QBuffer Class Reference
[QtCore module]

Detailed Description

The QBuffer class provides a QIODevice interface for a QByteArray.

QBuffer allows you to access a QByteArray using the QIODevice interface. The QByteArray is treated just as a standard random-accessed file. Example:

     QBuffer buffer;
     char ch;

     buffer.open(QBuffer::ReadWrite);
     buffer.write("Qt rocks!");
     buffer.seek(0);
     buffer.getChar(&ch);  // ch == 'Q'
     buffer.getChar(&ch);  // ch == 't'
     buffer.getChar(&ch);  // ch == ' '
     buffer.getChar(&ch);  // ch == 'r'

By default, an internal QByteArray buffer is created for you when you create a QBuffer. You can access this buffer directly by calling buffer(). You can also use QBuffer with an existing QByteArray by calling setBuffer(), or by passing your array to QBuffer's constructor.

Call open() to open the buffer. Then call write() or putChar() to write to the buffer, and read(), readLine(), readAll(), or getChar() to read from it. size() returns the current size of the buffer, and you can seek to arbitrary positions in the buffer by calling seek(). When you are done with accessing the buffer, call close().

The following code snippet shows how to write data to a QByteArray using QDataStream and QBuffer:

     QByteArray byteArray;
     QBuffer buffer(&byteArray);
     buffer.open(QIODevice::WriteOnly);

     QDataStream out(&buffer);
     out << QApplication::palette();

Effectively, we convert the application's QPalette into a byte array. Here's how to read the data from the QByteArray:

     QPalette palette;
     QBuffer buffer(&byteArray);
     buffer.open(QIODevice::ReadOnly);

     QDataStream in(&buffer);
     in >> palette;

QTextStream and QDataStream also provide convenience constructors that take a QByteArray and that create a QBuffer behind the scenes.

QBuffer emits readyRead() when new data has arrived in the buffer. By connecting to this signal, you can use QBuffer to store temporary data before processing it. For example, you can pass the buffer to QFtp when downloading a file from an FTP server. Whenever a new payload of data has been downloaded, readyRead() is emitted, and you can process the data that just arrived. QBuffer also emits bytesWritten() every time new data has been written to the buffer.

See also QFile, QDataStream, QTextStream, and QByteArray.

Member Function Documentation

     QByteArray byteArray("abc");
     QBuffer buffer(&byteArray);
     buffer.open(QIODevice::WriteOnly);
     buffer.seek(3);
     buffer.write("def", 3);
     buffer.close();
     // byteArray == "abcdef"

     QByteArray byteArray("abc");
     QBuffer buffer;
     buffer.setBuffer(&byteArray);
     buffer.open(QIODevice::WriteOnly);
     buffer.seek(3);
     buffer.write("def", 3);
     buffer.close();
     // byteArray == "abcdef"