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

Public Types
enum	ByteOrder

enum	FloatingPointPrecision

enum	Status

enum	Version

Public Methods
	QDataStream ()

	QDataStream (const QByteArray &buffer)

	QDataStream (QByteArray *buffer, QIODevice::OpenMode mode)

	QDataStream (QIODevice *device)

virtual	~QDataStream ()

bool	atEnd () const

ByteOrder	byteOrder () const

QIODevice *	device () const

FloatingPointPrecision	floatingPointPrecision () const

QDataStream &	operator<< (bool i)

QDataStream &	operator<< (const char *str)

QDataStream &	operator<< (double f)

QDataStream &	operator<< (float f)

QDataStream &	operator<< (long i)

QDataStream &	operator<< (qint16 i)

QDataStream &	operator<< (qint32 i)

QDataStream &	operator<< (qint64 i)

QDataStream &	operator<< (qint8 i)

QDataStream &	operator<< (quint16 i)

QDataStream &	operator<< (quint32 i)

QDataStream &	operator<< (quint64 i)

QDataStream &	operator<< (quint8 i)

QDataStream &	operator<< (unsigned long i)

QDataStream &	operator>> (bool &i)

QDataStream &	operator>> (char *&str)

QDataStream &	operator>> (double &f)

QDataStream &	operator>> (float &f)

QDataStream &	operator>> (long &i)

QDataStream &	operator>> (qint16 &i)

QDataStream &	operator>> (qint32 &i)

QDataStream &	operator>> (qint64 &i)

QDataStream &	operator>> (qint8 &i)

QDataStream &	operator>> (quint16 &i)

QDataStream &	operator>> (quint32 &i)

QDataStream &	operator>> (quint64 &i)

QDataStream &	operator>> (quint8 &i)

QDataStream &	operator>> (unsigned long &i)

QDataStream &	readBytes (char *&buffer, uint &len)

int	readRawData (char *buffer, int len)

void	resetStatus ()

void	setByteOrder (ByteOrder order)

void	setDevice (QIODevice *device)

void	setFloatingPointPrecision (FloatingPointPrecision precision)

void	setStatus (Status status)

void	setVersion (int version)

int	skipRawData (int len)

Status	status () const

int	version () const

QDataStream &	writeBytes (const char *buffer, uint len)

int	writeRawData (const char *buffer, int len)

Related Functions
These are not member functions
QDataStream &	operator<< (QDataStream &stream, const QFlatMap< Key, Val, C > &flatmap)

QDataStream &	operator<< (QDataStream &stream, const QHash< Key, Val, Hash, KeyEqual > &hash)

QDataStream &	operator<< (QDataStream &stream, const QLinkedList< T > &list)

QDataStream &	operator<< (QDataStream &stream, const QList< T > &list)

QDataStream &	operator<< (QDataStream &stream, const QMap< Key, Val, C > &map)

QDataStream &	operator<< (QDataStream &stream, const QMultiHash< Key, Val, Hash, KeyEqual > &hash)

QDataStream &	operator<< (QDataStream &stream, const QMultiMap< Key, Val, C > &map)

QDataStream &	operator<< (QDataStream &stream, const QSet< T > &set)

QDataStream &	operator<< (QDataStream &stream, const QVector< T > &vector)

QDataStream &	operator>> (QDataStream &stream, QFlatMap< Key, Val, C > &flatmap)

QDataStream &	operator>> (QDataStream &stream, QHash< Key, Val, Hash, KeyEqual > &hash)

QDataStream &	operator>> (QDataStream &stream, QLinkedList< T > &list)

QDataStream &	operator>> (QDataStream &stream, QList< T > &list)

QDataStream &	operator>> (QDataStream &stream, QMap< Key, Val, C > &map)

QDataStream &	operator>> (QDataStream &stream, QMultiHash< Key, Val, Hash, KeyEqual > &hash)

QDataStream &	operator>> (QDataStream &stream, QMultiMap< Key, Val, C > &map)

QDataStream &	operator>> (QDataStream &stream, QSet< T > &set)

QDataStream &	operator>> (QDataStream &stream, QVector< T > &vector)

Detailed Description

The QDataStream class provides serialization of binary data to 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 I/O device.

A data stream is a binary stream of encoded information which is 100% independent of the host computer's operating system, CPU or byte order. You can use a data stream to read/write raw unencoded binary data. If you want a text based input stream refer to QTextStream.

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

The following is an example to write binary data to a stream.

QFile file("file.dat");
file.open(QIODevice::WriteOnly);
 
QDataStream out(&file);             // we will serialize the data into the file
out << QString("the answer is");    // serialize a string
out << (qint32)42;                  // serialize an integer

The following is an example to read binary data from a stream.

QFile file("file.dat");
file.open(QIODevice::ReadOnly);
QDataStream in(&file);    // read the data serialized from the file
 
QString str;
qint32 a;
in >> str >> a;           // extract "the answer is" and 42

Each item written to the stream is written in a predefined binary format that varies depending on the item's type. Supported types include QBrush, QColor, QDateTime, QFont, QPixmap, QString, QVariant and many others. For the complete list of supported streaming data types refer to Serializing Data Types.

For integers it is best to always cast to a CopperSpice integer type for writing, and to read back into the same CopperSpice integer type. This ensures that you get integers of the size you want and insulates you from compiler and platform differences.

To take one example, a char * string is written as a 32-bit integer equal to the length of the string including the '\0' byte, followed by all the characters of the string including the '\0' byte. When reading a char * string, 4 bytes are read to create the 32-bit length value, then that many characters for the char * string including the '\0' terminator are read.

The initial I/O device is usually set in the constructor, but can be changed with setDevice(). If you have reached the end of the data (or if there is no I/O device set) atEnd() will return true.

Versioning

When inputting or outputting complex types, it is very important to make sure the same version of the stream (version()) is used for reading and writing. If you need both forward and backward compatibility, you can hardcode the version number in the application:

stream.setVersion(QDataStream::CS_1_7);

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.

QFile file("file.xxx");
file.open(QIODevice::WriteOnly);
QDataStream out(&file);
 
// Write a header with a "magic number" and a version
out << (quint32)0xA0B0C0D0;
out << (qint32)123;
 
out.setVersion(QDataStream::CS_1_7);
 
// Write the data
out << lots_of_interesting_data;

Then read it in with the following code.

 QFile file("file.xxx");
 file.open(QIODevice::ReadOnly);
 QDataStream in(&file);
 
 // Read and check the header
 quint32 magic;
 in >> magic;
 
 if (magic != 0xA0B0C0D0) {
     return XXX_BAD_FILE_FORMAT;
}
 
 // Read the version
 qint32version;
 in >> version;
 
 if (version < 100) {
     return XXX_BAD_FILE_TOO_OLD;
 }
 
 if (version > 123) {
     return XXX_BAD_FILE_TOO_NEW;
 }
 
 if (version <= 110) {
     in.setVersion(QDataStream::CS_1_6);
 } else {
     in.setVersion(QDataStream::CS_1_7);
 }
 
 // read the data
 in >> lots_of_interesting_data;
 
 if (version >= 120) {
     in >> data_new_in_XXX_version_1_2;
 }
 
 in >> other_interesting_data;

You 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.

Raw binary data

Data may be read from a stream into a preallocated char * using readRawData(). In addition, data can be written to a stream using writeRawData(). Any encoding/decoding of the data must be done in your program.

A similar pair of functions is readBytes() and writeBytes(). These differ from their raw counterparts as follows: readBytes() reads a quint32 which is taken to be the length of the data to be read, then that number of bytes is read into the preallocated char *, writeBytes() writes a quint32 containing the length of the data, followed by the data. Any encoding/decoding of the data (apart from the length quint32) must be done in your code.

Containers

The CopperSpice container classes can be written to or read from a QDataStream. These classes include QList, QLinkedList, QVector, QSet, QHash, QMultiMap, QMap, and QMultiMap. Most of the stream operators are functions.

Other Classes

The following is an example of how a non container class supports writing to or reading from a QDataStream. QXxx can be a variety of different classes. Review the QDataStream documentation for a full list.

QDataStream &operator<<(QDataStream &, const QXxx &);

QDataStream &operator>>(QDataStream &, QXxx &);

The following operator functions support reading and writing a QImage.

QDataStream &operator<< (QDataStream & stream, const QImage &image);

QDataStream &operator>> (QDataStream & stream, QImage &image);

See also: QTextStream, QVariant

Member Enumeration Documentation

enum QDataStream::ByteOrder

The byte order used for reading/writing the data.

Constant	Value	Description
`QDataStream::BigEndian`	`QSysInfo::BigEndian`	Most significant byte first (the default)
`QDataStream::LittleEndian`	`QSysInfo::LittleEndian`	Least significant byte first

enum QDataStream::FloatingPointPrecision

The precision of floating point numbers used for reading/writing the data.

Warning: The floating point precision must be set to the same value on the object that writes and the object that reads the data stream.

Constant	Value	Description
`QDataStream::SinglePrecision`	`0`	All floating point numbers in the data stream have 32-bit precision.
`QDataStream::DoublePrecision`	`1`	All floating point numbers in the data stream have 64-bit precision.

See also: setFloatingPointPrecision(), floatingPointPrecision()

enum QDataStream::Status

This enum describes the current status of the data stream.

Constant	Value	Description
`QDataStream::Ok`	`0`	The data stream is operating normally.
`QDataStream::ReadPastEnd`	`1`	The data stream has read past the end of the data in the underlying device.
`QDataStream::ReadCorruptData`	`2`	The data stream has read corrupt data.
`QDataStream::WriteFailed`	`3`	The data stream can not write to the underlying device.

enum QDataStream::Version

This enum provides symbolic synonyms for the data serialization format version numbers.

Constant	Value	Description
`QDataStream::CS_1_0`	`128`	Version 1.0
`QDataStream::CS_1_1`	`128`	Version 1.0
`QDataStream::CS_1_2`	`128`	Version 1.0
`QDataStream::CS_1_3`	`128`	Version 1.0
`QDataStream::CS_1_4`	`128`	Version 1.0
`QDataStream::CS_1_5`	`128`	Version 1.0
`QDataStream::CS_1_6`	`128`	Version 1.0
`QDataStream::CS_1_7`	`128`	Version 1.0

See also: setVersion(), version()

Constructor & Destructor Documentation

QDataStream::QDataStream ( )

Constructs a data stream that has no I/O device.

See also: setDevice()

QDataStream::QDataStream ( QIODevice * device )

explicit

Constructs a data stream that uses the given I/O device.

Warning: If you use QSocket or QSocketDevice as the I/O device d for reading data, you must make sure that enough data is available on the socket for the operation to successfully proceed; QDataStream does not have any means to handle or recover from short-reads.

See also: setDevice(), device()

QDataStream::QDataStream	(	QByteArray *	buffer,
		QIODevice::OpenMode	mode
	)

Constructs a data stream that operates on a byte array buffer. The mode describes how the device is to be used. Alternatively, you can use QDataStream(const QByteArray &) if you just want to read from a byte array.

QDataStream::QDataStream ( const QByteArray & buffer )

Constructs a read only data stream that operates on byte array buffer. Use QDataStream(QByteArray*, int) if you want to write to a byte array.

QDataStream::~QDataStream ( )

virtual

Destroys the data stream.

The destructor will not affect the current I/O device, unless it is an internal I/O device (e.g. a QBuffer) processing a QByteArray passed in the constructor, in which case the internal I/O device is destroyed.

Method Documentation

bool QDataStream::atEnd ( ) const

Returns true if the I/O device has reached the end position (end of the stream or file) or if there is no I/O device set, otherwise returns false.

See also: QIODevice::atEnd()

QDataStream::ByteOrder QDataStream::byteOrder ( ) const

inline

Returns the current byte order setting, either BigEndian or LittleEndian.

See also: setByteOrder()

QIODevice * QDataStream::device ( ) const

inline

Returns the I/O device currently set or a nullptr if no device is currently set.

See also: setDevice()

FloatingPointPrecision QDataStream::floatingPointPrecision ( ) const

Returns the floating point precision of the data stream.

See also: FloatingPointPrecision, setFloatingPointPrecision()

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

Writes a boolean i to the stream and returns a reference to the stream.

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

Writes a null terminated string str to the stream and returns a reference to the stream. The string is serialized using writeBytes().

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

Writes a floating point number f to the stream using the standard IEEE 754 format. Returns a reference to the stream.

See also: setFloatingPointPrecision()

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

Writes a floating point number f to the stream using the standard IEEE 754 format. Returns a reference to the stream.

See also: setFloatingPointPrecision()

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

Writes a long i to the stream and returns a reference to the stream.

QDataStream & QDataStream::operator<< ( qint16 i )

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

QDataStream & QDataStream::operator<< ( qint32 i )

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

QDataStream & QDataStream::operator<< ( qint64 i )

Writes a signed 64-bit integer i to the stream and returns a reference to the stream.

QDataStream & QDataStream::operator<< ( qint8 i )

Writes a signed 8-bit integer i to the stream and returns a reference to the stream.

QDataStream & QDataStream::operator<< ( quint16 i )

inline

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

QDataStream & QDataStream::operator<< ( quint32 i )

inline

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

QDataStream & QDataStream::operator<< ( quint64 i )

inline

Writes an unsigned 64-bit integer i to the stream and returns a reference to the stream.

QDataStream & QDataStream::operator<< ( quint8 i )

inline

Writes an unsigned 8-bit integer i to the stream and returns a reference to the stream.

QDataStream & QDataStream::operator<< ( unsigned long i )

Writes an unsigned long i to the stream and returns a reference to the stream.

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

Reads a boolean from the stream into i and returns a reference to the stream.

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

Reads a null terminated string str from the stream and returns a reference to the stream. Space for the string is allocated using new, the caller must destroy it with delete[].

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

Reads a floating point number from the stream into f using the standard IEEE 754 format. Returns a reference to the stream.

See also: setFloatingPointPrecision()

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

Reads a floating point number from the stream into f using the standard IEEE 754 format. Returns a reference to the stream.

See also: setFloatingPointPrecision()

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

Reads a long from the stream into i and returns a reference to the stream.

QDataStream & QDataStream::operator>> ( qint16 & i )

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

QDataStream & QDataStream::operator>> ( qint32 & i )

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

QDataStream & QDataStream::operator>> ( qint64 & i )

Reads a signed 64-bit integer from the stream into i and returns a reference to the stream.

QDataStream & QDataStream::operator>> ( qint8 & i )

Reads a signed 8-bit integer from the stream into i and returns a reference to the stream.

QDataStream & QDataStream::operator>> ( quint16 & i )

inline

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

QDataStream & QDataStream::operator>> ( quint32 & i )

inline

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

QDataStream & QDataStream::operator>> ( quint64 & i )

inline

Reads an unsigned 64-bit integer from the stream into i and returns a reference to the stream.

QDataStream & QDataStream::operator>> ( quint8 & i )

inline

Reads an unsigned 8-bit integer from the stream into i and returns a reference to the stream.

QDataStream & QDataStream::operator>> ( unsigned long & i )

Reads a unsigned long from the stream into i and returns a reference to the stream.

QDataStream & QDataStream::readBytes	(	char *&	buffer,
		uint &	len
	)

Reads the buffer from the stream and returns a reference to the stream. The buffer s is allocated using new. Destroy it with the delete[] operator.

The len parameter is set to the length of the buffer. If the string read is empty, len is set to 0 and buffer is set to a null pointer. The serialization format is a quint32 length specifier first, then len bytes of data.

See also: readRawData(), writeBytes()

int QDataStream::readRawData	(	char *	buffer,
		int	len
	)

Reads at most len bytes from the stream into s and returns the number of bytes read. If an error occurs, this method returns -1. The buffer s must be preallocated. The data is not encoded.

See also: readBytes(), QIODevice::read(), writeRawData()

void QDataStream::resetStatus ( )

Resets the status of the data stream.

See also: Status, status(), setStatus()

void QDataStream::setByteOrder ( ByteOrder order )

Sets the serialization byte order to order. The order 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 * device )

Sets the I/O device to device which can be nullptr to unset the current I/O device.

See also: device()

void QDataStream::setFloatingPointPrecision ( FloatingPointPrecision precision )

Sets the floating point precision of the data stream to precision.

If the floating point precision is DoublePrecision all floating point numbers will be written and read with 64-bit precision. If the floating point precision is SinglePrecision all floating point numbers will be written and read with 32-bit precision.

The default is DoublePrecision.

Warning: This property must be set to the same value on the object that writes and the object that reads the data stream.

See also: floatingPointPrecision()

void QDataStream::setStatus ( Status status )

Sets the status of the data stream to the status given. Subsequent calls to setStatus() are ignored until resetStatus() is called.

See also: Status, status(), resetStatus()

void QDataStream::setVersion ( int version )

inline

Sets the version number of the data serialization format to version.

To accommodate new functionality the datastream serialization format may change. If you want to read data which was created by an earlier version of CopperSpice or write data which can be read by a program compiled with an earlier version, use this function to modify the serialization format used by QDataStream.

The Version enum provides symbolic constants for the different versions.

QDataStream out(file);

out.setVersion(QDataStream::CS_1_7);

See also: version(), Version

int QDataStream::skipRawData ( int len )

Skips len bytes from the device. Returns the number of bytes actually skipped, or -1 on error. This is equivalent to calling readRawData() on a buffer of length len and ignoring the buffer.

See also: QIODevice::seek()

Status QDataStream::status ( ) const

Returns the status of the data stream.

See also: Status, setStatus(), resetStatus()

int QDataStream::version ( ) const

inline

Returns the version number of the data serialization format.

See also: setVersion(), Version

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

Writes the length specifier len and buffer to the stream and returns a reference to the stream. The len is serialized as a quint32, followed by len bytes from buffer. The data is not encoded.

See also: writeRawData(), readBytes()

int QDataStream::writeRawData	(	const char *	buffer,
		int	len
	)

Writes len bytes from buffer to the stream. Returns the number of bytes actually written, or -1 on error. The data is not encoded.

See also: writeBytes(), QIODevice::write(), readRawData()

Friends And Related Function Documentation

QDataStream & operator<<	(	QDataStream &	stream,
		const QFlatMap< Key, Val, C > &	flatmap
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator<<	(	QDataStream &	stream,
		const QHash< Key, Val, Hash, KeyEqual > &	hash
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator<<	(	QDataStream &	stream,
		const QLinkedList< T > &	list
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator<<	(	QDataStream &	stream,
		const QList< T > &	list
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator<<	(	QDataStream &	stream,
		const QMap< Key, Val, C > &	map
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator<<	(	QDataStream &	stream,
		const QMultiHash< Key, Val, Hash, KeyEqual > &	hash
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator<<	(	QDataStream &	stream,
		const QMultiMap< Key, Val, C > &	map
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator<<	(	QDataStream &	stream,
		const QSet< T > &	set
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator<<	(	QDataStream &	stream,
		const QVector< T > &	vector
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator>>	(	QDataStream &	stream,
		QFlatMap< Key, Val, C > &	flatmap
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator>>	(	QDataStream &	stream,
		QHash< Key, Val, Hash, KeyEqual > &	hash
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator>>	(	QDataStream &	stream,
		QLinkedList< T > &	list
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator>>	(	QDataStream &	stream,
		QList< T > &	list
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator>>	(	QDataStream &	stream,
		QMap< Key, Val, C > &	map
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator>>	(	QDataStream &	stream,
		QMultiHash< Key, Val, Hash, KeyEqual > &	hash
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator>>	(	QDataStream &	stream,
		QMultiMap< Key, Val, C > &	map
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator>>	(	QDataStream &	stream,
		QSet< T > &	set
	)

Refer to Serializing Data Types for additional information.

QDataStream & operator>>	(	QDataStream &	stream,
		QVector< T > &	vector
	)

Refer to Serializing Data Types for additional information.

Public Types

Public Methods

Related Functions

Detailed Description

Versioning

Raw binary data

Containers

Other Classes

Member Enumeration Documentation

Constructor & Destructor Documentation

Method Documentation

Friends And Related Function Documentation