Qt 4.3: QByteArray Class Reference

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# QByteArray Class Reference
[QtCore module]

The QByteArray class provides an array of bytes. More...

     #include <QByteArray>

Inherited by Q3CString.

Note: All the functions in this class are reentrant.

- List of all members, including inherited members
- Qt 3 support members

### Public Functions

- QByteArray ()
- QByteArray ( const char * str )
- QByteArray ( const char * data, int size )
- QByteArray ( int size, char ch )
- QByteArray ( const QByteArray & other )
- ~QByteArray ()
- QByteArray & append ( const QByteArray & ba )
- QByteArray & append ( const QString & str )
- QByteArray & append ( const char * str )
- QByteArray & append ( char ch )
- const char at ( int i ) const
- int capacity () const
- void chop ( int n )
- void clear ()
- const char * constData () const
- bool contains ( const QByteArray & ba ) const
- bool contains ( const char * str ) const
- bool contains ( char ch ) const
- int count ( const QByteArray & ba ) const
- int count ( const char * str ) const
- int count ( char ch ) const
- int count () const
- char * data ()
- const char * data () const
- bool endsWith ( const QByteArray & ba ) const
- bool endsWith ( const char * str ) const
- bool endsWith ( char ch ) const
- QByteArray & fill ( char ch, int size = -1 )
- int indexOf ( const QByteArray & ba, int from = 0 ) const
- int indexOf ( const QString & str, int from = 0 ) const
- int indexOf ( const char * str, int from = 0 ) const
- int indexOf ( char ch, int from = 0 ) const
- QByteArray & insert ( int i, const QByteArray & ba )
- QByteArray & insert ( int i, const QString & str )
- QByteArray & insert ( int i, const char * str )
- QByteArray & insert ( int i, char ch )
- bool isEmpty () const
- bool isNull () const
- int lastIndexOf ( const QByteArray & ba, int from = -1 ) const
- int lastIndexOf ( const QString & str, int from = -1 ) const
- int lastIndexOf ( const char * str, int from = -1 ) const
- int lastIndexOf ( char ch, int from = -1 ) const
- QByteArray left ( int len ) const
- QByteArray leftJustified ( int width, char fill = ' ', bool truncate = false ) const
- int length () const
- QByteArray mid ( int pos, int len = -1 ) const
- QByteArray & prepend ( const QByteArray & ba )
- QByteArray & prepend ( const char * str )
- QByteArray & prepend ( char ch )
- void push_back ( const QByteArray & other )
- void push_back ( const char * str )
- void push_back ( char ch )
- void push_front ( const QByteArray & other )
- void push_front ( const char * str )
- void push_front ( char ch )
- QByteArray & remove ( int pos, int len )
- QByteArray & replace ( int pos, int len, const QByteArray & after )
- QByteArray & replace ( int pos, int len, const char * after )
- QByteArray & replace ( const QByteArray & before, const QByteArray & after )
- QByteArray & replace ( const char * before, const QByteArray & after )
- QByteArray & replace ( const QByteArray & before, const char * after )
- QByteArray & replace ( const QString & before, const QByteArray & after )
- QByteArray & replace ( const QString & before, const char * after )
- QByteArray & replace ( const char * before, const char * after )
- QByteArray & replace ( char before, const QByteArray & after )
- QByteArray & replace ( char before, const QString & after )
- QByteArray & replace ( char before, const char * after )
- QByteArray & replace ( char before, char after )
- void reserve ( int size )
- void resize ( int size )
- QByteArray right ( int len ) const
- QByteArray rightJustified ( int width, char fill = ' ', bool truncate = false ) const
- QByteArray & setNum ( int n, int base = 10 )
- QByteArray & setNum ( uint n, int base = 10 )
- QByteArray & setNum ( short n, int base = 10 )
- QByteArray & setNum ( ushort n, int base = 10 )
- QByteArray & setNum ( qlonglong n, int base = 10 )
- QByteArray & setNum ( qulonglong n, int base = 10 )
- QByteArray & setNum ( double n, char f = 'g', int prec = 6 )
- QByteArray & setNum ( float n, char f = 'g', int prec = 6 )
- QByteArray simplified () const
- int size () const
- QList<QByteArray> split ( char sep ) const
- void squeeze ()
- bool startsWith ( const QByteArray & ba ) const
- bool startsWith ( const char * str ) const
- bool startsWith ( char ch ) const
- QByteArray toBase64 () const
- double toDouble ( bool * ok = 0 ) const
- float toFloat ( bool * ok = 0 ) const
- QByteArray toHex () const
- int toInt ( bool * ok = 0, int base = 10 ) const
- long toLong ( bool * ok = 0, int base = 10 ) const
- qlonglong toLongLong ( bool * ok = 0, int base = 10 ) const
- QByteArray toLower () const
- short toShort ( bool * ok = 0, int base = 10 ) const
- uint toUInt ( bool * ok = 0, int base = 10 ) const
- ulong toULong ( bool * ok = 0, int base = 10 ) const
- qulonglong toULongLong ( bool * ok = 0, int base = 10 ) const
- ushort toUShort ( bool * ok = 0, int base = 10 ) const
- QByteArray toUpper () const
- QByteArray trimmed () const
- void truncate ( int pos )
- operator const char * () const
- operator const void * () const
- bool operator!= ( const QString & str ) const
- QByteArray & operator+= ( const QByteArray & ba )
- QByteArray & operator+= ( const QString & str )
- QByteArray & operator+= ( const char * str )
- QByteArray & operator+= ( char ch )
- bool operator< ( const QString & str ) const
- bool operator<= ( const QString & str ) const
- QByteArray & operator= ( const QByteArray & other )
- QByteArray & operator= ( const char * str )
- bool operator== ( const QString & str ) const
- bool operator> ( const QString & str ) const
- bool operator>= ( const QString & str ) const
- QByteRef operator[] ( int i )
- const char operator[] ( int i ) const
- QByteRef operator[] ( uint i )
- const char operator[] ( uint i ) const

### Static Public Members

- QByteArray fromBase64 ( const QByteArray & base64 )
- QByteArray fromHex ( const QByteArray & hexEncoded )
- QByteArray fromRawData ( const char * data, int size )
- QByteArray number ( int n, int base = 10 )
- QByteArray number ( uint n, int base = 10 )
- QByteArray number ( qlonglong n, int base = 10 )
- QByteArray number ( qulonglong n, int base = 10 )
- QByteArray number ( double n, char f = 'g', int prec = 6 )

### Related Non-Members

- quint16 qChecksum ( const char * data, uint len )
- QByteArray qCompress ( const QByteArray & data, int compressionLevel = -1 )
- QByteArray qCompress ( const uchar * data, int nbytes, int compressionLevel = -1 )
- QByteArray qUncompress ( const QByteArray & data )
- QByteArray qUncompress ( const uchar * data, int nbytes )
- int qsnprintf ( char * str, size_t n, const char * fmt, ... )
- int qstrcmp ( const char * str1, const char * str2 )
- char * qstrcpy ( char * dst, const char * src )
- char * qstrdup ( const char * src )
- int qstricmp ( const char * str1, const char * str2 )
- uint qstrlen ( const char * str )
- int qstrncmp ( const char * str1, const char * str2, uint len )
- char * qstrncpy ( char * dst, const char * src, uint len )
- int qstrnicmp ( const char * str1, const char * str2, uint len )
- uint qstrnlen ( const char * str, uint maxlen )
- int qvsnprintf ( char * str, size_t n, const char * fmt, va_list ap )
- bool operator!= ( const QByteArray & a1, const QByteArray & a2 )
- bool operator!= ( const QByteArray & a1, const char * a2 )
- bool operator!= ( const char * a1, const QByteArray & a2 )
- const QByteArray operator+ ( const QByteArray & a1, const QByteArray & a2 )
- const QByteArray operator+ ( const QByteArray & a1, const char * a2 )
- const QByteArray operator+ ( const QByteArray & a1, char a2 )
- const QByteArray operator+ ( const char * a1, const QByteArray & a2 )
- const QByteArray operator+ ( char a1, const QByteArray & a2 )
- bool operator< ( const QByteArray & a1, const QByteArray & a2 )
- bool operator< ( const QByteArray & a1, const char * a2 )
- bool operator< ( const char * a1, const QByteArray & a2 )
- QDataStream & operator<< ( QDataStream & out, const QByteArray & ba )
- bool operator<= ( const QByteArray & a1, const QByteArray & a2 )
- bool operator<= ( const QByteArray & a1, const char * a2 )
- bool operator<= ( const char * a1, const QByteArray & a2 )
- bool operator== ( const QByteArray & a1, const QByteArray & a2 )
- bool operator== ( const QByteArray & a1, const char * a2 )
- bool operator== ( const char * a1, const QByteArray & a2 )
- bool operator> ( const QByteArray & a1, const QByteArray & a2 )
- bool operator> ( const QByteArray & a1, const char * a2 )
- bool operator> ( const char * a1, const QByteArray & a2 )
- bool operator>= ( const QByteArray & a1, const QByteArray & a2 )
- bool operator>= ( const QByteArray & a1, const char * a2 )
- bool operator>= ( const char * a1, const QByteArray & a2 )
- QDataStream & operator>> ( QDataStream & in, QByteArray & ba )

## Detailed Description

The 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 Qtopia Core).

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. 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().

### 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. For read-only access, constData() is faster because it never causes a deep copy to occur.

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. Input is not checked for validity; invalid characters in the input are skipped, enabling the decoding process to continue with subsequent characters.

For example:

     QByteArray text = QByteArray::fromBase64("UXQgaXMgZ3JlYXQh");
     text.data();            // returns "Qt is great!"

The algorithm used to decode Base64-encoded data is defined in RFC 2045.

See also toBase64().

### QByteArray QByteArray::fromHex ( const QByteArray & hexEncoded ) `[static]`

Returns a decoded copy of the hex encoded array hexEncoded. Input is not checked for validity; invalid characters in the input are skipped, enabling the decoding process to continue with subsequent characters.

For example:

     QByteArray text = QByteArray::fromHex("517420697320677265617421");
     text.data();            // returns "Qt is great!"

See also toHex().

### 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).toUpper();  // 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:

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

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:

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).

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 "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

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().

### 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

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.

Note: If you want to use this function to uncompress external data compressed using zlib, you first need to prepend four bytes to the byte array that contain the expected length of the uncompressed data encoded in big-endian order (most significant byte first).

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 an arbitrary 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.

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 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.

### 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 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.