QByteArray 类提供字节数组。 更多...
| 头： | #include <QByteArray> |
| qmake: | QT += core |
注意： 此类的所有函数 可重入 .
| class | FromBase64Result |
| enum | Base64Option { Base64Encoding, Base64UrlEncoding, KeepTrailingEquals, OmitTrailingEquals, IgnoreBase64DecodingErrors, AbortOnBase64DecodingErrors } |
| flags | Base64Options |
| typedef | const_iterator |
| typedef | const_reverse_iterator |
| typedef | iterator |
| typedef | reverse_iterator |
| QByteArray (QByteArray && other ) | |
| QByteArray (const QByteArray & other ) | |
| QByteArray (int size , char ch ) | |
| QByteArray (const char * data , int size = -1) | |
| QByteArray () | |
| QByteArray & | operator= (QByteArray && other ) |
| QByteArray & | operator= (const QByteArray & other ) |
| ~QByteArray () | |
| QByteArray & | append (const QByteArray & ba ) |
| QByteArray & | append (char ch ) |
| QByteArray & | append (int count , char ch ) |
| QByteArray & | append (const char * str ) |
| QByteArray & | append (const char * str , int len ) |
| 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 = Qt::CaseSensitive) const |
| int | compare (const QByteArray & a , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
| QByteArray::const_iterator | constBegin () const |
| const char * | constData () const |
| QByteArray::const_iterator | constEnd () const |
| bool | contains (const QByteArray & ba ) const |
| bool | contains (char ch ) const |
| bool | contains (const char * str ) const |
| int | count (const QByteArray & ba ) const |
| int | count (char ch ) const |
| int | count (const char * str ) 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 (char ch , int from = 0) const |
| int | indexOf (const char * str , int from = 0) const |
| QByteArray & | insert (int i , const QByteArray & ba ) |
| QByteArray & | insert (int i , char ch ) |
| QByteArray & | insert (int i , int count , char ch ) |
| QByteArray & | insert (int i , const char * str ) |
| QByteArray & | insert (int i , const char * str , int len ) |
| bool | isEmpty () const |
| bool | isLower () const |
| bool | isNull () const |
| bool | isUpper () const |
| int | lastIndexOf (const QByteArray & ba , int from = -1) const |
| int | lastIndexOf (char ch , int from = -1) const |
| int | lastIndexOf (const char * 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 (char ch ) |
| QByteArray & | prepend (int count , char ch ) |
| QByteArray & | prepend (const char * str ) |
| QByteArray & | prepend (const char * str , int len ) |
| void | push_back (const QByteArray & other ) |
| void | push_back (char ch ) |
| void | push_back (const char * str ) |
| void | push_front (const QByteArray & other ) |
| void | push_front (char ch ) |
| void | push_front (const char * str ) |
| 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 ) |
| QByteArray & | replace (int pos , int len , const char * after , int alen ) |
| 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 ) |
| 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 (short n , int base = 10) |
| QByteArray & | setNum (ushort 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+= (char ch ) |
| QByteArray & | operator+= (const char * str ) |
| bool | operator< (const QString & str ) const |
| bool | operator<= (const QString & str ) const |
| QByteArray & | operator= (const char * str ) |
| bool | operator== (const QString & str ) const |
| bool | operator> (const QString & str ) const |
| bool | operator>= (const QString & str ) const |
| QByteRef | operator[] (int i ) |
| char | operator[] (int i ) const |
| char | operator[] (uint i ) const |
| QByteRef | operator[] (uint i ) |
| QByteArray | fromBase64 (const QByteArray & base64 , QByteArray::Base64Options options ) |
| QByteArray | fromBase64 (const QByteArray & base64 ) |
| QByteArray::FromBase64Result | fromBase64Encoding (QByteArray && base64 , QByteArray::Base64Options options = Base64Encoding) |
| QByteArray::FromBase64Result | fromBase64Encoding (const QByteArray & base64 , QByteArray::Base64Options options = Base64Encoding) |
| 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 QByteArray & data , int compressionLevel = -1) |
| QByteArray | qCompress (const uchar * data , int nbytes , int compressionLevel = -1) |
| QByteArray | qUncompress (const QByteArray & data ) |
| QByteArray | qUncompress (const uchar * data , int nbytes ) |
| 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 |
QByteArray 可以被用于存储原生字节 (包括 \0) 和传统 8 位以 \0 结尾的字符串。使用 QByteArray 更方便比使用
const char *
。在幕后，它始终确保数据之后紧跟 \0 终止符，并使用
隐式共享
(写入时拷贝) 以缩减内存用量并避免不必要的数据拷贝。
除 QByteArray 外，Qt 还提供 QString 类以存储字符串数据。对于大多数目的， QString 是您想要使用的类。它存储 16 位 Unicode 字符，使之能在应用程序中轻松存储非 ASCII 和非 Latin-1 字符。此外， QString is used throughout in the Qt API. The two main cases where QByteArray is appropriate are when you need to store raw binary data, and when memory conservation is critical (e.g., with Qt for Embedded Linux).
One way to initialize a QByteArray is simply to pass a
const char *
到其构造函数。例如，以下代码创建包含数据 Hello 大小为 5 的字节数组：
QByteArray ba("Hello");
尽管 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]" << Qt::endl; }
at () can be faster than operator[](), because it never causes a 深拷贝 的出现。
要每次提取多个字节，使用 left (), right ()，或 mid ().
A QByteArray can embed '\0' bytes. The size () function always returns the size of the whole array, including embedded '\0' bytes, but excluding the terminating '\0' added by QByteArray. For example:
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 ().
要获得实际字符数据指针，调用 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, use 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, use 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 << Qt::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
所有函数除了 isNull () treat null byte arrays the same as empty byte arrays. For example, data () returns a valid pointer ( not nullptr) to a '\0' character for a byte array and QByteArray() compares equal to QByteArray(""). We recommend that you always use isEmpty () and avoid isNull ().
The current version of QByteArray 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.
In case memory allocation fails, QByteArray 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 QByteArray API.
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.
In QByteArray, the notion of uppercase and lowercase and of which character is greater than or less than another character is done in the Latin-1 locale. 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 Latin-1 characters. 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::IgnoreBase64DecodingErrors
|
0
|
When decoding Base64-encoded data, ignores errors in the input; invalid characters are simply skipped. This enum value has been added in Qt 5.15. |
QByteArray::AbortOnBase64DecodingErrors
|
4
|
When decoding Base64-encoded data, stops at the first decoding error. This enum value has been added in Qt 5.15. |
QByteArray::fromBase64Encoding () 和 QByteArray::fromBase64 () ignore the KeepTrailingEquals and OmitTrailingEquals options. If the IgnoreBase64DecodingErrors option is specified, they will not flag errors in case trailing equal signs are missing or if there are too many of them. If instead the AbortOnBase64DecodingErrors is specified, then the input must either have no padding or have the correct amount of equal signs.
该枚举在 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 样式 const 迭代器为 QByteArray .
另请参阅 QByteArray::const_reverse_iterator and QByteArray::iterator .
This typedef provides an STL-style const reverse iterator for QByteArray .
该 typedef 在 Qt 5.6 引入。
另请参阅 QByteArray::reverse_iterator and QByteArray::const_iterator .
This typedef provides an STL-style non-const iterator for QByteArray .
另请参阅 QByteArray::reverse_iterator and QByteArray::const_iterator .
This typedef provides an STL-style non-const reverse iterator for QByteArray .
该 typedef 在 Qt 5.6 引入。
另请参阅 QByteArray::const_reverse_iterator and QByteArray::iterator .
[static]
QByteArray::FromBase64Result
QByteArray::
fromBase64Encoding
(
QByteArray
&&
base64
,
QByteArray::Base64Options
options
= Base64Encoding)
[static]
QByteArray::FromBase64Result
QByteArray::
fromBase64Encoding
(const
QByteArray
&
base64
,
QByteArray::Base64Options
options
= Base64Encoding)
这是重载函数。
Decodes the Base64 array
base64
, using the options defined by
options
。若
options
包含
IgnoreBase64DecodingErrors
(the default), the input is not checked for validity; invalid characters in the input are skipped, enabling the decoding process to continue with subsequent characters. If
options
包含
AbortOnBase64DecodingErrors
, then decoding will stop at the first invalid character.
例如：
void process(const QByteArray &); if (auto result = QByteArray::fromBase64Encoding(encodedData)) process(*result);
The algorithm used to decode Base64-encoded data is defined in RFC 4648 .
Returns a QByteArrayFromBase64Result object, containing the decoded data and a flag telling whether decoding was successful. If the
AbortOnBase64DecodingErrors
option was passed and the input data was invalid, it is unspecified what the decoded data contains.
该函数在 Qt 5.15 引入。
另请参阅 toBase64 ().
移动构造 QByteArray 实例，使之指向同一对象如 other 所指向的。
该函数在 Qt 5.2 引入。
构造副本为 other .
此操作花费 常量时间 ，因为 QByteArray 隐式共享 . This makes returning a QByteArray from a function very fast. If a shared instance is modified, it will be copied (copy-on-write), taking 线性时间 .
另请参阅 operator= ().
构造字节数组大小为 size 采用将每字节设为字符 ch .
另请参阅 fill ().
构造字节数组包含前 size 字节的数组 data .
若 data 为 0，构造 null 字节数组。
若 size 为负， data is assumed to point to a '\0'-terminated string and its length is determined dynamically. The terminating \0 character is not considered part of the byte array.
QByteArray 制作字符串数据的深拷贝。
另请参阅 fromRawData ().
构造空字节数组。
另请参阅 isEmpty ().
移动赋值 other 到此 QByteArray 实例。
该函数在 Qt 5.2 引入。
赋值 other 到此字节数组，并返回此字节数组的引用。
销毁字节数组。
追加字节数组 ba 到此字节数组的末尾。
范例：
QByteArray x("free"); QByteArray y("dom"); x.append(y); // x == "freedom"
这如同 insert( size (), ba ).
注意： QByteArray 是 隐式共享 类。因此，若追加到空字节数组，那么字节数组将仅仅共享的数据保持在 ba 。在这种情况下，不进行数据拷贝，花费 常量时间 。若共享实例被修改，它将被拷贝 (写时拷贝)，花费 线性时间 .
若要追加到的字节数组非空，履行数据深拷贝，花费 线性时间 .
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.
另请参阅 operator+= (), prepend ()，和 insert ().
这是重载函数。
追加字符 ch 到此字节数组。
这是重载函数。
追加 count copies of character ch 到此字节数组，并返回此字节数组的引用。
若 count 为负 (或 0)，什么都不会追加到字节数组。
该函数在 Qt 5.7 引入。
这是重载函数。
追加字符串 str 到此字节数组。
此函数重载 append()。
追加第一 len characters of the string str 到此字节数组，并返回此字节数组的引用。
若 len is negative, the length of the string will be determined automatically using qstrlen ()。若 len 为 0 或 str is null, nothing is appended to the byte array. Ensure that len is not longer than str .
返回字符在索引位置 i 在字节数组中。
i 必须是字节数组中的有效索引位置 (即 0 <= i < size ()).
另请参阅 operator[] ().
Returns the last character in the byte array. Same as
at(size() - 1)
.
此函数为兼容 STL (标准模板库) 提供。
警告： 空字节数组调用此函数，会构成未定义行为。
该函数在 Qt 5.10 引入。
另请参阅 front (), at ()，和 operator[] ().
Returns a reference to the last character in the byte array. Same as
operator[](size() - 1)
.
此函数为兼容 STL (标准模板库) 提供。
警告： 空字节数组调用此函数，会构成未定义行为。
该函数在 Qt 5.10 引入。
另请参阅 front (), at ()，和 operator[] ().
返回 STL 样式迭代器 pointing to the first character in the byte-array.
另请参阅 constBegin () 和 end ().
此函数重载 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 ().
返回常量 STL 样式迭代器 pointing to the first character in the byte-array.
该函数在 Qt 5.0 引入。
返回常量 STL 样式迭代器 pointing to the imaginary character after the last character in the list.
该函数在 Qt 5.0 引入。
移除 n bytes from the end of the byte array.
若 n 大于 size (), the result is an empty byte array.
范例：
QByteArray ba("STARTTLS\r\n"); ba.chop(2); // ba == "STARTTLS"
另请参阅 truncate (), resize ()，和 left ().
返回的字节数组包含最左 size () - len 字节对于此字节数组。
注意： 行为未定义若 len 为负或大于 size ().
该函数在 Qt 5.10 引入。
另请参阅 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 .
该函数在 Qt 5.12 引入。
另请参阅 operator== .
这是重载函数。
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 .
该函数在 Qt 5.12 引入。
另请参阅 operator== .
返回常量 STL 样式迭代器 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.
此函数主要用于将字节数组传递给的函数接受
const char *
.
注意：
QByteArray
可以存储任何字节值 (包括 \0)，但大多数函数需要
char *
自变量，假定数据在遇到首个 \0 时结束。
另请参阅 data (), operator[] ()，和 fromRawData ().
返回常量 STL 样式迭代器 pointing to the imaginary character after the last character in the list.
另请参阅 constBegin () 和 end ().
返回
true
if the byte array contains an occurrence of the byte array
ba
；否则返回
false
.
这是重载函数。
返回
true
if the byte array contains the character
ch
；否则返回
false
.
这是重载函数。
返回
true
if the byte array contains the string
str
；否则返回
false
.
Returns the number of (potentially overlapping) occurrences of byte array ba in this byte array.
另请参阅 contains () 和 indexOf ().
这是重载函数。
返回出现数对于字符 ch 在字节数组中。
另请参阅 contains () 和 indexOf ().
这是重载函数。
Returns the number of (potentially overlapping) occurrences of string str 在字节数组中。
这是重载函数。
如同 size ().
返回常量 STL-style reverse iterator pointing to the first character in the byte-array, in reverse order.
该函数在 Qt 5.6 引入。
另请参阅 begin (), rbegin ()，和 rend ().
返回常量 STL-style reverse iterator pointing to one past the last character in the byte-array, in reverse order.
该函数在 Qt 5.6 引入。
另请参阅 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.
范例：
QByteArray ba("Hello world"); char *data = ba.data(); while (*data) { cout << "[" << *data << "]" << Qt::endl; ++data; }
The pointer remains valid as long as the byte array isn't reallocated or destroyed. For read-only access, constData () 更快，因为它从不导致 深拷贝 的出现。
此函数主要用于将字节数组传递给的函数接受
const char *
.
以下范例制作由 data() 返回的 char* 副本，但会破坏堆并导致崩溃，因为它没有为末尾 \0 分配字节：
QString tmp = "test"; QByteArray text = tmp.toLocal8Bit(); char *data = new char[text.size()]; strcpy(data, text.data()); delete [] data;
这个分配了正确的空间数量：
QString tmp = "test"; QByteArray text = tmp.toLocal8Bit(); char *data = new char[text.size() + 1]; strcpy(data, text.data()); delete [] data;
注意：
QByteArray
可以存储任何字节值 (包括 \0)，但大多数函数需要
char *
自变量，假定数据在遇到首个 \0 时结束。
另请参阅 constData () 和 operator[] ().
这是重载函数。
返回 STL 样式迭代器 pointing to the imaginary character after the last character in the byte-array.
此函数重载 end()。
返回
true
if this byte array ends with byte array
ba
；否则返回
false
.
范例：
QByteArray url("http://qt-project.org/doc/qt-5.0/qtdoc/index.html"); if (url.endsWith(".html")) ...
另请参阅 startsWith () 和 right ().
这是重载函数。
返回
true
if this byte array ends with character
ch
；否则返回
false
.
这是重载函数。
返回
true
if this byte array ends with string
str
；否则返回
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。
范例：
QByteArray ba("Istambul"); ba.fill('o'); // ba == "oooooooo" ba.fill('X', 2); // ba == "XX"
另请参阅 resize ().
[static]
QByteArray
QByteArray::
fromBase64
(const
QByteArray
&
base64
,
QByteArray::Base64Options
options
)
这是重载函数。
Returns a decoded copy of the Base64 array
base64
, using the options defined by
options
。若
options
包含
IgnoreBase64DecodingErrors
(the default), the input is not checked for validity; invalid characters in the input are skipped, enabling the decoding process to continue with subsequent characters. If
options
包含
AbortOnBase64DecodingErrors
, then decoding will stop at the first invalid character.
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 .
Returns the decoded data, or, if the
AbortOnBase64DecodingErrors
option was passed and the input data was invalid, an empty byte array.
注意： The fromBase64Encoding () function is recommended in new code.
该函数在 Qt 5.2 引入。
另请参阅 toBase64 () 和 fromBase64Encoding ().
[static]
QByteArray
QByteArray::
fromBase64
(const
QByteArray
&
base64
)
这是重载函数。
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 .
注意： The fromBase64Encoding () function is recommended in new code.
另请参阅 toBase64 () 和 fromBase64Encoding ().
[static]
QByteArray
QByteArray::
fromCFData
(
CFDataRef
data
)
构造新的 QByteArray containing a copy of the CFData data .
该函数在 Qt 5.3 引入。
另请参阅 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!"
另请参阅 toHex ().
[static]
QByteArray
QByteArray::
fromNSData
(const
NSData
*
data
)
构造新的 QByteArray containing a copy of the NSData data .
该函数在 Qt 5.3 引入。
另请参阅 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： 给定无效输入 (譬如：包含 %G5 序列的字符串，不是有效十六进制数字)，输出也将无效。例如：%G5 序列可以解码为 W。
该函数在 Qt 4.4 引入。
另请参阅 toPercentEncoding () 和 QUrl::fromPercentEncoding ().
[static]
QByteArray
QByteArray::
fromRawCFData
(
CFDataRef
data
)
构造 QByteArray that uses the bytes of the CFData data .
The data 的字节不拷贝。
The caller guarantees that the CFData will not be deleted or modified as long as this QByteArray object exists.
该函数在 Qt 5.3 引入。
另请参阅 fromCFData (), fromRawData (), toRawCFData ()，和 toCFData ().
[static]
QByteArray
QByteArray::
fromRawData
(const
char
*
data
,
int
size
)
构造 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 隐式共享 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 未拥有所有权对于 data , so the QByteArray destructor will never delete the raw data , even when the last QByteArray referring to data 被销毁。
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
'\0'-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.
另请参阅 setRawData (), data ()，和 constData ().
[static]
QByteArray
QByteArray::
fromRawNSData
(const
NSData
*
data
)
构造 QByteArray that uses the bytes of the NSData data .
The data 的字节不拷贝。
The caller guarantees that the NSData will not be deleted or modified as long as this QByteArray object exists.
该函数在 Qt 5.3 引入。
另请参阅 fromNSData (), fromRawData (), toRawNSData ()，和 toNSData ().
[static]
QByteArray
QByteArray::
fromStdString
(const
std::string
&
str
)
返回副本为 str string as a QByteArray .
该函数在 Qt 5.4 引入。
另请参阅 toStdString () 和 QString::fromStdString ().
Returns the first character in the byte array. Same as
at(0)
.
此函数为兼容 STL (标准模板库) 提供。
警告： 空字节数组调用此函数，会构成未定义行为。
该函数在 Qt 5.10 引入。
另请参阅 back (), at ()，和 operator[] ().
Returns a reference to the first character in the byte array. Same as
operator[](0)
.
此函数为兼容 STL (标准模板库) 提供。
警告： 空字节数组调用此函数，会构成未定义行为。
该函数在 Qt 5.10 引入。
另请参阅 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.
范例：
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
另请参阅 lastIndexOf (), contains ()，和 count ().
这是重载函数。
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.
范例：
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
另请参阅 lastIndexOf () 和 contains ().
这是重载函数。
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.
Inserts the byte array ba at index position i and returns a reference to this byte array.
范例：
QByteArray ba("Meal"); ba.insert(1, QByteArray("ontr")); // ba == "Montreal"
另请参阅 append (), prepend (), replace ()，和 remove ().
这是重载函数。
Inserts character ch at index position i in the byte array. If i 大于 size (), the array is first extended using resize ().
这是重载函数。
插入 count copies of character ch at index position i 在字节数组中。
若 i 大于 size (), the array is first extended using resize ().
该函数在 Qt 5.7 引入。
这是重载函数。
插入字符串 str 在位置 i 在字节数组中。
若 i 大于 size (), the array is first extended using resize ().
这是重载函数。
插入 len bytes of the string str 在位置 i 在字节数组中。
若 i 大于 size (), the array is first extended using resize ().
该函数在 Qt 4.6 引入。
返回
true
if the byte array has size 0; otherwise returns
false
.
范例：
QByteArray().isEmpty(); // returns true QByteArray("").isEmpty(); // returns true QByteArray("abc").isEmpty(); // returns false
另请参阅 size ().
返回
true
if this byte array contains only lowercase letters, otherwise returns
false
. The byte array is interpreted as a Latin-1 encoded string.
该函数在 Qt 5.12 引入。
返回
true
if this byte array is null; otherwise returns
false
.
范例：
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 ().
另请参阅 isEmpty ().
返回
true
if this byte array contains only uppercase letters, otherwise returns
false
. The byte array is interpreted as a Latin-1 encoded string.
该函数在 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.
范例：
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
另请参阅 indexOf (), contains ()，和 count ().
这是重载函数。
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.
范例：
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
另请参阅 indexOf () 和 contains ().
这是重载函数。
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.
返回的字节数组包含最左 len 字节对于此字节数组。
返回整个字节数组若 len 大于 size ().
范例：
QByteArray x("Pineapple"); QByteArray y = x.left(4); // y == "Pine"
另请参阅 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.
范例：
QByteArray x("apple"); QByteArray y = x.leftJustified(8, '.'); // y == "apple..."
另请参阅 rightJustified ().
如同 size ().
返回的字节数组包含 len 字节从此字节数组，起始于位置 pos .
若 len 为 -1 (默认)，或 pos + len >= size (), returns a byte array containing all bytes starting at position pos until the end of the byte array.
范例：
QByteArray x("Five pineapples"); QByteArray y = x.mid(5, 4); // y == "pine" QByteArray z = x.mid(5); // z == "pineapples"
另请参阅 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.
范例：
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)
这是重载函数。
另请参阅 toUInt ().
[static]
QByteArray
QByteArray::
number
(
qlonglong
n
,
int
base
= 10)
这是重载函数。
另请参阅 toLongLong ().
[static]
QByteArray
QByteArray::
number
(
qulonglong
n
,
int
base
= 10)
这是重载函数。
另请参阅 toULongLong ().
[static]
QByteArray
QByteArray::
number
(
double
n
,
char
f
= 'g',
int
prec
= 6)
这是重载函数。
Returns a byte array that contains the printed value of n , formatted in format f with precision prec .
自变量
n
is formatted according to the
f
format specified, which is
g
by default, and can be any of the following:
| 格式 | 含义 |
|---|---|
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.
另请参阅 toDouble ().
前置字节数组 ba 到此字节数组，并返回此字节数组的引用。
范例：
QByteArray x("ship"); QByteArray y("air"); x.prepend(y); // x == "airship"
这如同 insert(0, ba ).
注意： QByteArray 是 隐式共享 class. Consequently, if you prepend to an empty byte array, then the byte array will just share the data held in ba 。在这种情况下，不进行数据拷贝，花费 常量时间 。若共享实例被修改，它将被拷贝 (写时拷贝)，花费 线性时间 .
If the byte array being prepended to is not empty, a deep copy of the data is performed, taking 线性时间 .
这是重载函数。
前置字符 ch 到此字节数组。
这是重载函数。
前置 count copies of character ch 到此字节数组。
该函数在 Qt 5.7 引入。
这是重载函数。
前置字符串 str 到此字节数组。
这是重载函数。
前置 len bytes of the string str 到此字节数组。
该函数在 Qt 4.6 引入。
This function is provided for STL compatibility. It is equivalent to append( other ).
这是重载函数。
如同 append( ch ).
这是重载函数。
如同 append( str ).
This function is provided for STL compatibility. It is equivalent to prepend( other ).
这是重载函数。
如同 prepend( ch ).
这是重载函数。
如同 prepend( str ).
返回 STL-style reverse iterator pointing to the first character in the byte-array, in reverse order.
该函数在 Qt 5.6 引入。
另请参阅 begin (), crbegin ()，和 rend ().
这是重载函数。
该函数在 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 .
范例：
QByteArray ba("Montreal"); ba.remove(1, 4); // ba == "Meal"
返回 STL-style reverse iterator pointing to one past the last character in the byte-array, in reverse order.
该函数在 Qt 5.6 引入。
另请参阅 end (), crend ()，和 rbegin ().
这是重载函数。
该函数在 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.
范例：
QByteArray ba("ab"); ba.repeated(4); // returns "abababab"
该函数在 Qt 4.5 引入。
替换 len bytes from index position pos with the byte array after , and returns a reference to this byte array.
范例：
QByteArray x("Say yes!"); QByteArray y("no"); x.replace(4, 3, y); // x == "Say no!"
这是重载函数。
替换 len bytes from index position pos with the '\0'-terminated string after .
注意：这可以改变字节数组的长度。
这是重载函数。
替换 len bytes from index position pos with alen bytes from the string after . after is allowed to have '\0' characters.
该函数在 Qt 4.7 引入。
这是重载函数。
Replaces every occurrence of the character before 采用字符串 after .
这是重载函数。
Replaces every occurrence of the character before with the byte array after .
这是重载函数。
Replaces every occurrence of the string before 采用字符串 after .
这是重载函数。
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 '\0'-terminated.
这是重载函数。
Replaces every occurrence of the byte array before with the byte array after .
范例：
QByteArray ba("colour behaviour flavour neighbour"); ba.replace(QByteArray("ou"), QByteArray("o")); // ba == "color behavior flavor neighbor"
这是重载函数。
Replaces every occurrence of the byte array before 采用字符串 after .
这是重载函数。
Replaces every occurrence of the string before with the byte array after .
这是重载函数。
Replaces every occurrence of the character before with the character after .
试图分配内存为至少 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 ().
另请参阅 squeeze () 和 capacity ().
把字节数组的尺寸设为 size 字节。
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.
返回的字节数组包含最右 len 字节对于此字节数组。
返回整个字节数组若 len 大于 size ().
范例：
QByteArray x("Pineapple"); QByteArray y = x.right(5); // y == "apple"
另请参阅 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 .
范例：
QByteArray x("apple"); QByteArray y = x.rightJustified(8, '.'); // y == "...apple"
另请参阅 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.
范例：
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.
这是重载函数。
另请参阅 toShort ().
这是重载函数。
另请参阅 toUShort ().
这是重载函数。
另请参阅 toUInt ().
这是重载函数。
另请参阅 toLongLong ().
这是重载函数。
另请参阅 toULongLong ().
这是重载函数。
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.
另请参阅 toFloat ().
这是重载函数。
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 | 含义 |
|---|---|
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.
另请参阅 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.
该函数在 Qt 4.7 引入。
另请参阅 fromRawData (), data ()，和 constData ().
此函数为兼容 STL (标准模板库) 提供。它相当于 squeeze ().
该函数在 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()
函数返回
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 ' '.
范例：
QByteArray ba(" lots\t of\nwhitespace\r\n "); ba = ba.simplified(); // ba == "lots of whitespace";
另请参阅 trimmed ().
返回此字节数组的字节数。
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 automatically unless the 深拷贝 被创建。
范例：
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.
另请参阅 reserve () 和 capacity ().
返回
true
若此字节数组开头采用字节数组
ba
；否则返回
false
.
范例：
QByteArray url("ftp://ftp.qt-project.org/"); if (url.startsWith("ftp:")) ...
这是重载函数。
返回
true
if this byte array starts with character
ch
；否则返回
false
.
这是重载函数。
返回
true
if this byte array starts with string
str
；否则返回
false
.
交换字节数组 other with this byte array. This operation is very fast and never fails.
该函数在 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 .
另请参阅 fromBase64 ().
这是重载函数。
返回字节数组的副本，编码使用选项 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 .
该函数在 Qt 5.2 引入。
另请参阅 fromBase64 ().
创建 CFData 从 QByteArray . The caller owns the CFData object and is responsible for releasing it.
该函数在 Qt 5.3 引入。
另请参阅 toRawCFData (), fromCFData (), fromRawCFData ()，和 fromRawData ().
返回字节数组被转换成
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.
此函数忽略前导和结尾空格。
另请参阅 number ().
返回字节数组被转换成
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.
此函数忽略前导和结尾空格。
另请参阅 number ().
Returns a hex encoded copy of the byte array. The hex encoding uses the numbers 0-9 and the letters a-f.
另请参阅 fromHex ().
这是重载函数。
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.
范例：
QByteArray macAddress = QByteArray::fromHex("123456abcdef"); macAddress.toHex(':'); // returns "12:34:56:ab:cd:ef" macAddress.toHex(0); // returns "123456abcdef"
该函数在 Qt 5.9 引入。
另请参阅 fromHex ().
返回字节数组被转换成
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.
返回 0，若转换失败。
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.
另请参阅 number ().
返回字节数组被转换成
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.
返回 0，若转换失败。
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.
该函数在 Qt 4.1 引入。
另请参阅 number ().
返回字节数组被转换成
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.
返回 0，若转换失败。
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.
另请参阅 number ().
Returns a lowercase copy of the byte array. The bytearray is interpreted as a Latin-1 encoded string.
范例：
QByteArray x("Qt by THE QT COMPANY"); QByteArray y = x.toLower(); // y == "qt by the qt company"
另请参阅 isLower (), toUpper ()，和 8 位字符比较 .
创建 NSData 从 QByteArray . The NSData object is autoreleased.
该函数在 Qt 5.3 引入。
另请参阅 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.
范例：
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.
该函数在 Qt 4.4 引入。
另请参阅 fromPercentEncoding () 和 QUrl::toPercentEncoding ().
Constructs a CFData that uses the bytes of the QByteArray .
The QByteArray 的字节不拷贝。
The caller guarantees that the QByteArray will not be deleted or modified as long as this CFData object exists.
该函数在 Qt 5.3 引入。
另请参阅 toCFData (), fromRawCFData (), fromCFData ()，和 fromRawData ().
Constructs a NSData that uses the bytes of the QByteArray .
The QByteArray 的字节不拷贝。
The caller guarantees that the QByteArray will not be deleted or modified as long as this NSData object exists.
该函数在 Qt 5.3 引入。
另请参阅 fromRawNSData (), fromNSData (), fromRawData ()，和 toNSData ().
返回字节数组被转换成
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.
返回 0，若转换失败。
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.
另请参阅 number ().
返回 std::string 对象带有的数据包含在此 QByteArray .
此运算符主要用于传递 QByteArray 到接受 std::string 对象的函数。
该函数在 Qt 5.4 引入。
另请参阅 fromStdString () 和 QString::toStdString ().
返回字节数组被转换成
无符号 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.
返回 0，若转换失败。
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.
另请参阅 number ().
返回字节数组被转换成
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.
返回 0，若转换失败。
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.
该函数在 Qt 4.1 引入。
另请参阅 number ().
返回字节数组被转换成
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.
返回 0，若转换失败。
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.
另请参阅 number ().
返回字节数组被转换成
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.
返回 0，若转换失败。
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.
另请参阅 number ().
Returns an uppercase copy of the byte array. The bytearray is interpreted as a Latin-1 encoded string.
范例：
QByteArray x("Qt by THE QT COMPANY"); QByteArray y = x.toUpper(); // y == "QT BY THE QT COMPANY"
另请参阅 isUpper (), toLower ()，和 8 位字符比较 .
Returns a byte array that has whitespace removed from the start and the end.
Whitespace means any character for which the standard C++
isspace()
函数返回
true
in the C locale. This includes the ASCII characters '\t', '\n', '\v', '\f', '\r', and ' '.
范例：
QByteArray ba(" lots\t of\nwhitespace\r\n "); ba = ba.trimmed(); // ba == "lots\t of\nwhitespace";
不像 simplified ()，trimmed() 只留下内部空白。
另请参阅 simplified ().
截取字节数组按索引位置 pos .
若 pos 超越数组末尾，什么都不发生。
范例：
QByteArray ba("Stockholm"); ba.truncate(5); // ba == "Stock"
另请参阅 chop (), resize ()，和 left ().
返回
true
if this byte array is not equal to string
str
；否则返回
false
.
The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
比较是区分大小写的。
可以禁用此运算符通过定义
QT_NO_CAST_FROM_ASCII
当编译应用程序时。那么需要调用
QString::fromUtf8
(),
QString::fromLatin1
()，或
QString::fromLocal8Bit
() explicitly if you want to convert the byte array to a
QString
before doing the comparison.
追加字节数组 ba onto the end of this byte array and returns a reference to this byte array.
范例：
QByteArray x("free"); QByteArray y("dom"); x += y; // x == "freedom"
注意： QByteArray 是 隐式共享 类。因此，若追加到空字节数组，那么字节数组将仅仅共享的数据保持在 ba 。在这种情况下，不进行数据拷贝，花费 常量时间 。若共享实例被修改，它将被拷贝 (写时拷贝)，花费 线性时间 .
若要追加到的字节数组非空，履行数据深拷贝，花费 线性时间 .
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.
这是重载函数。
追加字符 ch onto the end of this byte array and returns a reference to this byte array.
这是重载函数。
追加字符串 str onto the end of this byte array and returns a reference to this byte array.
返回
true
if this byte array is lexically less than string
str
；否则返回
false
.
The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
比较是区分大小写的。
可以禁用此运算符通过定义
QT_NO_CAST_FROM_ASCII
当编译应用程序时。那么需要调用
QString::fromUtf8
(),
QString::fromLatin1
()，或
QString::fromLocal8Bit
() explicitly if you want to convert the byte array to a
QString
before doing the comparison.
返回
true
if this byte array is lexically less than or equal to string
str
；否则返回
false
.
The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
比较是区分大小写的。
可以禁用此运算符通过定义
QT_NO_CAST_FROM_ASCII
当编译应用程序时。那么需要调用
QString::fromUtf8
(),
QString::fromLatin1
()，或
QString::fromLocal8Bit
() explicitly if you want to convert the byte array to a
QString
before doing the comparison.
这是重载函数。
赋值 str 到此字节数组。
返回
true
if this byte array is equal to string
str
；否则返回
false
.
The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
比较是区分大小写的。
可以禁用此运算符通过定义
QT_NO_CAST_FROM_ASCII
当编译应用程序时。那么需要调用
QString::fromUtf8
(),
QString::fromLatin1
()，或
QString::fromLocal8Bit
() explicitly if you want to convert the byte array to a
QString
before doing the comparison.
返回
true
if this byte array is lexically greater than string
str
；否则返回
false
.
The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
比较是区分大小写的。
可以禁用此运算符通过定义
QT_NO_CAST_FROM_ASCII
当编译应用程序时。那么需要调用
QString::fromUtf8
(),
QString::fromLatin1
()，或
QString::fromLocal8Bit
() explicitly if you want to convert the byte array to a
QString
before doing the comparison.
返回
true
if this byte array is greater than or equal to string
str
；否则返回
false
.
The Unicode data is converted into 8-bit characters using QString::toUtf8 ().
比较是区分大小写的。
可以禁用此运算符通过定义
QT_NO_CAST_FROM_ASCII
当编译应用程序时。那么需要调用
QString::fromUtf8
(),
QString::fromLatin1
()，或
QString::fromLocal8Bit
() explicitly if you want to convert the byte array to a
QString
before doing the comparison.
返回字节按索引位置 i 作为可修改引用。
If an assignment is made beyond the end of the byte array, the array is extended with resize () before the assignment takes place.
范例：
QByteArray ba("Hello, world"); cout << ba[0]; // prints H ba[7] = 'W'; // ba == "Hello, World"
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.
注意： Before Qt 5.14 it was possible to use this operator to access a character at an out-of-bounds position in the byte array, and then assign to such a position, causing the byte array to be automatically resized. Furthermore, assigning a value to the returned QByteRef would cause a detach of the byte array, even if the byte array has been copied in the meanwhile (and the QByteRef kept alive while the copy was taken). These behaviors are deprecated, and will be changed in a future version of Qt.
另请参阅 at ().
这是重载函数。
如同 at( i ).
这是重载函数。
这是重载函数。
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.
该函数在 Qt 5.9 引入。
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.
另请参阅 qUncompress ().
这是重载函数。
Compresses the first nbytes of data at compression level compressionLevel and returns the compressed data in a new byte array.
Uncompresses the data byte array and returns a new byte array with the uncompressed data.
返回空 QByteArray 若输入数据被破坏。
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.
另请参阅 qCompress ().
这是重载函数。
Uncompresses the first nbytes of data and returns a new byte array with the uncompressed data.
可移植 snprintf() 函数，调用 qvsnprintf。
fmt
是
printf()
format string. The result is put into
str
, which is a buffer of at least
n
字节。
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.
另请参阅 qvsnprintf () 和 QString::asprintf ().
安全
strcmp()
函数。
比较 str1 and str2 。返回负值若 str1 小于 str2 , 0 if str1 等于 str2 或正值若 str1 大于 str2 .
特殊情况 1：返回 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).
另请参阅 qstrncmp (), qstricmp (), qstrnicmp (), 8 位字符比较 ，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.
另请参阅 qstrncpy ().
返回复制字符串。
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()
函数。
比较 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 小于 str2 , 0 if str1 等于 str2 或正值若 str1 大于 str2 .
特殊情况 1：返回 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).
另请参阅 qstrcmp (), qstrncmp (), qstrnicmp (), 8 位字符比较 ，和 QByteArray::compare ().
安全
strlen()
函数。
Returns the number of characters that precede the terminating '\0', or 0 if
str
is
nullptr
.
另请参阅 qstrnlen ().
安全
strncmp()
函数。
比较最多 len bytes of str1 and str2 .
Returns a negative value if str1 小于 str2 , 0 if str1 等于 str2 或正值若 str1 大于 str2 .
特殊情况 1：返回 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).
另请参阅 qstrcmp (), qstricmp (), qstrnicmp (), 8 位字符比较 ，和 QByteArray::compare ().
安全
strncpy()
函数。
拷贝最多
len
字节来自
src
(stopping at
len
or the terminating '\0' whichever comes first) into
dst
. Guarantees that
dst
is '\0'-terminated, except when
dst
is
nullptr
or
len
is 0. If
src
is
nullptr
，返回
nullptr
，否则返回
dst
.
This function assumes that dst is at least len characters long.
注意： 若 dst and src overlap, the behavior is undefined.
注意： Unlike strncpy(), this function does not write '\0' to all len bytes of dst , but stops after the terminating '\0'. In this sense, it's similar to C11's strncpy_s().
注意： When compiling with Visual C++ compiler version 14.00 (Visual C++ 2005) or later, internally the function strncpy_s will be used.
另请参阅 qstrcpy ().
安全
strnicmp()
函数。
比较最多 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 小于 str2 , 0 if str1 等于 str2 或正值若 str1 大于 str2 .
特殊情况 1：返回 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).
另请参阅 qstrcmp (), qstrncmp (), qstricmp (), 8 位字符比较 ，和 QByteArray::compare ().
安全
strnlen()
函数。
Returns the number of characters that precede the terminating '\0', but at most
maxlen
。若
str
is
nullptr
, returns 0.
该函数在 Qt 4.2 引入。
另请参阅 qstrlen ().
可移植
vsnprintf()
函数。会调用
::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
字节。
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。
另请参阅 qsnprintf () 和 QString::asprintf ().
这是重载函数。
返回
true
若字节数组
a1
不等于字节数组
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字节数组
a1
不等于字符串
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字符串
a1
不等于字节数组
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
返回的字节数组结果是串联字节数组 a1 和字节数组 a2 .
另请参阅 QByteArray::operator+= ().
这是重载函数。
返回的字节数组结果是串联字节数组 a1 and string a2 .
这是重载函数。
返回的字节数组结果是串联字节数组 a1 和字符 a2 .
这是重载函数。
返回的字节数组结果是串联字符串 a1 和字节数组 a2 .
这是重载函数。
返回的字节数组结果是串联字符 a1 和字节数组 a2 .
这是重载函数。
返回
true
若字节数组
a1
词汇上小于字节数组
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字节数组
a1
词法上小于字符串
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字符串
a1
词汇上小于字节数组
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
写入字节数组 ba 到流 out 并返回流引用。
另请参阅 序列化 Qt 数据类型 .
这是重载函数。
返回
true
若字节数组
a1
词法上 <= 字节数组
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字节数组
a1
词法上 <= 字符串
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字符串
a1
词法上 <= 字节数组
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字节数组
a1
等于字节数组
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字节数组
a1
等于字符串
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字符串
a1
等于字节数组
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字节数组
a1
词法上大于字节数组
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字节数组
a1
词法上大于字符串
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字符串
a1
词法上大于字节数组
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字节数组
a1
词法上大于等于字节数组
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字节数组
a1
词法上大于等于字符串
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
这是重载函数。
返回
true
若字符串
a1
词法上大于等于字节数组
a2
；否则返回
false
.
另请参阅 QByteArray::compare ().
读取字节数组到 ba 从流 in 并返回流引用。
另请参阅 序列化 Qt 数据类型 .
宏生成数据为 QByteArray 从字符串文字 ba 在编译时。创建 QByteArray 是自由的在此情况下，且生成的字节数组数据是存储在编译对象文件的只读段中。
例如：
QByteArray ba = QByteArrayLiteral("byte array contents");
使用 QByteArrayLiteral 而不是带双引号的纯 C++ 字符串文字可以显著加速创建 QByteArray 实例从编译时的已知数据。
另请参阅 QStringLiteral .
禁用自动转换从 QByteArray 到 const char * 或 const void *。
另请参阅 QT_NO_CAST_TO_ASCII and QT_NO_CAST_FROM_ASCII .