant digits (trailing zeroes are omitted).
QByteArray ba = QByteArray::number(12.3456, 'E', 3); // ba == 1.235E+01
注意： The format of the number is not localized; the default C locale is used irrespective of the user's locale.
另請參閱 toDouble ().
前置字節數組 ba 到此字節數組，並返迴此字節數組的引用。
範例：
QByteArray x("ship"); QByteArray y("air"); x.prepend(y); // x == "airship"
這如同 insert(0, ba ).
注意： QByteArray 是 隱式共享 class. Consequently, if you prepend to an empty byte array, then the byte array will just share the data held in ba 。在這種情況下，不進行數據拷貝，花費 常量時間 。若共享實例被修改，它將被拷貝 (寫時拷貝)，花費 綫性時間 .
If the byte array being prepended to is not empty, a deep copy of the data is performed, taking 綫性時間 .
這是重載函數。
前置 count copies of character ch 到此字節數組。
該函數在 Qt 5.7 引入。
這是重載函數。
前置字符串 str 到此字節數組。
這是重載函數。
前置 len bytes of the string str 到此字節數組。
該函數在 Qt 4.6 引入。
這是重載函數。
前置字符 ch 到此字節數組。
This function is provided for STL compatibility. It is equivalent to append( other ).
這是重載函數。
如同 append( str ).
這是重載函數。
如同 append( ch ).
This function is provided for STL compatibility. It is equivalent to prepend( other ).
這是重載函數。
如同 prepend( str ).
這是重載函數。
如同 prepend( ch ).
返迴 STL-style reverse iterator pointing to the first character in the byte-array, in reverse order.
該函數在 Qt 5.6 引入。
另請參閱 begin (), crbegin ()，和 rend ().
這是重載函數。
該函數在 Qt 5.6 引入。
移除 len bytes from the array, starting at index position pos , and returns a reference to the array.
若 pos is out of range, nothing happens. If pos is valid, but pos + len is larger than the size of the array, the array is truncated at position pos .
範例：
QByteArray ba("Montreal"); ba.remove(1, 4); // ba == "Meal"
返迴 STL-style reverse iterator pointing to one past the last character in the byte-array, in reverse order.
該函數在 Qt 5.6 引入。
另請參閱 end (), crend ()，和 rbegin ().
這是重載函數。
該函數在 Qt 5.6 引入。
Returns a copy of this byte array repeated the specified number of times .
若 times is less than 1, an empty byte array is returned.
範例：
QByteArray ba("ab"); ba.repeated(4); // returns "abababab"
該函數在 Qt 4.5 引入。
替換 len bytes from index position pos with the byte array after , and returns a reference to this byte array.
範例：
QByteArray x("Say yes!"); QByteArray y("no"); x.replace(4, 3, y); // x == "Say no!"
這是重載函數。
替換 len bytes from index position pos with alen bytes from the string after . after is allowed to have '\0' characters.
該函數在 Qt 4.7 引入。
這是重載函數。
替換 len bytes from index position pos with the zero terminated string after .
注意：這可以改變字節數組的長度。
這是重載函數。
Replaces every occurrence of the character before 采用字符串 after .
這是重載函數。
Replaces every occurrence of the character before with the byte array after .
這是重載函數。
Replaces every occurrence of the string before 采用字符串 after .
這是重載函數。
Replaces every occurrence of the string before 采用字符串 after . Since the sizes of the strings are given by bsize and asize , they may contain zero characters and do not need to be zero-terminated.
這是重載函數。
Replaces every occurrence of the byte array before with the byte array after .
範例：
QByteArray ba("colour behaviour flavour neighbour"); ba.replace(QByteArray("ou"), QByteArray("o")); // ba == "color behavior flavor neighbor"
這是重載函數。
Replaces every occurrence of the byte array before 采用字符串 after .
這是重載函數。
Replaces every occurrence of the string before with the byte array after .
這是重載函數。
Replaces every occurrence of the character before with the character after .
這是重載函數。
Replaces every occurrence of the string before 采用字符串 after .
這是重載函數。
Replaces every occurrence of the character before 采用字符串 after . The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
可以禁用此函數通過定義
QT_NO_CAST_TO_ASCII
當編譯應用程序時。那麼需要調用
QString::toUtf8
() (或
QString::toLatin1
() 或
QString::toLocal8Bit
()) explicitly if you want to convert the data to
const char *
.
這是重載函數。
Replaces every occurrence of the string before with the byte array after . The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
可以禁用此函數通過定義
QT_NO_CAST_TO_ASCII
當編譯應用程序時。那麼需要調用
QString::toUtf8
() (或
QString::toLatin1
() 或
QString::toLocal8Bit
()) explicitly if you want to convert the data to
const char *
.
試圖分配內存為至少 size bytes. If you know in advance how large the byte array will be, you can call this function, and if you call resize () often you are likely to get better performance. If size is an underestimate, the worst that will happen is that the QByteArray will be a bit slower.
The sole purpose of this function is to provide a means of fine tuning QByteArray 's memory usage. In general, you will rarely ever need to call this function. If you want to change the size of the byte array, call resize ().
另請參閱 squeeze () 和 capacity ().
把字節數組的尺寸設為 size 字節。
若 size is greater than the current size, the byte array is extended to make it size bytes with the extra bytes added to the end. The new bytes are uninitialized.
若 size is less than the current size, bytes are removed from the end.
返迴的字節數組包含最右 len 字節對於此字節數組。
返迴整個字節數組若 len 大於 size ().
範例：
QByteArray x("Pineapple"); QByteArray y = x.right(5); // y == "apple"
另請參閱 endsWith (), left (), mid (), chopped (), chop ()，和 truncate ().
Returns a byte array of size width 包含 fill character followed by this byte array.
若 truncate is false and the size of the byte array is more than width , then the returned byte array is a copy of this byte array.
若 truncate is true and the size of the byte array is more than width , then the resulting byte array is truncated at position width .
範例：
QByteArray x("apple"); QByteArray y = x.rightJustified(8, '.'); // y == "...apple"
另請參閱 leftJustified ().
Sets the byte array to the printed value of n in base base (10 by default) and returns a reference to the byte array. The base can be any value between 2 and 36. For bases other than 10, n is treated as an unsigned integer.
範例：
QByteArray ba; int n = 63; ba.setNum(n); // ba == "63" ba.setNum(n, 16); // ba == "3f"
注意： The format of the number is not localized; the default C locale is used irrespective of the user's locale.
這是重載函數。
另請參閱 toUShort ().
這是重載函數。
另請參閱 toShort ().
這是重載函數。
另請參閱 toUInt ().
這是重載函數。
另請參閱 toLongLong ().
這是重載函數。
另請參閱 toULongLong ().
這是重載函數。
Sets the byte array to the printed value of n , formatted in format f with precision prec , and returns a reference to the byte array.
注意： The format of the number is not localized; the default C locale is used irrespective of the user's locale.
另請參閱 toFloat ().
這是重載函數。
Sets the byte array to the printed value of n , formatted in format f with precision prec , and returns a reference to the byte array.
格式 f 可以是下列任一：
| 格式 | 含義 |
|---|---|
e
|
format as [-]9.9e[+|-]999 |
E
|
format as [-]9.9E[+|-]999 |
f
|
format as [-]9.9 |
g
|
使用
e
or
f
format, whichever is the most concise
|
G
|
使用
E
or
f
format, whichever is the most concise
|
With 'e', 'E', and 'f', prec is the number of digits after the decimal point. With 'g' and 'G', prec is the maximum number of significant digits (trailing zeroes are omitted).
注意： The format of the number is not localized; the default C locale is used irrespective of the user's locale.
另請參閱 toDouble ().
Resets the QByteArray to use the first size bytes of the data array. The bytes are not copied. The QByteArray will contain the data pointer. The caller guarantees that data will not be deleted or modified as long as this QByteArray and any copies of it exist that have not been modified.
This function can be used instead of fromRawData () to re-use existing QByteArray objects to save memory re-allocations.
該函數在 Qt 4.7 引入。
另請參閱 fromRawData (), data ()，和 constData ().
此函數為兼容 STL (標準模闆庫) 提供。它相當於 squeeze ().
該函數在 Qt 5.10 引入。
Returns a byte array that has whitespace removed from the start and the end, and which has each sequence of internal whitespace replaced with a single space.
Whitespace means any character for which the standard C++
isspace()
函數返迴
true
in the C locale. This includes the ASCII isspace() function returns
true
in the C locale. This includes the ASCII characters '\t', '\n', '\v', '\f', '\r', and ' '.
範例：
QByteArray ba(" lots\t of\nwhitespace\r\n "); ba = ba.simplified(); // ba == "lots of whitespace";
另請參閱 trimmed ().
返迴此字節數組的字節數。
The last byte in the byte array is at position size() - 1. In addition, QByteArray ensures that the byte at position size() is always '\0', so that you can use the return value of data () 和 constData () as arguments to functions that expect '\0'-terminated strings. If the QByteArray object was created from a raw data that didn't include the trailing null-termination character then QByteArray doesn't add it automaticall unless the 深拷貝 被創建。
範例：
QByteArray ba("Hello"); int n = ba.size(); // n == 5 ba.data()[0]; // returns 'H' ba.data()[4]; // returns 'o' ba.data()[5]; // returns '\0'
Splits the byte array into subarrays wherever sep occurs, and returns the list of those arrays. If sep does not match anywhere in the byte array, split() returns a single-element list containing this byte array.
Releases any memory not required to store the array's data.
The sole purpose of this function is to provide a means of fine tuning QByteArray 's memory usage. In general, you will rarely ever need to call this function.
另請參閱 reserve () 和 capacity ().
返迴
true
若此字節數組開頭采用字節數組
ba
；否則返迴
false
.
範例：
QByteArray url("ftp://ftp.qt-project.org/"); if (url.startsWith("ftp:")) ...
這是重載函數。
返迴
true
if this byte array starts with character
ch
；否則返迴
false
.
這是重載函數。
返迴
true
if this byte array starts with string
str
；否則返迴
false
.
交換字節數組 other with this byte array. This operation is very fast and never fails.
該函數在 Qt 4.8 引入。
Returns a copy of the byte array, encoded as Base64.
QByteArray text("Qt is great!"); text.toBase64(); // returns "UXQgaXMgZ3JlYXQh"
The algorithm used to encode Base64-encoded data is defined in RFC 4648 .
另請參閱 fromBase64 ().
這是重載函數。
返迴字節數組的副本，編碼使用選項 options .
QByteArray text("<p>Hello?</p>"); text.toBase64(QByteArray::Base64Encoding | QByteArray::OmitTrailingEquals); // returns "PHA+SGVsbG8/PC9wPg" text.toBase64(QByteArray::Base64Encoding); // returns "PHA+SGVsbG8/PC9wPg==" text.toBase64(QByteArray::Base64UrlEncoding); // returns "PHA-SGVsbG8_PC9wPg==" text.toBase64(QByteArray::Base64UrlEncoding | QByteArray::OmitTrailingEquals); // returns "PHA-SGVsbG8_PC9wPg"
The algorithm used to encode Base64-encoded data is defined in RFC 4648 .
該函數在 Qt 5.2 引入。
另請參閱 fromBase64 ().
創建 CFData 從 QByteArray . The caller owns the CFData object and is responsible for releasing it.
該函數在 Qt 5.3 引入。
另請參閱 toRawCFData (), fromCFData (), fromRawCFData ()，和 fromRawData ().
返迴字節數組被轉換成
double
值。
Returns an infinity if the conversion overflows or 0.0 if the conversion fails for other reasons (e.g. underflow).
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
QByteArray string("1234.56"); bool ok; double a = string.toDouble(&ok); // a == 1234.56, ok == true string = "1234.56 Volt"; a = str.toDouble(&ok); // a == 0, ok == false
警告： The QByteArray content may only contain valid numerical characters which includes the plus/minus sign, the character e used in scientific notation, and the decimal point. Including the unit or additional characters leads to a conversion error.
注意： The conversion of the number is performed in the default C locale, irrespective of the user's locale.
此函數忽略前導和結尾空格。
另請參閱 number ().
返迴字節數組被轉換成
float
值。
Returns an infinity if the conversion overflows or 0.0 if the conversion fails for other reasons (e.g. underflow).
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
QByteArray string("1234.56"); bool ok; float a = string.toFloat(&ok); // a == 1234.56, ok == true string = "1234.56 Volt"; a = str.toFloat(&ok); // a == 0, ok == false
警告： The QByteArray content may only contain valid numerical characters which includes the plus/minus sign, the character e used in scientific notation, and the decimal point. Including the unit or additional characters leads to a conversion error.
注意： The conversion of the number is performed in the default C locale, irrespective of the user's locale.
此函數忽略前導和結尾空格。
另請參閱 number ().
Returns a hex encoded copy of the byte array. The hex encoding uses the numbers 0-9 and the letters a-f.
另請參閱 fromHex ().
這是重載函數。
Returns a hex encoded copy of the byte array. The hex encoding uses the numbers 0-9 and the letters a-f.
若 separator is not '\0', the separator character is inserted between the hex bytes.
範例：
QByteArray macAddress = QByteArray::fromHex("123456abcdef"); macAddress.toHex(':'); // returns "12:34:56:ab:cd:ef" macAddress.toHex(0); // returns "123456abcdef"
該函數在 Qt 5.9 引入。
另請參閱 fromHex ().
返迴字節數組被轉換成
int
使用基
base
, which is 10 by default and must be between 2 and 36, or 0.
若 base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.
返迴 0，若轉換失敗。
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
QByteArray str("FF"); bool ok; int hex = str.toInt(&ok, 16); // hex == 255, ok == true int dec = str.toInt(&ok, 10); // dec == 0, ok == false
注意： The conversion of the number is performed in the default C locale, irrespective of the user's locale.
另請參閱 number ().
返迴字節數組被轉換成
long
int using base
base
, which is 10 by default and must be between 2 and 36, or 0.
若 base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.
返迴 0，若轉換失敗。
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
QByteArray str("FF"); bool ok; long hex = str.toLong(&ok, 16); // hex == 255, ok == true long dec = str.toLong(&ok, 10); // dec == 0, ok == false
注意： The conversion of the number is performed in the default C locale, irrespective of the user's locale.
該函數在 Qt 4.1 引入。
另請參閱 number ().
返迴字節數組被轉換成
long long
使用基
base
, which is 10 by default and must be between 2 and 36, or 0.
若 base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.
返迴 0，若轉換失敗。
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
注意： The conversion of the number is performed in the default C locale, irrespective of the user's locale.
另請參閱 number ().
Returns a lowercase copy of the byte array. The bytearray is interpreted as a Latin-1 encoded string.
範例：
QByteArray x("Qt by THE QT COMPANY"); QByteArray y = x.toLower(); // y == "qt by the qt company"
另請參閱 isLower (), toUpper ()，和 8 位字符比較 .
創建 NSData 從 QByteArray . The NSData object is autoreleased.
該函數在 Qt 5.3 引入。
另請參閱 fromNSData (), fromRawNSData (), fromRawData ()，和 toRawNSData ().
Returns a URI/URL-style percent-encoded copy of this byte array. The percent parameter allows you to override the default '%' character for another.
By default, this function will encode all characters that are not one of the following:
ALPHA ("a" to "z" and "A" to "Z") / DIGIT (0 to 9) / "-" / "." / "_" / "~"
To prevent characters from being encoded pass them to exclude . To force characters to be encoded pass them to 包括 。 percent character is always encoded.
範例：
QByteArray text = "{a fishy string?}"; QByteArray ba = text.toPercentEncoding("{}", "s"); qDebug(ba.constData()); // prints "{a fi%73hy %73tring%3F}"
The hex encoding uses the numbers 0-9 and the uppercase letters A-F.
該函數在 Qt 4.4 引入。
另請參閱 fromPercentEncoding () 和 QUrl::toPercentEncoding ().
Constructs a CFData that uses the bytes of the QByteArray .
The QByteArray 的字節不拷貝。
The caller guarantees that the QByteArray will not be deleted or modified as long as this CFData object exists.
該函數在 Qt 5.3 引入。
另請參閱 toCFData (), fromRawCFData (), fromCFData ()，和 fromRawData ().
Constructs a NSData that uses the bytes of the QByteArray .
The QByteArray 的字節不拷貝。
The caller guarantees that the QByteArray will not be deleted or modified as long as this NSData object exists.
該函數在 Qt 5.3 引入。
另請參閱 fromRawNSData (), fromNSData (), fromRawData ()，和 toNSData ().
返迴字節數組被轉換成
short
使用基
base
, which is 10 by default and must be between 2 and 36, or 0.
若 base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.
返迴 0，若轉換失敗。
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
注意： The conversion of the number is performed in the default C locale, irrespective of the user's locale.
另請參閱 number ().
返迴 std::string 對象帶有的數據包含在此 QByteArray .
此運算符主要用於傳遞 QByteArray 到接受 std::string 對象的函數。
該函數在 Qt 5.4 引入。
另請參閱 fromStdString () 和 QString::toStdString ().
返迴字節數組被轉換成
無符號 int
使用基
base
, which is 10 by default and must be between 2 and 36, or 0.
若 base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.
返迴 0，若轉換失敗。
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
注意： The conversion of the number is performed in the default C locale, irrespective of the user's locale.
另請參閱 number ().
返迴字節數組被轉換成
unsigned long int
使用基
base
, which is 10 by default and must be between 2 and 36, or 0.
若 base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.
返迴 0，若轉換失敗。
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
注意： The conversion of the number is performed in the default C locale, irrespective of the user's locale.
該函數在 Qt 4.1 引入。
另請參閱 number ().
返迴字節數組被轉換成
unsigned long long
使用基
base
, which is 10 by default and must be between 2 and 36, or 0.
若 base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.
返迴 0，若轉換失敗。
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
注意： The conversion of the number is performed in the default C locale, irrespective of the user's locale.
另請參閱 number ().
返迴字節數組被轉換成
unsigned short
使用基
base
, which is 10 by default and must be between 2 and 36, or 0.
若 base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.
返迴 0，若轉換失敗。
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
注意： The conversion of the number is performed in the default C locale, irrespective of the user's locale.
另請參閱 number ().
Returns an uppercase copy of the byte array. The bytearray is interpreted as a Latin-1 encoded string.
範例：
QByteArray x("Qt by THE QT COMPANY"); QByteArray y = x.toUpper(); // y == "QT BY THE QT COMPANY"
另請參閱 isUpper (), toLower ()，和 8 位字符比較 .
Returns a byte array that has whitespace removed from the start and the end.
Whitespace means any character for which the standard C++
isspace()
函數返迴
true
in the C locale. This includes the ASCII characters '\t', '\n', '\v', '\f', '\r', and ' '.
範例：
QByteArray ba(" lots\t of\nwhitespace\r\n "); ba = ba.trimmed(); // ba == "lots\t of\nwhitespace";
不像 simplified ()，trimmed() 隻留下內部空白。
另請參閱 simplified ().
截取字節數組按索引位置 pos .
若 pos 超越數組末尾，什麼都不發生。
範例：
QByteArray ba("Stockholm"); ba.truncate(5); // ba == "Stock"
另請參閱 chop (), resize ()，和 left ().
返迴
true
if this byte array is not equal to string
str
；否則返迴
false
.
The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
比較是區分大小寫的。
可以禁用此運算符通過定義
QT_NO_CAST_FROM_ASCII
當編譯應用程序時。那麼需要調用
QString::fromUtf8
(),
QString::fromLatin1
()，或
QString::fromLocal8Bit
() explicitly if you want to convert the byte array to a
QString
before doing the comparison.
追加字節數組 ba onto the end of this byte array and returns a reference to this byte array.
範例：
QByteArray x("free"); QByteArray y("dom"); x += y; // x == "freedom"
注意： QByteArray 是 隱式共享 類。因此，若追加到空字節數組，那麼字節數組將僅僅共享的數據保持在 ba 。在這種情況下，不進行數據拷貝，花費 常量時間 。若共享實例被修改，它將被拷貝 (寫時拷貝)，花費 綫性時間 .
若要追加到的字節數組非空，履行數據深拷貝，花費 綫性時間 .
This operation typically does not suffer from allocation overhead, because QByteArray preallocates extra space at the end of the data so that it may grow without reallocating for each append operation.
這是重載函數。
追加字符串 str onto the end of this byte array and returns a reference to this byte array.
這是重載函數。
追加字符 ch onto the end of this byte array and returns a reference to this byte array.
這是重載函數。
追加字符串 str onto the end of this byte array and returns a reference to this byte array. The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
可以禁用此函數通過定義
QT_NO_CAST_TO_ASCII
當編譯應用程序時。那麼需要調用
QString::toUtf8
() (或
QString::toLatin1
() 或
QString::toLocal8Bit
()) explicitly if you want to convert the data to
const char *
.
返迴
true
if this byte array is lexically less than string
str
；否則返迴
false
.
The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
比較是區分大小寫的。
可以禁用此運算符通過定義
QT_NO_CAST_FROM_ASCII
當編譯應用程序時。那麼需要調用
QString::fromUtf8
(),
QString::fromLatin1
()，或
QString::fromLocal8Bit
() explicitly if you want to convert the byte array to a
QString
before doing the comparison.
返迴
true
if this byte array is lexically less than or equal to string
str
；否則返迴
false
.
The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
比較是區分大小寫的。
可以禁用此運算符通過定義
QT_NO_CAST_FROM_ASCII
當編譯應用程序時。那麼需要調用
QString::fromUtf8
(),
QString::fromLatin1
()，或
QString::fromLocal8Bit
() explicitly if you want to convert the byte array to a
QString
before doing the comparison.
賦值 other 到此字節數組，並返迴此字節數組的引用。
這是重載函數。
賦值 str 到此字節數組。
移動賦值 other 到此 QByteArray 實例。
該函數在 Qt 5.2 引入。
返迴
true
if this byte array is equal to string
str
；否則返迴
false
.
The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
比較是區分大小寫的。
可以禁用此運算符通過定義
QT_NO_CAST_FROM_ASCII
當編譯應用程序時。那麼需要調用
QString::fromUtf8
(),
QString::fromLatin1
()，或
QString::fromLocal8Bit
() explicitly if you want to convert the byte array to a
QString
before doing the comparison.
返迴
true
if this byte array is lexically greater than string
str
；否則返迴
false
.
The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
比較是區分大小寫的。
可以禁用此運算符通過定義
QT_NO_CAST_FROM_ASCII
當編譯應用程序時。那麼需要調用
QString::fromUtf8
(),
QString::fromLatin1
()，或
QString::fromLocal8Bit
() explicitly if you want to convert the byte array to a
QString
before doing the comparison.
返迴
true
if this byte array is greater than or equal to string
str
；否則返迴
false
.
The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
比較是區分大小寫的。
可以禁用此運算符通過定義
QT_NO_CAST_FROM_ASCII
當編譯應用程序時。那麼需要調用
QString::fromUtf8
(),
QString::fromLatin1
()，或
QString::fromLocal8Bit
() explicitly if you want to convert the byte array to a
QString
before doing the comparison.
返迴字節按索引位置 i 作為可修改引用。
If an assignment is made beyond the end of the byte array, the array is extended with resize () before the assignment takes place.
範例：
QByteArray ba; for (int i = 0; i < 10; ++i) ba[i] = 'A' + i; // ba == "ABCDEFGHIJ"
The return value is of type QByteRef, a helper class for QByteArray . When you get an object of type QByteRef, you can use it as if it were a char &. If you assign to it, the assignment will apply to the character in the QByteArray from which you got the reference.
另請參閱 at ().
這是重載函數。
這是重載函數。
如同 at( i ).
這是重載函數。
Returns the CRC-16 checksum of the first len bytes of data .
The checksum is independent of the byte order (endianness) and will be calculated accorded to the algorithm published in ISO 3309 ( Qt::ChecksumIso3309 ).
注意： This function is a 16-bit cache conserving (16 entry table) implementation of the CRC-16-CCITT algorithm.
Returns the CRC-16 checksum of the first len bytes of data .
The checksum is independent of the byte order (endianness) and will be calculated accorded to the algorithm published in standard .
注意： This function is a 16-bit cache conserving (16 entry table) implementation of the CRC-16-CCITT algorithm.
該函數在 Qt 5.9 引入。
這是重載函數。
Compresses the first nbytes of data at compression level compressionLevel and returns the compressed data in a new byte array.
Compresses the data byte array and returns the compressed data in a new byte array.
The compressionLevel parameter specifies how much compression should be used. Valid values are between 0 and 9, with 9 corresponding to the greatest compression (i.e. smaller compressed data) at the cost of using a slower algorithm. Smaller values (8, 7, ..., 1) provide successively less compression at slightly faster speeds. The value 0 corresponds to no compression at all. The default value is -1, which specifies zlib's default compression.
另請參閱 qUncompress ().
這是重載函數。
Uncompresses the first nbytes of data and returns a new byte array with the uncompressed data.
Uncompresses the data byte array and returns a new byte array with the uncompressed data.
返迴空 QByteArray 若輸入數據被破壞。
This function will uncompress data compressed with qCompress () from this and any earlier Qt version, back to Qt 3.1 when this feature was added.
注意： If you want to use this function to uncompress external data that was compressed using zlib, you first need to prepend a four byte header to the byte array containing the data. The header must contain the expected length (in bytes) of the uncompressed data, expressed as an unsigned, big-endian, 32-bit integer.
另請參閱 qCompress ().
可移植 snprintf() 函數，調用 qvsnprintf。
fmt
是
printf()
format string. The result is put into
str
, which is a buffer of at least
n
字節。
警告： Call this function only when you know what you are doing since it shows different behavior on certain platforms. Use QString::asprintf () to format a string instead.
另請參閱 qvsnprintf () 和 QString::asprintf ().
安全
strcmp()
函數。
比較 str1 and str2 。返迴負值若 str1 小於 str2 , 0 if str1 等於 str2 或正值若 str1 大於 str2 .
特殊情況 1：返迴 0 若 str1 and str2 are both nullptr.
Special case 2: Returns an arbitrary non-zero value if str1 is nullptr or str2 is nullptr (but not both).
另請參閱 qstrncmp (), qstricmp (), qstrnicmp (), 8 位字符比較 ，和 QByteArray::compare ().
Copies all the characters up to and including the '\0' from src into dst and returns a pointer to dst 。若 src is nullptr, it immediately returns nullptr.
This function assumes that dst is large enough to hold the contents of src .
注意： 若 dst and src overlap, the behavior is undefined.
另請參閱 qstrncpy ().
返迴復製字符串。
Allocates space for a copy of src , copies it, and returns a pointer to the copy. If src is nullptr, it immediately returns nullptr.
Ownership is passed to the caller, so the returned string must be deleted using
delete[]
.
安全
stricmp()
函數。
比較 str1 and str2 ignoring the case of the characters. The encoding of the strings is assumed to be Latin-1.
Returns a negative value if str1 小於 str2 , 0 if str1 等於 str2 或正值若 str1 大於 str2 .
特殊情況 1：返迴 0 若 str1 and str2 are both nullptr.
Special case 2: Returns a random non-zero value if str1 is nullptr or str2 is nullptr (but not both).
另請參閱 qstrcmp (), qstrncmp (), qstrnicmp (), 8 位字符比較 ，和 QByteArray::compare ().
安全
strlen()
函數。
Returns the number of characters that precede the terminating '\0', or 0 if str is nullptr.
另請參閱 qstrnlen ().
安全
strncmp()
函數。
比較最多 len bytes of str1 and str2 .
Returns a negative value if str1 小於 str2 , 0 if str1 等於 str2 或正值若 str1 大於 str2 .
特殊情況 1：返迴 0 若 str1 and str2 are both nullptr.
Special case 2: Returns a random non-zero value if str1 is nullptr or str2 is nullptr (but not both).
另請參閱 qstrcmp (), qstricmp (), qstrnicmp (), 8 位字符比較 ，和 QByteArray::compare ().
安全
strncpy()
函數。
拷貝最多 len 字節來自 src (stopping at len or the terminating '\0' whichever comes first) into dst and returns a pointer to dst . Guarantees that dst is '\0'-terminated. If src or dst is nullptr, returns nullptr immediately.
This function assumes that dst is at least len characters long.
注意： 若 dst and src overlap, the behavior is undefined.
注意： When compiling with Visual C++ compiler version 14.00 (Visual C++ 2005) or later, internally the function strncpy_s will be used.
另請參閱 qstrcpy ().
安全
strnicmp()
函數。
比較最多 len bytes of str1 and str2 ignoring the case of the characters. The encoding of the strings is assumed to be Latin-1.
Returns a negative value if str1 小於 str2 , 0 if str1 等於 str2 或正值若 str1 大於 str2 .
特殊情況 1：返迴 0 若 str1 and str2 are both nullptr.
Special case 2: Returns a random non-zero value if str1 is nullptr or str2 is nullptr (but not both).
另請參閱 qstrcmp (), qstrncmp (), qstricmp (), 8 位字符比較 ，和 QByteArray::compare ().
安全
strnlen()
函數。
Returns the number of characters that precede the terminating '\0', but at most maxlen 。若 str is nullptr, returns 0.
該函數在 Qt 4.2 引入。
另請參閱 qstrlen ().
可移植
vsnprintf()
函數。會調用
::vsnprintf()
,
::_vsnprintf()
，或
::vsnprintf_s
depending on the system, or fall back to an internal version.
fmt
是
printf()
format string. The result is put into
str
, which is a buffer of at least
n
字節。
The caller is responsible to call
va_end()
on
ap
.
警告： Since vsnprintf() shows different behavior on certain platforms, you should not rely on the return value or on the fact that you will always get a 0 terminated string back.
Ideally, you should never call this function but use QString::asprintf () 代替。
另請參閱 qsnprintf () 和 QString::asprintf ().
這是重載函數。
返迴
true
若字節數組
a1
不等於字節數組
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字節數組
a1
不等於字符串
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字符串
a1
不等於字節數組
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
返迴的字節數組結果是串聯字節數組 a1 和字節數組 a2 .
另請參閱 QByteArray::operator+= ().
這是重載函數。
返迴的字節數組結果是串聯字節數組 a1 and string a2 .
這是重載函數。
返迴的字節數組結果是串聯字節數組 a1 和字符 a2 .
這是重載函數。
返迴的字節數組結果是串聯字符串 a1 和字節數組 a2 .
這是重載函數。
返迴的字節數組結果是串聯字符 a1 和字節數組 a2 .
這是重載函數。
返迴
true
若字節數組
a1
詞匯上小於字節數組
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字節數組
a1
詞法上小於字符串
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字符串
a1
詞匯上小於字節數組
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
寫入字節數組 ba 到流 out 並返迴流引用。
另請參閱 序列化 Qt 數據類型 .
這是重載函數。
返迴
true
若字節數組
a1
詞法上 <= 字節數組
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字節數組
a1
詞法上 <= 字符串
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字符串
a1
詞法上 <= 字節數組
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字節數組
a1
等於字節數組
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字節數組
a1
等於字符串
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字符串
a1
等於字節數組
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字節數組
a1
詞法上大於字節數組
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字節數組
a1
詞法上大於字符串
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字符串
a1
詞法上大於字節數組
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字節數組
a1
詞法上大於等於字節數組
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字節數組
a1
詞法上大於等於字符串
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
這是重載函數。
返迴
true
若字符串
a1
詞法上大於等於字節數組
a2
；否則返迴
false
.
另請參閱 QByteArray::compare ().
讀取字節數組到 ba 從流 in 並返迴流引用。
另請參閱 序列化 Qt 數據類型 .
宏生成數據為 QByteArray 從字符串文字 ba 在編譯時。創建 QByteArray 是自由的在此情況下，且生成的字節數組數據是存儲在編譯對象文件的隻讀段中。
例如：
QByteArray ba = QByteArrayLiteral("byte array contents");
使用 QByteArrayLiteral 而不是帶雙引號的純 C++ 字符串文字可以顯著加速創建 QByteArray 實例從編譯時的已知數據。
另請參閱 QStringLiteral .
禁用自動轉換從 QByteArray 到 const char * 或 const void *。
另請參閱 QT_NO_CAST_TO_ASCII and QT_NO_CAST_FROM_ASCII .