QByteArray Class Reference
^{[QtCore module]}

Note on 8-bit Character Comparisons

In 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

QByteArray::QByteArray ()

Constructs an empty byte array.

See also isEmpty().

QByteArray::QByteArray ( const char * str )

Constructs a byte array initialized with the string str.

QByteArray makes a deep copy of the string data.

QByteArray::QByteArray ( const char * data, int size )

Constructs a byte array containing the first size bytes of array data.

If data is 0, a null byte array is constructed.

QByteArray makes a deep copy of the string data.

See also fromRawData().

QByteArray::QByteArray ( int size, char ch )

Constructs a byte array of size size with every byte set to character ch.

See also fill().

QByteArray::QByteArray ( const QByteArray & other )

Constructs a copy of other.

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

See also operator=().

QByteArray::~QByteArray ()

Destroys the byte array.

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

Appends the byte array ba onto the end of this byte array.

Example:

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

This is the same as insert(size(), ba).

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

See also operator+=(), prepend(), and insert().

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

This is an overloaded member function, provided for convenience.

Appends the string str 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 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::append ( const char * str )

This is an overloaded member function, provided for convenience.

Appends the string str to this byte array.

QByteArray & QByteArray::append ( char ch )

This is an overloaded member function, provided for convenience.

Appends the character ch to this byte array.

const char QByteArray::at ( int i ) const

Returns the character at index position i in the byte array.

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

See also operator[]().

int QByteArray::capacity () const

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().

See also reserve() and squeeze().

void QByteArray::chop ( int n )

Removes n bytes from the end of the byte array.

If n is greater than size(), the result is an empty byte array.

Example:

    QByteArray ba("STARTTLS\r\n");
    ba.chop(2);                 // ba == "STARTTLS"

See also truncate(), resize(), and left().

void QByteArray::clear ()

Clears the contents of the byte array and makes it empty.

See also resize() and isEmpty().

const char * QByteArray::constData () 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 byte array isn't reallocated.

This function is mostly useful to pass a byte array to a function that accepts a const char *.

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 data() and operator[]().

bool QByteArray::contains ( const QByteArray & ba ) const

Returns true if the byte array contains an occurrence of the byte array ba; otherwise returns false.

See also indexOf() and count().

bool QByteArray::contains ( const char * str ) const

This is an overloaded member function, provided for convenience.

Returns true if the byte array contains the string str; otherwise returns false.

bool QByteArray::contains ( char ch ) const

This is an overloaded member function, provided for convenience.

Returns true if the byte array contains the character ch; otherwise returns false.

int QByteArray::count ( const QByteArray & ba ) const

Returns the number of (potentially overlapping) occurrences of byte array ba in this byte array.

See also contains() and indexOf().

int QByteArray::count ( const char * str ) const

This is an overloaded member function, provided for convenience.

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

int QByteArray::count ( char ch ) const

This is an overloaded member function, provided for convenience.

Returns the number of occurrences of character ch in the byte array.

See also contains() and indexOf().

int QByteArray::count () const

This is an overloaded member function, provided for convenience.

Same as size().

char * QByteArray::data ()

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.

Example:

    QByteArray ba("Hello world");
    char *data = ba.data();
    while (*data) {
        cout << "[" << *data << "]" << endl;
        ++data;
    }

The pointer remains valid as long as the byte array isn't reallocated.

This function is mostly useful to pass a byte array to a function that accepts a const char *.

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() and operator[]().

const char * QByteArray::data () const

This is an overloaded member function, provided for convenience.

bool QByteArray::endsWith ( const QByteArray & ba ) const

Returns true if this byte array ends with byte array ba; otherwise returns false.

Example:

    QByteArray url("http://www.trolltech.com/index.html");
    if (url.endsWith(".html"))
        ...

See also startsWith() and right().

bool QByteArray::endsWith ( const char * str ) const

This is an overloaded member function, provided for convenience.

Returns true if this byte array ends with string str; otherwise returns false.

bool QByteArray::endsWith ( char ch ) const

This is an overloaded member function, provided for convenience.

Returns true if this byte array ends with character ch; otherwise returns false.

QByteArray & QByteArray::fill ( char ch, int size = -1 )

Sets every byte in the byte array to character ch. If size is different from -1 (the default), the byte array is resized to size size beforehand.

Example:

    QByteArray ba("Istambul");
    ba.fill("o");
    // ba == "oooooooo"

    ba.fill("X", 2);
    // ba == "XX"

See also resize().

QByteArray QByteArray::fromBase64 ( const QByteArray & base64 )   [static]

Returns a decoded copy of the Base64 array base64. For example:

    QByteArray text = QByteArray::fromBase64("UXQgaXMgZ3JlYXRcIQo=");
    text.data();            // returns "Qt is great!"

See also toBase64().

QByteArray QByteArray::fromRawData ( const char * data, int size )   [static]

Constructs a QByteArray that uses the first size characters in the array data. The bytes in data are not copied. The caller must be able to guarantee that data will not be deleted or modified as long as the QByteArray (or an unmodified copy of it) exists.

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

Here's an example of how we can read data using a QDataStream on raw data in memory without requiring to copy the data into a QByteArray:

     static const char mydata[] = {
        0x00, 0x00, 0x03, 0x84, 0x78, 0x9c, 0x3b, 0x76,
        0xec, 0x18, 0xc3, 0x31, 0x0a, 0xf1, 0xcc, 0x99,
        ...
        0x6d, 0x5b
    };

    QByteArray data = QByteArray::fromRawData(mydata, sizeof(mydata));
    QDataStream in(&data, QIODevice::ReadOnly);
    ...

Warning: A byte array created with fromRawData() is not null-terminated, unless the raw data contains a 0 character at position size. While that does not matter for QDataStream or functions like indexOf(), passing the byte array to a function that accepts a const char * and expects it to be '\0'-terminated leads into trouble.

See also data() and constData().

int QByteArray::indexOf ( const QByteArray & ba, int from = 0 ) const

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.

Example:

    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

See also lastIndexOf(), contains(), and count().

int QByteArray::indexOf ( const QString & str, int from = 0 ) const

This is an overloaded member function, provided for convenience.

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

The Unicode data is converted into 8-bit characters using QString::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 *.

int QByteArray::indexOf ( const char * str, int from = 0 ) const

This is an overloaded member function, provided for convenience.

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.

int QByteArray::indexOf ( char ch, int from = 0 ) const

This is an overloaded member function, provided for convenience.

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.

Example:

    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

See also lastIndexOf() and contains().

QByteArray & QByteArray::insert ( int i, const QByteArray & ba )

Inserts the byte array ba at index position i and returns a reference to this byte array.

Example:

    QByteArray ba("Meal");
    ba.insert(1, QByteArray("ontr"));
    // ba == "Montreal"

See also append(), prepend(), replace(), and remove().

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

This is an overloaded member function, provided for convenience.

Inserts the string str at index position i in the byte array. The Unicode data is converted into 8-bit characters using QString::toAscii().

If i is greater than size(), the array is first extended using resize().

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::insert ( int i, const char * str )

This is an overloaded member function, provided for convenience.

Inserts the string str at position i in the byte array.

If i is greater than size(), the array is first extended using resize().

QByteArray & QByteArray::insert ( int i, char ch )

This is an overloaded member function, provided for convenience.

Inserts character ch at index position i in the byte array. If i is greater than size(), the array is first extended using resize().

bool QByteArray::isEmpty () const

Returns true if the byte array has size 0; otherwise returns false.

Example:

    QByteArray().isEmpty();         // returns true
    QByteArray("").isEmpty();       // returns true
    QByteArray("abc").isEmpty();    // returns false

See also size().

bool QByteArray::isNull () const

Returns true if this byte array is null; otherwise returns false.

Example:

    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().

See also isEmpty().

int QByteArray::lastIndexOf ( const QByteArray & ba, int from = -1 ) const

Returns the index position of the last occurrence of the byte array ba in this byte array, searching backward from index position from. If from is -1 (the default), the search starts at the last byte. Returns -1 if ba could not be found.

Example:

    QByteArray x("crazy azimuths");
    QByteArray y("azy");
    x.lastIndexOf(y);           // returns 6
    x.lastIndexOf(y, 6);        // returns 6
    x.lastIndexOf(y, 5);        // returns 2
    x.lastIndexOf(y, 1);        // returns -1

See also indexOf(), contains(), and count().

int QByteArray::lastIndexOf ( const QString & str, int from = -1 ) const

This is an overloaded member function, provided for convenience.

Returns the index position of the last occurrence of the string str in the byte array, searching backward from index position from. If from is -1 (the default), the search starts at the last (size() - 1) byte. Returns -1 if str could not be found.

The Unicode data is converted into 8-bit characters using QString::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 *.

int QByteArray::lastIndexOf ( const char * str, int from = -1 ) const

This is an overloaded member function, provided for convenience.

Returns the index position of the last occurrence of the string str in the byte array, searching backward from index position from. If from is -1 (the default), the search starts at the last (size() - 1) byte. Returns -1 if str could not be found.

int QByteArray::lastIndexOf ( char ch, int from = -1 ) const

This is an overloaded member function, provided for convenience.

Returns the index position of the last occurrence of character ch in the byte array, searching backward from index position from. If from is -1 (the default), the search starts at the last (size() - 1) byte. Returns -1 if ch could not be found.

Example:

    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

See also indexOf() and contains().

QByteArray QByteArray::left ( int len ) const

Returns a byte array that contains the leftmost 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.left(4);
    // y == "Pine"

See also right(), mid(), startsWith(), and truncate().

QByteArray QByteArray::leftJustified ( int width, char fill = ' ', bool truncate = false ) const

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

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 any bytes in a copy of the byte array after position width are removed, and the copy is returned.

Example:

    QByteArray x("apple");
    QByteArray y = x.leftJustified(8, '.');   // y == "apple..."

See also rightJustified().

int QByteArray::length () const

Same as size().

QByteArray QByteArray::mid ( int pos, int len = -1 ) const

Returns a byte array containing len bytes from this byte array, starting at position pos.

If len is -1 (the default), or pos + len >= size(), returns a byte array containing all bytes starting at position pos until the end of the byte array.

Example:

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

See also left() and right().

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

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.

Example:

    int n = 63;
    QByteArray::number(n);              // returns "63"
    QByteArray::number(n, 16);          // returns "3f"
    QByteArray::number(n, 16).upper();  // returns "3F"

See also setNum() and toInt().

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

This is an overloaded member function, provided for convenience.

See also toUInt().

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

This is an overloaded member function, provided for convenience.

See also toLongLong().

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

This is an overloaded member function, provided for convenience.

See also toULongLong().

QByteArray QByteArray::number ( double n, char f = 'g', int prec = 6 )   [static]

This is an overloaded member function, provided for convenience.

Returns a byte array that contains the printed value of n, formatted in format f with precision prec.

Argument n is formatted according to the f format specified, which is g by default, and can be any of the following:

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

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).

See also append() and insert().

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

This is an overloaded member function, provided for convenience.

Prepends the string str to this byte array.

QByteArray & QByteArray::prepend ( char ch )

This is an overloaded member function, provided for convenience.

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 member function, provided for convenience.

Same as append(str).

void QByteArray::push_back ( char ch )

This is an overloaded member function, provided for convenience.

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 member function, provided for convenience.

Same as prepend(str).

void QByteArray::push_front ( char ch )

This is an overloaded member function, provided for convenience.

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::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 member function, provided for convenience.

QByteArray & QByteArray::replace ( const QByteArray & before, const QByteArray & after )

This is an overloaded member function, provided for convenience.

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 member function, provided for convenience.

Replaces every occurrence of the string before with the byte array after.

QByteArray & QByteArray::replace ( const QByteArray & before, const char * after )

This is an overloaded member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

Replaces every occurrence of the string before with the string after.

QByteArray & QByteArray::replace ( const char * before, const char * after )

This is an overloaded member function, provided for convenience.

Replaces every occurrence of the string before with the string after.

QByteArray & QByteArray::replace ( char before, const QByteArray & after )

This is an overloaded member function, provided for convenience.

Replaces every occurrence of the character before with the byte array after.

QByteArray & QByteArray::replace ( char before, const QString & after )

This is an overloaded member function, provided for convenience.

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 member function, provided for convenience.

Replaces every occurrence of the character before with the string after.

QByteArray & QByteArray::replace ( char before, char after )

This is an overloaded member function, provided for convenience.

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().

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"

See also number() and toInt().

QByteArray & QByteArray::setNum ( uint n, int base = 10 )

This is an overloaded member function, provided for convenience.

See also toUInt().

QByteArray & QByteArray::setNum ( short n, int base = 10 )

This is an overloaded member function, provided for convenience.

See also toShort().

QByteArray & QByteArray::setNum ( ushort n, int base = 10 )

This is an overloaded member function, provided for convenience.

See also toUShort().

QByteArray & QByteArray::setNum ( qlonglong n, int base = 10 )

This is an overloaded member function, provided for convenience.

See also toLongLong().

QByteArray & QByteArray::setNum ( qulonglong n, int base = 10 )

This is an overloaded member function, provided for convenience.

See also toULongLong().

QByteArray & QByteArray::setNum ( double n, char f = 'g', int prec = 6 )

This is an overloaded member function, provided for convenience.

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:

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).

See also toDouble().

QByteArray & QByteArray::setNum ( float n, char f = 'g', int prec = 6 )

This is an overloaded member function, provided for convenience.

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.

See also toFloat().

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.

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.trolltech.com/");
    if (url.startsWith("ftp:"))
        ...

See also endsWith() and left().

bool QByteArray::startsWith ( const char * str ) const

This is an overloaded member function, provided for convenience.

Returns true if this byte array starts with string str; otherwise returns false.

bool QByteArray::startsWith ( char ch ) const

This is an overloaded member function, provided for convenience.

Returns true if this byte array starts with character ch; otherwise returns false.

QByteArray QByteArray::toBase64 () const

Returns a copy of the byte array, encoded as Base64.

    QByteArray text("Qt is great!");
    text.toBase64();        // returns "UXQgaXMgZ3JlYXRcIQo="

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

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.

See also number().

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

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

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.

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("TROlltECH");
    QByteArray y = x.toLower();
    // y == "trolltech"

See also toUpper() and Note on 8-bit character comparisons.

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.

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.

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.

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.

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.

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("TROlltECH");
    QByteArray y = x.toUpper();
    // y == "TROLLTECH"

See also toLower() and Note on 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.

This operator is mostly useful to pass a byte array to a function that accepts a const char *.

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 void pointer to the data.

This operator is mostly useful to pass a byte array to a function that accepts a void *.

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"

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

See also append() and prepend().

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

This is an overloaded member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

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().

const char QByteArray::operator[] ( int i ) const

This is an overloaded member function, provided for convenience.

Same as at(i).

QByteRef QByteArray::operator[] ( uint i )

This is an overloaded member function, provided for convenience.

const char QByteArray::operator[] ( uint i ) const

This is an overloaded member function, provided for convenience.

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).

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 member function, provided for convenience.

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.

See also qCompress().

QByteArray qUncompress ( const uchar * data, int nbytes )

This is an overloaded member function, provided for convenience.

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 a random non-zero value if str1 is 0 or str2 is 0 (but not both).

See also qstrncmp(), qstricmp(), qstrnicmp(), and Note on 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 Note on 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.

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 Note on 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.

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 Note on 8-bit character comparisons.

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 member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

Returns true if string a1 is not equal to byte array a2; otherwise returns false.

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+=().

const QByteArray operator+ ( const QByteArray & a1, const char * a2 )

This is an overloaded member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

Returns a byte array that is the result of concatenating character a1 and byte array a2.

bool operator< ( const QByteArray & a1, const QByteArray & a2 )

This is an overloaded member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

Returns true if string a1 is lexically less than byte array a2; otherwise returns false.

QDataStream & operator<< ( QDataStream & out, const QByteArray & ba )

This is an overloaded member function, provided for convenience.

Writes byte array ba to the stream out and returns a reference to the stream.

See also Format of the QDataStream operators.

bool operator<= ( const QByteArray & a1, const QByteArray & a2 )

This is an overloaded member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

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 member function, provided for convenience.

Returns true if string a1 is lexically greater than or equal to byte array a2; otherwise returns false.

QDataStream & operator>> ( QDataStream & in, QByteArray & ba )

This is an overloaded member function, provided for convenience.

Reads a byte array into ba from the stream in and returns a reference to the stream.

See also Format of the QDataStream operators.