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QBuffer Class Reference

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

#include <qbuffer.h>

Inherits QIODevice.

List of all member functions.

Public Members

• QBuffer () 
• QBuffer ( QByteArray ) 
• ~QBuffer () 
• QByteArray buffer () const
• bool setBuffer ( QByteArray ) 

Detailed Description

QBuffer allows reading and writing a memory buffer. It is normally used together 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 with an existing byte array. The byte array can also be set with setBuffer(). Writing to the QBuffer will modify the original byte array, since 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().

The 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 and Shared Classes

Examples: grapher/grapher.cpp

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 \0
    b.writeBlock( "def", 4 );                   // write including \0
    b.close();
      // Now, str == "abcdef"

See also setBuffer().

QBuffer::~QBuffer ()

Destructs the buffer.

bool QBuffer::at ( int pos ) [virtual]

Reimplemented for internal reasons; the API is not affected.

Reimplemented from QIODevice.

int QBuffer::at () const [virtual]

Reimplemented for internal reasons; the API is not affected.

Reimplemented from QIODevice.

QByteArray QBuffer::buffer () const

Returns this buffer's byte array.

See also setBuffer().

void QBuffer::close () [virtual]

Reimplemented for internal reasons; the API is not affected. Closes an open buffer.

See also open().

Examples: grapher/grapher.cpp

Reimplemented from QIODevice.

void QBuffer::flush () [virtual]

Reimplemented for internal reasons; the API is not affected. The flush function does nothing for a QBuffer.

Reimplemented from QIODevice.

int QBuffer::getch () [virtual]

Reimplemented for internal reasons; the API is not affected.

Reimplemented from QIODevice.

bool QBuffer::open ( int m ) [virtual]

Reimplemented for internal reasons; the API is not affected. Opens the buffer in the mode m. Returns TRUE if successful, otherwise FALSE. The buffer must be opened before use.

The mode parameter m must be a combination of the following flags.

• IO_ReadOnly opens a buffer in read-only mode.
• IO_WriteOnly opens a buffer in write-only mode.
• IO_ReadWrite opens a buffer in read/write mode.
• IO_Append sets the buffer index to the end of the buffer.
• IO_Truncate truncates the buffer.

See also close() and isOpen().

Examples: grapher/grapher.cpp

Reimplemented from QIODevice.

int QBuffer::putch ( int ch ) [virtual]

Reimplemented for internal reasons; the API is not affected. Writes the character ch into the buffer, overwriting the character at the current index, extending the buffer if necessary.

Returns ch, or -1 if some error occurred.

See also getch() and ungetch().

Examples: grapher/grapher.cpp

Reimplemented from QIODevice.

int QBuffer::readBlock ( char * p, uint len ) [virtual]

Reimplemented for internal reasons; the API is not affected.

Reimplemented from QIODevice.

int QBuffer::readLine ( char * p, uint maxlen ) [virtual]

Reimplemented for internal reasons; the API is not affected.

Reimplemented from QIODevice.

bool QBuffer::setBuffer ( QByteArray buf )

Replaces the buffer's contents with buf.

This may not be done when 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().

uint QBuffer::size () const [virtual]

Reimplemented for internal reasons; the API is not affected.

Reimplemented from QIODevice.

int QBuffer::ungetch ( int ch ) [virtual]

Reimplemented for internal reasons; the API is not affected.

Reimplemented from QIODevice.

int QBuffer::writeBlock ( const char * p, uint len ) [virtual]

Reimplemented for internal reasons; the API is not affected.

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

Returns -1 if a serious error occurred.

See also readBlock().

Reimplemented from QIODevice.

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