QDataStream Class Reference

The QDataStream class provides basic functions for serialization of binary data to a QIODevice. More...

#include <qdatastream.h>

List of all member functions.

Public Members

• QDataStream () 
• QDataStream ( QIODevice * ) 
• QDataStream ( QByteArray, int mode ) 
• virtual ~QDataStream () 
• QIODevice* device () const
• void setDevice ( QIODevice * ) 
• void unsetDevice () 
• bool atEnd () const
• bool eof () const
• enum ByteOrder { BigEndian, LittleEndian }
• int byteOrder () const
• void setByteOrder ( int ) 
• bool isPrintableData () const
• void setPrintableData ( bool ) 
• int version () const
• void setVersion ( int ) 
• QDataStream& operator>> ( Q_INT8 & i ) 
• QDataStream& operator>> ( Q_UINT8 & i ) 
• QDataStream& operator>> ( Q_INT16 & i ) 
• QDataStream& operator>> ( Q_UINT16 & i ) 
• QDataStream& operator>> ( Q_INT32 & i ) 
• QDataStream& operator>> ( Q_UINT32 & i ) 
• QDataStream& operator>> ( float & f ) 
• QDataStream& operator>> ( double & f ) 
• QDataStream& operator>> ( char *& str ) 
• QDataStream& operator<< ( Q_INT8 i ) 
• QDataStream& operator<< ( Q_UINT8 i ) 
• QDataStream& operator<< ( Q_INT16 i ) 
• QDataStream& operator<< ( Q_UINT16 i ) 
• QDataStream& operator<< ( Q_INT32 i ) 
• QDataStream& operator<< ( Q_UINT32 i ) 
• QDataStream& operator<< ( float f ) 
• QDataStream& operator<< ( double f ) 
• QDataStream& operator<< ( const char * str ) 
• QDataStream& readBytes ( char *&, uint & len ) 
• QDataStream& readRawBytes ( char *, uint len ) 
• QDataStream& writeBytes ( const char *, uint len ) 
• QDataStream& writeRawBytes ( const char *, uint len ) 

Detailed Description

A data stream is a binary stream of encoded information which is 100% independent of the host computer operation system, CPU or byte order. A stream that is written by a PC under DOS/Windows can easily be read by a Sun SPARC running Solaris.

The QDataStream class implements serialization of primitive types, like char, short, int, char* etc. Serialization of more complex data is accomplished by breaking up the data into primitive units.

The programmer can select which byte order to use when serializing data. The default setting is big endian (MSB first). Changing it to little endian breaks the portability. We therefore recommend keeping this setting unless you have special needs or requirements.

A data stream cooperates closely with a QIODevice. A QIODevice represents an input/output medium one can read data from and write data to. The QFile class is an example of an IO device.

Example (write data to a stream):

    QFile f( "file.dta" );
    f.open( IO_WriteOnly );                     // open file for writing
    QDataStream s( &f );                        // serialize using f
    s << "the answer is";                       // serialize string
    s << (Q_INT32)42;                           // serialize integer
    f.close();                                  // done

Example (read data from a stream):

    QFile f( "file.dta" );
    f.open( IO_ReadOnly );                      // open file for reading
    QDataStream s( &f );                        // serialize using f
    char   *str;
    Q_INT32 a;
    s >> str >> a;                              // "the answer is" and 42
    f.close();                                  // done
    delete str;                                 // delete string

In the last example, if you read into a QString instead of a char* you do not have to delete it.

See also: QTextStream.

Member Function Documentation

QDataStream::QDataStream ()

Constructs a data stream that has no IO device.

QDataStream::QDataStream ( QIODevice * d )

Constructs a data stream that uses the IO device d.

QDataStream::QDataStream ( QByteArray a, int mode )

Constructs a data stream that operates on a byte array through an internal QBuffer device.

Example:

    static char bindata[] = { 231, 1, 44, ... };
    QByteArray  a;
    a.setRawData( bindata, sizeof(bindata) );   // a points to bindata
    QDataStream s( a, IO_ReadOnly );            // open on a's data
    s >> <something>;                           // read raw bindata
    a.resetRawData( bindata, sizeof(bindata) ); // finished

The QArray::setRawData() function is not for the inexperienced.

QDataStream::~QDataStream () [virtual]

Destroys the data stream.

The destructor will not affect the current IO device, unless it is an internal IO device processing a QByteArray passed in the constructor.

bool QDataStream::atEnd () const

Returns TRUE if the IO device has reached the end position (end of stream or file) or if there is no IO device set.

Returns FALSE if the current position of the read/write head of the IO device is somewhere before the end position.

See also: QIODevice::atEnd().

int QDataStream::byteOrder () const

Returns the current byte order setting.

See also: setByteOrder().

QIODevice * QDataStream::device () const

Returns the IO device currently set.

See also: setDevice() and unsetDevice().

bool QDataStream::eof () const

This function is obsolete. It is provided to keep old programs working. We strongly advise against using it in new code.

Returns TRUE if the IO device has reached the end position (end of stream or file) or if there is no IO device set.

Returns FALSE if the current position of the read/write head of the IO device is somewhere before the end position.

See also: QIODevice::atEnd().

bool QDataStream::isPrintableData () const

Returns TRUE if the printable data flag has been set.

See also: setPrintableData().

QDataStream & QDataStream::operator<< ( Q_INT16 i )

Writes a signed 16-bit integer to the stream and returns a reference to the stream.

QDataStream & QDataStream::operator<< ( Q_INT32 i )

Writes a signed 32-bit integer to the stream and returns a reference to the stream.

QDataStream & QDataStream::operator<< ( Q_INT8 i )

Writes a signed byte to the stream.

QDataStream & QDataStream::operator<< ( Q_UINT16 i )

Writes an unsigned 16-bit integer to the stream and returns a reference to the stream.

QDataStream & QDataStream::operator<< ( Q_UINT32 i )

Writes an unsigned 32-bit integer to the stream and returns a reference to the stream.

QDataStream & QDataStream::operator<< ( Q_UINT8 i )

Writes an unsigned byte to the stream and returns a reference to the stream.

QDataStream & QDataStream::operator<< ( const char * s )

Writes the '\0'-terminated string s to the stream and returns a reference to the stream.

The string is serialized using writeBytes().

QDataStream & QDataStream::operator<< ( double f )

Writes a 64-bit floating point number to the stream using the standard IEEE754 format. Returns a reference to the stream.

QDataStream & QDataStream::operator<< ( float f )

Writes a 32-bit floating point number to the stream using the standard IEEE754 format. Returns a reference to the stream.

QDataStream & QDataStream::operator>> ( Q_INT16 & i )

Reads a signed 16-bit integer from the stream and returns a reference to the stream.

QDataStream & QDataStream::operator>> ( Q_INT32 & i )

Reads a signed 32-bit integer from the stream and returns a reference to the stream.

QDataStream & QDataStream::operator>> ( Q_INT8 & i )

Reads a signed byte from the stream.

QDataStream & QDataStream::operator>> ( Q_UINT16 & i )

Reads an unsigned 16-bit integer from the stream and returns a reference to the stream.

QDataStream & QDataStream::operator>> ( Q_UINT32 & i )

Reads an unsigned 32-bit integer from the stream and returns a reference to the stream.

QDataStream & QDataStream::operator>> ( Q_UINT8 & i )

Reads an unsigned byte from the stream and returns a reference to the stream.

QDataStream & QDataStream::operator>> ( char *& s )

Reads the '\0'-terminated string s from the stream and returns a reference to the stream.

The string is read using readBytes(), which allocates space using new.

QDataStream & QDataStream::operator>> ( double & f )

Reads a 64-bit floating point number from the stream using the standard IEEE754 format. Returns a reference to the stream.

QDataStream & QDataStream::operator>> ( float & f )

Reads a 32-bit floating point number from the stream using the standard IEEE754 format. Returns a reference to the stream.

QDataStream & QDataStream::readBytes ( char *& s, uint & l )

Reads the buffer s from the stream and returns a reference to the stream.

The buffer s is allocated using new. Destroy it with the delete operator. If the length is zero or s cannot be allocated, s is set to 0.

The l parameter will be set to the length of the buffer.

The serialization format is an Q_UINT32 length specifier first, then the data (length bytes).

See also: readRawBytes() and writeBytes().

QDataStream & QDataStream::readRawBytes ( char * s, uint len )

Reads len bytes from the stream into e s and returns a reference to the stream.

The buffer s must be preallocated.

See also: readBytes(), QIODevice::readBlock() and writeRawBytes().

void QDataStream::setByteOrder ( int bo )

Sets the serialization byte order to bo.

The bo parameter can be QDataStream::BigEndian or QDataStream::LittleEndian.

The default setting is big endian. We recommend leaving this setting unless you have special requirements.

See also: byteOrder().

void QDataStream::setDevice ( QIODevice * d )

void QDataStream::setDevice(QIODevice *d ) Sets the IO device to d.

See also: device() and unsetDevice().

void QDataStream::setPrintableData ( bool enable )

Sets or clears the printable data flag.

If this flag is set, the write functions will generate output that consists of printable characters (7 bit ASCII).

We recommend enabling printable data only for debugging purposes (it is slower and creates bigger output).

void QDataStream::setVersion ( int v )

Sets the version number of the data serialization format.

In Qt 2.0, the datastream serialization format of many Qt classes was changed. In order to read data that was created with the QDatastream of Qt 1.x, call this function with the version number \v set to 1.

See also: version().

void QDataStream::unsetDevice ()

Unsets the IO device. This is the same as calling setDevice( 0 ).

See also: device() and setDevice().

int QDataStream::version () const

Returns the version number of the data serialization format. In Qt 2.0, this number is 2.

See also: setVersion().

QDataStream & QDataStream::writeBytes ( const char * s, uint len )

Writes the length specifier len and the buffer s to the stream and returns a reference to the stream.

The len is serialized as an Q_UINT32, followed by len bytes from s.

See also: writeRawBytes() and readBytes().

QDataStream & QDataStream::writeRawBytes ( const char * s, uint len )

Writes len bytes from s to the stream and returns a reference to the stream.

See also: writeBytes(), QIODevice::writeBlock() and readRawBytes().

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