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# QBuffer Class Reference

The QBuffer class is an I/O device that operates on a QByteArray. More...

All the functions in this class are reentrant when Qt is built with thread support.

`#include <qbuffer.h>`

Inherits QIODevice.

List of all member functions.

## Public Members

- QBuffer ()
- QBuffer ( QByteArray buf )
- ~QBuffer ()
- QByteArray buffer () const
- bool setBuffer ( QByteArray buf )
- virtual Q_LONG writeBlock ( const char * p, Q_ULONG len )
- Q_LONG writeBlock ( const QByteArray & data )

## Detailed Description

The QBuffer class is an I/O device that operates on a QByteArray.

QBuffer is used to read and write to a memory buffer. It is normally used with a QTextStream or a QDataStream. QBuffer has an associated QByteArray which holds the buffer data. The size() of the buffer is automatically adjusted as data is written.

The constructor `QBuffer(QByteArray)` creates a QBuffer using an existing byte array. The byte array can also be set with setBuffer(). Writing to the QBuffer will modify the original byte array because QByteArray is explicitly shared.

Use open() to open the buffer before use and to set the mode (read-only, write-only, etc.). close() closes the buffer. The buffer must be closed before reopening or calling setBuffer().

A common way to use QBuffer is through QDataStream or QTextStream, which have constructors that take a QBuffer parameter. For convenience, there are also QDataStream and QTextStream constructors that take a QByteArray parameter. These constructors create and open an internal QBuffer.

Note that QTextStream can also operate on a QString (a Unicode string); a QBuffer cannot.

You can also use QBuffer directly through the standard QIODevice functions readBlock(), writeBlock() readLine(), at(), getch(), putch() and ungetch().

See also QFile, QDataStream, QTextStream, QByteArray, Shared Classes, Collection Classes, and Input/Output and Networking.

## Member Function Documentation

### QBuffer::QBuffer ()

Constructs an empty buffer.

### QBuffer::QBuffer ( QByteArray buf )

Constructs a buffer that operates on buf.

If you open the buffer in write mode (IO_WriteOnly or IO_ReadWrite) and write something into the buffer, buf will be modified.

Example:

        QCString str = "abc";
        QBuffer b( str );
        b.open( IO_WriteOnly );
        b.at( 3 ); // position at the 4th character (the terminating \0)
        b.writeBlock( "def", 4 ); // write "def" including the terminating \0
        b.close();
        // Now, str == "abcdef" with a terminating \0

See also setBuffer().

### QBuffer::~QBuffer ()

Destroys the buffer.

### QByteArray QBuffer::buffer () const

Returns this buffer's byte array.

See also setBuffer().

### bool QBuffer::setBuffer ( QByteArray buf )

Replaces the buffer's contents with buf and returns TRUE.

Does nothing (and returns FALSE) if isOpen() is TRUE.

Note that if you open the buffer in write mode (IO_WriteOnly or IO_ReadWrite) and write something into the buffer, buf is also modified because QByteArray is an explicitly shared class.

See also buffer(), open(), and close().

### Q_LONG QBuffer::writeBlock ( const char * p, Q_ULONG len )`[virtual]`

Writes len bytes from p into the buffer at the current index position, overwriting any characters there and extending the buffer if necessary. Returns the number of bytes actually written.

Returns -1 if an error occurred.

See also readBlock().

Reimplemented from QIODevice.

### Q_LONG QBuffer::writeBlock ( const QByteArray & data )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

This convenience function is the same as calling `writeBlock( data.data(), data.size() )` with data.

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