|
|
              
QByteArray Class ReferenceThe QByteArray class provides an array of bytes. More... #include <QByteArray>Inherited by: Q3CString. Note: All functions in this class are reentrant. Public Functions
Static Public Members
Related Non-Members
Macros
Detailed DescriptionThe QByteArray class provides an array of bytes. QByteArray can be used to store both raw bytes (including '\0's) and traditional 8-bit '\0'-terminated strings. Using QByteArray is much more convenient than using const char *. Behind the scenes, it always ensures that the data is followed by a '\0' terminator, and uses implicit sharing (copy-on-write) to reduce memory usage and avoid needless copying of data. In addition to QByteArray, Qt also provides the QString class to store string data. For most purposes, QString is the class you want to use. It stores 16-bit Unicode characters, making it easy to store non-ASCII/non-Latin-1 characters in your application. Furthermore, 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 * to its constructor. For example, the following code creates a byte array of size 5 containing the data "Hello": QByteArray ba("Hello"); Although the 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 deep copy to occur. To extract many bytes at a time, use left(), right(), or mid(). A QByteArray can embed '\0' bytes. The size() function always returns the size of the whole array, including embedded '\0' bytes. 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(). To obtain a pointer to the actual character data, call data() or 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(), and remove(). For example: 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() and 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() or 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. QByteArrays 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 All functions except 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(). Notes on LocaleNumber-String ConversionsFunctions 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. 8-bit Character ComparisonsIn 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>=(), toLower() and toUpper(). This issue does not apply to QStrings since they represent characters using Unicode. See also QString and QBitArray. Member Function Documentation
|
| Format | Meaning |
|---|---|
| e | format as [-]9.9e[+|-]999 |
| E | format as [-]9.9E[+|-]999 |
| f | format as [-]9.9 |
| g | use e or f format, whichever is the most concise |
| G | use E or f format, whichever is the most concise |
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
Note: The format of the number is not localized; the default C locale is used irrespective of the user's locale.
See also toDouble().
QByteArray & QByteArray::prepend ( const QByteArray & ba )
Prepends the byte array ba to this byte array and returns a reference to this byte array.
Example:
QByteArray x("ship"); QByteArray y("air"); x.prepend(y); // x == "airship"
This is the same as insert(0, ba).
Note: QByteArray is an implicitly shared class. Consequently, if this is an empty QByteArray, then this will just share the data held in ba. In this case, no copying of data is done, taking constant time. If a shared instance is modified, it will be copied (copy-on-write), taking linear time.
If this is not an empty QByteArray, a deep copy of the data is performed, taking linear time.
See also append() and insert().
QByteArray & QByteArray::prepend ( const char * str )
This is an overloaded function.
Prepends the string str to this byte array.
QByteArray & QByteArray::prepend ( const char * str, int len )
This is an overloaded function.
Prepends len bytes of the string str to this byte array.
This function was introduced in Qt 4.6.
QByteArray & QByteArray::prepend ( char ch )
This is an overloaded function.
Prepends the character ch to this byte array.
void QByteArray::push_back ( const QByteArray & other )
This function is provided for STL compatibility. It is equivalent to append(other).
void QByteArray::push_back ( const char * str )
This is an overloaded function.
Same as append(str).
void QByteArray::push_back ( char ch )
This is an overloaded function.
Same as append(ch).
void QByteArray::push_front ( const QByteArray & other )
This function is provided for STL compatibility. It is equivalent to prepend(other).
void QByteArray::push_front ( const char * str )
This is an overloaded function.
Same as prepend(str).
void QByteArray::push_front ( char ch )
This is an overloaded function.
Same as prepend(ch).
QByteArray & QByteArray::remove ( int pos, int len )
Removes len bytes from the array, starting at index position pos, and returns a reference to the array.
If 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.
Example:
QByteArray ba("Montreal"); ba.remove(1, 4); // ba == "Meal"
See also insert() and replace().
QByteArray QByteArray::repeated ( int times ) const
Returns a copy of this byte array repeated the specified number of times.
If times is less than 1, an empty byte array is returned.
Example:
QByteArray ba("ab"); ba.repeated(4); // returns "abababab"
This function was introduced in Qt 4.5.
QByteArray & QByteArray::replace ( int pos, int len, const QByteArray & after )
Replaces len bytes from index position pos with the byte array after, and returns a reference to this byte array.
Example:
QByteArray x("Say yes!"); QByteArray y("no"); x.replace(4, 3, y); // x == "Say no!"
See also insert() and remove().
QByteArray & QByteArray::replace ( int pos, int len, const char * after )
This is an overloaded function.
Replaces len bytes from index position pos with the zero terminated string after.
Notice: this can change the length of the byte array.
QByteArray & QByteArray::replace ( int pos, int len, const char * after, int alen )
This is an overloaded function.
Replaces len bytes from index position pos with alen bytes from the string after. after is allowed to have '\0' characters.
This function was introduced in Qt 4.7.
QByteArray & QByteArray::replace ( const QByteArray & before, const QByteArray & after )
This is an overloaded function.
Replaces every occurrence of the byte array before with the byte array after.
Example:
QByteArray ba("colour behaviour flavour neighbour"); ba.replace(QByteArray("ou"), QByteArray("o")); // ba == "color behavior flavor neighbor"
QByteArray & QByteArray::replace ( const char * before, const QByteArray & after )
This is an overloaded function.
Replaces every occurrence of the string before with the byte array after.
QByteArray & QByteArray::replace ( const char * before, int bsize, const char * after, int asize )
This is an overloaded function.
Replaces every occurrence of the string before with the string 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.
QByteArray & QByteArray::replace ( const QByteArray & before, const char * after )
This is an overloaded function.
Replaces every occurrence of the byte array before with the string after.
QByteArray & QByteArray::replace ( const QString & before, const QByteArray & after )
This is an overloaded function.
Replaces every occurrence of the string before with the byte array after. The Unicode data is converted into 8-bit characters using QString::toAscii().
If the QString contains non-ASCII Unicode characters, using this function can lead to loss of information. You can disable this function by defining QT_NO_CAST_TO_ASCII when you compile your applications. You then need to call QString::toAscii() (or QString::toLatin1() or QString::toUtf8() or QString::toLocal8Bit()) explicitly if you want to convert the data to const char *.
QByteArray & QByteArray::replace ( const QString & before, const char * after )
This is an overloaded function.
Replaces every occurrence of the string before with the string after.
QByteArray & QByteArray::replace ( const char * before, const char * after )
This is an overloaded function.
Replaces every occurrence of the string before with the string after.
QByteArray & QByteArray::replace ( char before, const QByteArray & after )
This is an overloaded function.
Replaces every occurrence of the character before with the byte array after.
QByteArray & QByteArray::replace ( char before, const QString & after )
This is an overloaded function.
Replaces every occurrence of the character before with the string after. The Unicode data is converted into 8-bit characters using QString::toAscii().
If the QString contains non-ASCII Unicode characters, using this function can lead to loss of information. You can disable this function by defining QT_NO_CAST_TO_ASCII when you compile your applications. You then need to call QString::toAscii() (or QString::toLatin1() or QString::toUtf8() or QString::toLocal8Bit()) explicitly if you want to convert the data to const char *.
QByteArray & QByteArray::replace ( char before, const char * after )
This is an overloaded function.
Replaces every occurrence of the character before with the string after.
QByteArray & QByteArray::replace ( char before, char after )
This is an overloaded function.
Replaces every occurrence of the character before with the character after.
void QByteArray::reserve ( int size )
Attempts to allocate memory for at least 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().
See also squeeze() and capacity().
void QByteArray::resize ( int size )
Sets the size of the byte array to size bytes.
If 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.
If size is less than the current size, bytes are removed from the end.
See also size() and truncate().
QByteArray QByteArray::right ( int len ) const
Returns a byte array that contains the rightmost len bytes of this byte array.
The entire byte array is returned if len is greater than size().
Example:
QByteArray x("Pineapple"); QByteArray y = x.right(5); // y == "apple"
See also endsWith(), left(), and mid().
QByteArray QByteArray::rightJustified ( int width, char fill = ' ', bool truncate = false ) const
Returns a byte array of size width that contains the fill character followed by this byte array.
If 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.
If truncate is true and the size of the byte array is more than width, then the resulting byte array is truncated at position width.
Example:
QByteArray x("apple"); QByteArray y = x.rightJustified(8, '.'); // y == "...apple"
See also leftJustified().
QByteArray & QByteArray::setNum ( int n, int base = 10 )
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.
Example:
QByteArray ba; int n = 63; ba.setNum(n); // ba == "63" ba.setNum(n, 16); // ba == "3f"
Note: The format of the number is not localized; the default C locale is used irrespective of the user's locale.
See also number() and toInt().
QByteArray & QByteArray::setNum ( uint n, int base = 10 )
This is an overloaded function.
See also toUInt().
QByteArray & QByteArray::setNum ( short n, int base = 10 )
This is an overloaded function.
See also toShort().
QByteArray & QByteArray::setNum ( ushort n, int base = 10 )
This is an overloaded function.
See also toUShort().
QByteArray & QByteArray::setNum ( qlonglong n, int base = 10 )
This is an overloaded function.
See also toLongLong().
QByteArray & QByteArray::setNum ( qulonglong n, int base = 10 )
This is an overloaded function.
See also toULongLong().
QByteArray & QByteArray::setNum ( double n, char f = 'g', int prec = 6 )
This is an overloaded function.
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.
The format f can be any of the following:
| Format | Meaning |
|---|---|
| e | format as [-]9.9e[+|-]999 |
| E | format as [-]9.9E[+|-]999 |
| f | format as [-]9.9 |
| g | use e or f format, whichever is the most concise |
| G | use E or f format, whichever is the most concise |
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).
Note: The format of the number is not localized; the default C locale is used irrespective of the user's locale.
See also toDouble().
QByteArray & QByteArray::setNum ( float n, char f = 'g', int prec = 6 )
This is an overloaded function.
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.
Note: The format of the number is not localized; the default C locale is used irrespective of the user's locale.
See also toFloat().
QByteArray & QByteArray::setRawData ( const char * data, uint size )
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 existings QByteArray objects to save memory re-allocations.
This function was introduced in Qt 4.7.
See also fromRawData(), data(), and constData().
QByteArray QByteArray::simplified () const
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() function returns true. This includes the ASCII characters '\t', '\n', '\v', '\f', '\r', and ' '.
Example:
QByteArray ba(" lots\t of\nwhitespace\r\n "); ba = ba.simplified(); // ba == "lots of whitespace";
See also trimmed().
int QByteArray::size () const
Returns the number of bytes in this byte array.
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() and 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 deep copy is created.
Example:
QByteArray ba("Hello"); int n = ba.size(); // n == 5 ba.data()[0]; // returns 'H' ba.data()[4]; // returns 'o' ba.data()[5]; // returns '\0'
See also isEmpty() and resize().
QList<QByteArray> QByteArray::split ( char sep ) const
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.
void QByteArray::squeeze ()
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.
See also reserve() and capacity().
bool QByteArray::startsWith ( const QByteArray & ba ) const
Returns true if this byte array starts with byte array ba; otherwise returns false.
Example:
QByteArray url("ftp://ftp.qt.nokia.com/"); if (url.startsWith("ftp:")) ...
See also endsWith() and left().
bool QByteArray::startsWith ( const char * str ) const
This is an overloaded function.
Returns true if this byte array starts with string str; otherwise returns false.
bool QByteArray::startsWith ( char ch ) const
This is an overloaded function.
Returns true if this byte array starts with character ch; otherwise returns false.
void QByteArray::swap ( QByteArray & other )
Swaps byte array other with this byte array. This operation is very fast and never fails.
This function was introduced in Qt 4.8.
QByteArray QByteArray::toBase64 () const
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 2045.
See also fromBase64().
double QByteArray::toDouble ( bool * ok = 0 ) const
Returns the byte array converted to a double value.
Returns 0.0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
QByteArray string("1234.56"); double a = string.toDouble(); // a == 1234.56
Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.
See also number().
float QByteArray::toFloat ( bool * ok = 0 ) const
Returns the byte array converted to a float value.
Returns 0.0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.
See also number().
QByteArray QByteArray::toHex () const
Returns a hex encoded copy of the byte array. The hex encoding uses the numbers 0-9 and the letters a-f.
See also fromHex().
int QByteArray::toInt ( bool * ok = 0, int base = 10 ) const
Returns the byte array converted to an int using base base, which is 10 by default and must be between 2 and 36, or 0.
If 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.
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set 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
Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.
See also number().
long QByteArray::toLong ( bool * ok = 0, int base = 10 ) const
Returns the byte array converted to a long int using base base, which is 10 by default and must be between 2 and 36, or 0.
If 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.
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set 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
Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.
This function was introduced in Qt 4.1.
See also number().
qlonglong QByteArray::toLongLong ( bool * ok = 0, int base = 10 ) const
Returns the byte array converted to a long long using base base, which is 10 by default and must be between 2 and 36, or 0.
If 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.
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.
See also number().
QByteArray QByteArray::toLower () const
Returns a lowercase copy of the byte array. The bytearray is interpreted as a Latin-1 encoded string.
Example:
QByteArray x("Qt by NOKIA"); QByteArray y = x.toLower(); // y == "qt by nokia"
See also toUpper() and 8-bit Character Comparisons.
QByteArray QByteArray::toPercentEncoding ( const QByteArray & exclude = QByteArray(), const QByteArray & include = QByteArray(), char percent = '%' ) const
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 include. The percent character is always encoded.
Example:
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.
This function was introduced in Qt 4.4.
See also fromPercentEncoding() and QUrl::toPercentEncoding().
short QByteArray::toShort ( bool * ok = 0, int base = 10 ) const
Returns the byte array converted to a short using base base, which is 10 by default and must be between 2 and 36, or 0.
If 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.
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.
See also number().
uint QByteArray::toUInt ( bool * ok = 0, int base = 10 ) const
Returns the byte array converted to an unsigned int using base base, which is 10 by default and must be between 2 and 36, or 0.
If 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.
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.
See also number().
ulong QByteArray::toULong ( bool * ok = 0, int base = 10 ) const
Returns the byte array converted to an unsigned long int using base base, which is 10 by default and must be between 2 and 36, or 0.
If 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.
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.
This function was introduced in Qt 4.1.
See also number().
qulonglong QByteArray::toULongLong ( bool * ok = 0, int base = 10 ) const
Returns the byte array converted to an unsigned long long using base base, which is 10 by default and must be between 2 and 36, or 0.
If 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.
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.
See also number().
ushort QByteArray::toUShort ( bool * ok = 0, int base = 10 ) const
Returns the byte array converted to an unsigned short using base base, which is 10 by default and must be between 2 and 36, or 0.
If 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.
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.
See also number().
QByteArray QByteArray::toUpper () const
Returns an uppercase copy of the byte array. The bytearray is interpreted as a Latin-1 encoded string.
Example:
QByteArray x("Qt by NOKIA"); QByteArray y = x.toUpper(); // y == "QT BY NOKIA"
See also toLower() and 8-bit Character Comparisons.
QByteArray QByteArray::trimmed () const
Returns a byte array that has whitespace removed from the start and the end.
Whitespace means any character for which the standard C++ isspace() function returns true. This includes the ASCII characters '\t', '\n', '\v', '\f', '\r', and ' '.
Example:
QByteArray ba(" lots\t of\nwhitespace\r\n "); ba = ba.trimmed(); // ba == "lots\t of\nwhitespace";
Unlike simplified(), trimmed() leaves internal whitespace alone.
See also simplified().
void QByteArray::truncate ( int pos )
Truncates the byte array at index position pos.
If pos is beyond the end of the array, nothing happens.
Example:
QByteArray ba("Stockholm"); ba.truncate(5); // ba == "Stock"
See also chop(), resize(), and left().
QByteArray::operator const char * () const
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. The pointer remains valid as long as the array isn't reallocated or destroyed.
This operator is mostly useful to pass a byte array to a function that accepts a const char *.
You can disable this operator by defining QT_NO_CAST_FROM_BYTEARRAY when you compile your applications.
Note: A QByteArray can store any byte values including '\0's, but most functions that take char * arguments assume that the data ends at the first '\0' they encounter.
See also constData().
QByteArray::operator const void * () const
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. The pointer remains valid as long as the array isn't reallocated or destroyed.
This operator is mostly useful to pass a byte array to a function that accepts a const char *.
You can disable this operator by defining QT_NO_CAST_FROM_BYTEARRAY when you compile your applications.
Note: A QByteArray can store any byte values including '\0's, but most functions that take char * arguments assume that the data ends at the first '\0' they encounter.
See also constData().
bool QByteArray::operator!= ( const QString & str ) const
Returns true if this byte array is not equal to string str; otherwise returns false.
The Unicode data is converted into 8-bit characters using QString::toAscii().
The comparison is case sensitive.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. You then need to call QString::fromAscii(), QString::fromLatin1(), QString::fromUtf8(), or QString::fromLocal8Bit() explicitly if you want to convert the byte array to a QString before doing the comparison.
QByteArray & QByteArray::operator+= ( const QByteArray & ba )
Appends the byte array ba onto the end of this byte array and returns a reference to this byte array.
Example:
QByteArray x("free"); QByteArray y("dom"); x += y; // x == "freedom"
Note: QByteArray is an implicitly shared class. Consequently, if this is an empty QByteArray, then this will just share the data held in ba. In this case, no copying of data is done, taking constant time. If a shared instance is modified, it will be copied (copy-on-write), taking linear time.
If this is not an empty QByteArray, a deep copy of the data is performed, taking linear time.
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.
See also append() and prepend().
QByteArray & QByteArray::operator+= ( const QString & str )
This is an overloaded function.
Appends the string 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::toAscii().
If the QString contains non-ASCII Unicode characters, using this operator can lead to loss of information. You can disable this operator by defining QT_NO_CAST_TO_ASCII when you compile your applications. You then need to call QString::toAscii() (or QString::toLatin1() or QString::toUtf8() or QString::toLocal8Bit()) explicitly if you want to convert the data to const char *.
QByteArray & QByteArray::operator+= ( const char * str )
This is an overloaded function.
Appends the string str onto the end of this byte array and returns a reference to this byte array.
QByteArray & QByteArray::operator+= ( char ch )
This is an overloaded function.
Appends the character ch onto the end of this byte array and returns a reference to this byte array.
bool QByteArray::operator< ( const QString & str ) const
Returns true if this byte array is lexically less than string str; otherwise returns false.
The Unicode data is converted into 8-bit characters using QString::toAscii().
The comparison is case sensitive.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. You then need to call QString::fromAscii(), QString::fromLatin1(), QString::fromUtf8(), or QString::fromLocal8Bit() explicitly if you want to convert the byte array to a QString before doing the comparison.
bool QByteArray::operator<= ( const QString & str ) const
Returns true if this byte array is lexically less than or equal to string str; otherwise returns false.
The Unicode data is converted into 8-bit characters using QString::toAscii().
The comparison is case sensitive.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. You then need to call QString::fromAscii(), QString::fromLatin1(), QString::fromUtf8(), or QString::fromLocal8Bit() explicitly if you want to convert the byte array to a QString before doing the comparison.
QByteArray & QByteArray::operator= ( const QByteArray & other )
Assigns other to this byte array and returns a reference to this byte array.
QByteArray & QByteArray::operator= ( const char * str )
This is an overloaded function.
Assigns str to this byte array.
bool QByteArray::operator== ( const QString & str ) const
Returns true if this byte array is equal to string str; otherwise returns false.
The Unicode data is converted into 8-bit characters using QString::toAscii().
The comparison is case sensitive.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. You then need to call QString::fromAscii(), QString::fromLatin1(), QString::fromUtf8(), or QString::fromLocal8Bit() explicitly if you want to convert the byte array to a QString before doing the comparison.
bool QByteArray::operator> ( const QString & str ) const
Returns true if this byte array is lexically greater than string str; otherwise returns false.
The Unicode data is converted into 8-bit characters using QString::toAscii().
The comparison is case sensitive.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. You then need to call QString::fromAscii(), QString::fromLatin1(), QString::fromUtf8(), or QString::fromLocal8Bit() explicitly if you want to convert the byte array to a QString before doing the comparison.
bool QByteArray::operator>= ( const QString & str ) const
Returns true if this byte array is greater than or equal to string str; otherwise returns false.
The Unicode data is converted into 8-bit characters using QString::toAscii().
The comparison is case sensitive.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. You then need to call QString::fromAscii(), QString::fromLatin1(), QString::fromUtf8(), or QString::fromLocal8Bit() explicitly if you want to convert the byte array to a QString before doing the comparison.
QByteRef QByteArray::operator[] ( int i )
Returns the byte at index position i as a modifiable reference.
If an assignment is made beyond the end of the byte array, the array is extended with resize() before the assignment takes place.
Example:
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.
See also at().
char QByteArray::operator[] ( int i ) const
This is an overloaded function.
Same as at(i).
QByteRef QByteArray::operator[] ( uint i )
This is an overloaded function.
char QByteArray::operator[] ( uint i ) const
This is an overloaded function.
Related Non-Members
quint16 qChecksum ( const char * data, uint len )
Returns the CRC-16 checksum of the first len bytes of data.
The checksum is independent of the byte order (endianness).
Note: This function is a 16-bit cache conserving (16 entry table) implementation of the CRC-16-CCITT algorithm.
QByteArray qCompress ( const QByteArray & data, int compressionLevel = -1 )
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.
See also qUncompress().
QByteArray qCompress ( const uchar * data, int nbytes, int compressionLevel = -1 )
This is an overloaded function.
Compresses the first nbytes of data and returns the compressed data in a new byte array.
QByteArray qUncompress ( const QByteArray & data )
Uncompresses the data byte array and returns a new byte array with the uncompressed data.
Returns an empty QByteArray if the input data was corrupt.
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.
Note: 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.
See also qCompress().
QByteArray qUncompress ( const uchar * data, int nbytes )
This is an overloaded function.
Uncompresses the first nbytes of data and returns a new byte array with the uncompressed data.
int qsnprintf ( char * str, size_t n, const char * fmt, ... )
A portable snprintf() function, calls qvsnprintf.
fmt is the printf() format string. The result is put into str, which is a buffer of at least n bytes.
Warning: Call this function only when you know what you are doing since it shows different behavior on certain platforms. Use QString::sprintf() to format a string instead.
See also qvsnprintf() and QString::sprintf().
int qstrcmp ( const char * str1, const char * str2 )
A safe strcmp() function.
Compares str1 and str2. Returns a negative value if str1 is less than str2, 0 if str1 is equal to str2 or a positive value if str1 is greater than str2.
Special case 1: Returns 0 if str1 and str2 are both 0.
Special case 2: Returns an arbitrary non-zero value if str1 is 0 or str2 is 0 (but not both).
See also qstrncmp(), qstricmp(), qstrnicmp(), and 8-bit Character Comparisons.
char * qstrcpy ( char * dst, const char * src )
Copies all the characters up to and including the '\0' from src into dst and returns a pointer to dst. If src is 0, it immediately returns 0.
This function assumes that dst is large enough to hold the contents of src.
See also qstrncpy().
char * qstrdup ( const char * src )
Returns a duplicate string.
Allocates space for a copy of src, copies it, and returns a pointer to the copy. If src is 0, it immediately returns 0.
Ownership is passed to the caller, so the returned string must be deleted using delete[].
int qstricmp ( const char * str1, const char * str2 )
A safe stricmp() function.
Compares 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 is less than str2, 0 if str1 is equal to str2 or a positive value if str1 is greater than str2.
Special case 1: Returns 0 if str1 and str2 are both 0.
Special case 2: Returns a random non-zero value if str1 is 0 or str2 is 0 (but not both).
See also qstrcmp(), qstrncmp(), qstrnicmp(), and 8-bit Character Comparisons.
uint qstrlen ( const char * str )
A safe strlen() function.
Returns the number of characters that precede the terminating '\0', or 0 if str is 0.
See also qstrnlen().
int qstrncmp ( const char * str1, const char * str2, uint len )
A safe strncmp() function.
Compares at most len bytes of str1 and str2.
Returns a negative value if str1 is less than str2, 0 if str1 is equal to str2 or a positive value if str1 is greater than str2.
Special case 1: Returns 0 if str1 and str2 are both 0.
Special case 2: Returns a random non-zero value if str1 is 0 or str2 is 0 (but not both).
See also qstrcmp(), qstricmp(), qstrnicmp(), and 8-bit Character Comparisons.
char * qstrncpy ( char * dst, const char * src, uint len )
A safe strncpy() function.
Copies at most len bytes from 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 0, returns 0 immediately.
This function assumes that dst is at least len characters long.
Note: When compiling with Visual C++ compiler version 14.00 (Visual C++ 2005) or later, internally the function strncpy_s will be used.
See also qstrcpy().
int qstrnicmp ( const char * str1, const char * str2, uint len )
A safe strnicmp() function.
Compares at most 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 is less than str2, 0 if str1 is equal to str2 or a positive value if str1 is greater than str2.
Special case 1: Returns 0 if str1 and str2 are both 0.
Special case 2: Returns a random non-zero value if str1 is 0 or str2 is 0 (but not both).
See also qstrcmp(), qstrncmp(), qstricmp(), and 8-bit Character Comparisons.
uint qstrnlen ( const char * str, uint maxlen )
A safe strnlen() function.
Returns the number of characters that precede the terminating '\0', but at most maxlen. If str is 0, returns 0.
This function was introduced in Qt 4.2.
See also qstrlen().
int qvsnprintf ( char * str, size_t n, const char * fmt, va_list ap )
A portable vsnprintf() function. Will call ::vsnprintf(), ::_vsnprintf(), or ::vsnprintf_s depending on the system, or fall back to an internal version.
fmt is the printf() format string. The result is put into str, which is a buffer of at least n bytes.
The caller is responsible to call va_end() on ap.
Warning: 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::sprintf() instead.
See also qsnprintf() and QString::sprintf().
bool operator!= ( const QByteArray & a1, const QByteArray & a2 )
This is an overloaded function.
Returns true if byte array a1 is not equal to byte array a2; otherwise returns false.
bool operator!= ( const QByteArray & a1, const char * a2 )
This is an overloaded function.
Returns true if byte array a1 is not equal to string a2; otherwise returns false.
bool operator!= ( const char * a1, const QByteArray & a2 )
This is an overloaded function.
Returns true if string a1 is not equal to byte array a2; otherwise returns false.
const QByteArray operator+ ( const QByteArray & a1, const char * a2 )
This is an overloaded function.
Returns a byte array that is the result of concatenating byte array a1 and string a2.
const QByteArray operator+ ( const QByteArray & a1, char a2 )
This is an overloaded function.
Returns a byte array that is the result of concatenating byte array a1 and character a2.
const QByteArray operator+ ( const char * a1, const QByteArray & a2 )
This is an overloaded function.
Returns a byte array that is the result of concatenating string a1 and byte array a2.
const QByteArray operator+ ( char a1, const QByteArray & a2 )
This is an overloaded function.
Returns a byte array that is the result of concatenating character a1 and byte array a2.
const QByteArray operator+ ( const QByteArray & a1, const QByteArray & a2 )
Returns a byte array that is the result of concatenating byte array a1 and byte array a2.
See also QByteArray::operator+=().
bool operator< ( const QByteArray & a1, const QByteArray & a2 )
This is an overloaded function.
Returns true if byte array a1 is lexically less than byte array a2; otherwise returns false.
bool operator< ( const QByteArray & a1, const char * a2 )
This is an overloaded function.
Returns true if byte array a1 is lexically less than string a2; otherwise returns false.
bool operator< ( const char * a1, const QByteArray & a2 )
This is an overloaded function.
Returns true if string a1 is lexically less than byte array a2; otherwise returns false.
QDataStream & operator<< ( QDataStream & out, const QByteArray & ba )
Writes byte array ba to the stream out and returns a reference to the stream.
See also Serializing Qt Data Types.
bool operator<= ( const QByteArray & a1, const QByteArray & a2 )
This is an overloaded function.
Returns true if byte array a1 is lexically less than or equal to byte array a2; otherwise returns false.
bool operator<= ( const QByteArray & a1, const char * a2 )
This is an overloaded function.
Returns true if byte array a1 is lexically less than or equal to string a2; otherwise returns false.
bool operator<= ( const char * a1, const QByteArray & a2 )
This is an overloaded function.
Returns true if string a1 is lexically less than or equal to byte array a2; otherwise returns false.
bool operator== ( const QByteArray & a1, const QByteArray & a2 )
This is an overloaded function.
Returns true if byte array a1 is equal to byte array a2; otherwise returns false.
bool operator== ( const QByteArray & a1, const char * a2 )
This is an overloaded function.
Returns true if byte array a1 is equal to string a2; otherwise returns false.
bool operator== ( const char * a1, const QByteArray & a2 )
This is an overloaded function.
Returns true if string a1 is equal to byte array a2; otherwise returns false.
bool operator> ( const QByteArray & a1, const QByteArray & a2 )
This is an overloaded function.
Returns true if byte array a1 is lexically greater than byte array a2; otherwise returns false.
bool operator> ( const QByteArray & a1, const char * a2 )
This is an overloaded function.
Returns true if byte array a1 is lexically greater than string a2; otherwise returns false.
bool operator> ( const char * a1, const QByteArray & a2 )
This is an overloaded function.
Returns true if string a1 is lexically greater than byte array a2; otherwise returns false.
bool operator>= ( const QByteArray & a1, const QByteArray & a2 )
This is an overloaded function.
Returns true if byte array a1 is lexically greater than or equal to byte array a2; otherwise returns false.
bool operator>= ( const QByteArray & a1, const char * a2 )
This is an overloaded function.
Returns true if byte array a1 is lexically greater than or equal to string a2; otherwise returns false.
bool operator>= ( const char * a1, const QByteArray & a2 )
This is an overloaded function.
Returns true if string a1 is lexically greater than or equal to byte array a2; otherwise returns false.
QDataStream & operator>> ( QDataStream & in, QByteArray & ba )
Reads a byte array into ba from the stream in and returns a reference to the stream.
See also Serializing Qt Data Types.
Macro Documentation
QT_NO_CAST_FROM_BYTEARRAY
Disables automatic conversions from QByteArray to const char * or const void *.
See also QT_NO_CAST_TO_ASCII and QT_NO_CAST_FROM_ASCII.
|
|
Best Of
Actualités les plus lues
- Pourquoi les programmeurs sont-ils moins payés que les gestionnaires de programmes ? Manquent-ils de pouvoir de négociation ? 42
- Qt Commercial : Digia organise un webinar gratuit le 27 mars sur la conception d'interfaces utilisateur et d'applications avec le framework 0
- Interfaces mobiles : nouveaux usages, nouvelles ergonomies, par Miratech 0
- Implémentation d'une table de hachage à référence faible avec Qt, un article de Christophe Dumez traduit par Thibaut Cuvelier 1
- « Quelque chose ne va vraiment pas avec les développeurs "modernes" », un développeur à "l'ancienne" critique la multiplication des bibliothèques 94
- Apercevoir la troisième dimension ou l'utilisation multithreadée d'OpenGL dans Qt, un article des Qt Quarterly traduit par Guillaume Belz 0
- Les développeurs ignorent-ils trop les failles découvertes dans leur code ? Prenez-vous en compte les remarques des autres ? 17
- Pourquoi les programmeurs sont-ils moins payés que les gestionnaires de programmes ? Manquent-ils de pouvoir de négociation ? 42
- Quelles nouveautés de C++11 Visual C++ doit-il rapidement intégrer ? Donnez-nous votre avis 10
- Adieu qmake, bienvenue qbs : Qt Building Suite, un outil déclaratif et extensible pour la compilation de projets Qt 17
- 2017 : un quinquennat pour une nouvelle version du C++ ? Possible, selon Herb Sutter 6
- Linus Torvalds : le "C++ est un langage horrible", en justifiant le choix du C pour le système de gestion de version Git 100
- Comment prendre en compte l'utilisateur dans vos applications ? Pour un développeur, « 90 % des utilisateurs sont des idiots » 229
- Quel est LE livre que tout développeur doit lire absolument ? Celui qui vous a le plus marqué et inspiré 96
- Apple cède et s'engage à payer des droits à Nokia, le conflit des brevets entre les deux firmes s'achève 158
- Nokia porte à nouveau plainte contre Apple pour violation de sept nouveaux brevets 158
- Quel est le code dont vous êtes le plus fier ? Pourquoi l'avez-vous écrit ? Et pourquoi vous a-t-il donné autant de satisfaction ? 83
- Le Draft final de la norme C++ 0X validé 181
Le Qt Labs au hasard
Le moteur de rendu OpenGL
Communauté
Ressources
- 91 cours et tutoriels Qt
- F.A.Q. Qt : 200 questions et réponses
- 48 Qt Quarterly, 35 Qt Labs et 22 Qt DevNet en français
- 43 outils Qt
- 99 sources Qt
- 26 binaires Qt
- 6 livres Qt et 9 critiques
- La documentation de Qt 4.7 en français : 157 classes, 70 concepts et 24 modules
- 3 certifications Qt
Liens utiles
Contact
- Vous souhaitez rejoindre la rédaction ou proposer un tutoriel, une traduction, une question... ? Postez dans le forum Contribuez ou contactez-nous par MP ou par email (voir en bas de page).
Qt dans le magazine
| Cette page est une traduction d'une page de la documentation de Qt, écrite par Nokia Corporation and/or its subsidiary(-ies). Les éventuels problèmes résultant d'une mauvaise traduction ne sont pas imputables à Nokia. | Qt 4.8 | |
| Copyright © 2012 Developpez LLC. Tous droits réservés Developpez LLC. Aucune reproduction, même partielle, ne peut être faite de ce site et de l'ensemble de son contenu : textes, documents et images sans l'autorisation expresse de Developpez LLC. Sinon, vous encourez selon la loi jusqu'à 3 ans de prison et jusqu'à 300 000 E de dommages et intérêts. Cette page est déposée à la SACD. | ||
| Vous avez déniché une erreur ? Un bug ? Une redirection cassée ? Ou tout autre problème, quel qu'il soit ? Ou bien vous désirez participer à ce projet de traduction ? N'hésitez pas à nous contacter ou par MP ! | ||
Copyright © 2000-2012 - www.developpez.com