QDataStream(3qt)QDataStream(3qt)NAMEQDataStream - Serialization of binary data to a
#include <qdatastream.h>
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 (obsolete)
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>> ( Q_INT64 & i )
QDataStream& operator>> ( Q_UINT64 & 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<< ( Q_INT64 i )
QDataStream& operator<< ( Q_UINT64 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 )
DESCRIPTION
The QDataStream class provides serialization of binary
data to a QIODevice.
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QDataStream(3qt)QDataStream(3qt)
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 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 (unless the reader also changes to little
endian). We recommend keeping this setting unless you have
special 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
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
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.
Normally, each item written to the stream is written in a
fixed binary format. For example, a char* is written as a
32-bit integer equal to the length of the string including
the NUL byte, followed by all the characters of the string
including the NUL byte. Similarly when reading a string, 4
bytes are read to create the 32-bit length value, then
that many characters for the string including the NUL. For
a complete description of all Qt types supporting data
streaming see Format of the QDataStream operators .
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If you want a "parsing" input stream, see QTextStream. If
you just want the data to be human-readable to aid in
debugging, you can set the data stream into printable data
mode with setPrintableData(). The data is then written
slower, in a human readable bloated form that is
sufficient for debugging.
If you are producing a new binary data format, such as a
file format for documents created by your application, you
could use a QDataStream to write the data in a portable
format. Typically, you would write a brief header
containing a magic string and a version number to give
yourself room for future expansion. For example:
// Open the file.
QFile f( "file.xxx" );
f.open( IO_WriteOnly );
QDataStream s( &f );
// Write a header with a "magic number" and a version
s << 0xa0b0c0d0;
s << 123;
// Write the data
s << [lots of interesting data]
Then read it in with:
// Open the file.
QFile f( "file.xxx" );
f.open( IO_ReadOnly );
QDataStream s( &f );
// Read and check the header
Q_UINT32 magic;
s >> magic;
if ( magic != 0xa0b0c0d0 )
return XXX_BAD_FILE_FORMAT;
// Read the version
Q_INT32 version;
s >> version;
if ( version < 100 )
return XXX_BAD_FILE_TOO_OLD;
if ( version > 123 )
return XXX_BAD_FILE_TOO_NEW;
if ( version <= 110 )
s.setVersion(1);
// Read the data
s >> [lots of interesting data];
if ( version > 120 )
s >> [data new in XXX version 1.2];
s >> [other interesting data];
See also QTextStream and QVariant.
MEMBER FUNCTION DOCUMENTATIONTrolltech AS 13 June 2001 3
QDataStream(3qt)QDataStream(3qt)QDataStream::QDataStream ()
Constructs a data stream that has no IO device.
See also setDevice().
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 ( QIODevice * d )
Constructs a data stream that uses the IO device d.
See also setDevice() and device().
QDataStream::~QDataStream () [virtual]
Destructs 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 - either BigEndian
or LittleEndian.
See also setByteOrder().
QIODevice * QDataStream::device () const
Returns the IO device currently set.
See also setDevice() and unsetDevice().
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QDataStream(3qt)QDataStream(3qt)bool QDataStream::eof () const
This function is obsolete. It is provided to keep old
source working, and will probably be removed in a future
version of Qt. 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_INT64 i )
Writes a signed 64-bit integer to the stream and returns a
reference to the stream, or calls the Q_INT32-operator if
64 bit is not available.
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_UINT64 i )
Writes an unsigned 64-bit integer to the stream and
returns a reference to the stream, or uses the
Q_UINT32-operator if 64 bit is not available.
QDataStream & QDataStream::operator<;< ( Q_UINT8 i )
Writes an unsigned byte to the stream and returns a
reference to the stream.
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QDataStream(3qt)QDataStream(3qt)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_INT64 & i )
Reads a signed 64-bit integer from the stream and returns
a reference to the stream, or uses the Q_UINT32 operator
if 64 bit is not available.
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_UINT64 & i )
Reads an unsigned 64-bit integer from the stream and
returns a reference to the stream, or uses the Q_UINT32
operator if 64 bit is not available.
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.
Space for the string is allocated using new - the caller
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must eventually call delete[] on the value.
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 (l bytes).
See also readRawBytes() and writeBytes().
QDataStream & QDataStream::readRawBytes ( char * s, uint len )
Reads len bytes from the stream into 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().
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QDataStream(3qt)QDataStream(3qt)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 larger output).
void QDataStream::setVersion ( int v )
Sets the version number of the data serialization format.
In order to accomodate for new functionality, the
datastream serialization format of some Qt classes has
changed in some versions of Qt. If you want to read data
that was created by an earlier version of Qt, or write
data that can be read by a program that was compiled with
an earlier version of Qt, use this function to modify the
serialization format of QDataStream.
For Qt 1.x compatibility, use v == 1.
For Qt 2.0.x compatibility, use v == 2 (Not required for
reading in Qt 2.1).
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 2.1, this number is by default 3.
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.
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QDataStream(3qt)QDataStream(3qt)
See also writeBytes(), QIODevice::writeBlock() and
readRawBytes().
SEE ALSO
http://doc.trolltech.com/qdatastream.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2001 Trolltech AS,
http://www.trolltech.com. See the license file included
in the distribution for a complete license statement.
AUTHOR
Generated automatically from the source code.
BUGS
If you find a bug in Qt, please report it as described in
http://doc.trolltech.com/bughowto.html. Good bug reports
make our job much simpler. Thank you.
In case of content or formattting problems with this
manual page, please report them to qt-bugs@trolltech.com.
Please include the name of the manual page
(qdatastream.3qt) and the Qt version (2.3.1).
Trolltech AS 13 June 2001 9
