QDataStream¶

Inheritance diagram of QDataStream

Synopsis¶

Functions¶

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def __rshift__ (, arg__2)
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def __rshift__ (, history)
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def atEnd ()
def byteOrder ()
def device ()
def floatingPointPrecision ()
def readBool ()
def readDouble ()
def readFloat ()
def readInt16 ()
def readInt32 ()
def readInt64 ()
def readInt8 ()
def readQChar ()
def readQString ()
def readQStringList ()
def readQVariant ()
def readRawData (, len)
def readString ()
def readUInt16 ()
def readUInt32 ()
def readUInt64 ()
def readUInt8 ()
def resetStatus ()
def setByteOrder (arg__1)
def setDevice (arg__1)
def setFloatingPointPrecision (precision)
def setStatus (status)
def setVersion (arg__1)
def skipRawData (len)
def status ()
def unsetDevice ()
def version ()
def writeBool (arg__1)
def writeDouble (arg__1)
def writeFloat (arg__1)
def writeInt16 (arg__1)
def writeInt32 (arg__1)
def writeInt64 (arg__1)
def writeInt8 (arg__1)
def writeQChar (arg__1)
def writeQString (arg__1)
def writeQStringList (arg__1)
def writeQVariant (arg__1)
def writeRawData (arg__1)
def writeString (arg__1)
def writeUInt16 (arg__1)
def writeUInt32 (arg__1)
def writeUInt64 (arg__1)
def writeUInt8 (arg__1)

Detailed Description¶

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

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. For example, a data stream that is written by a PC under Windows can be read by a Sun SPARC running Solaris.

You can also use a data stream to read/write raw unencoded binary data . If you want a “parsing” input stream, see PySide.QtCore.QTextStream .

The PySide.QtCore.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.

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

Example (write binary data to a stream):
file_ = QFile("file.dat")
file_.open(QIODevice.WriteOnly)
# we will serialize the data into the file
out = QDataStream(file_)
# serialize a string
out.writeQString("the answer is")
# serialize an integer
out.writeInt32(42)
Example (read binary data from a stream):
file_ = QFile("file.dat")
file_.open(QIODevice.ReadOnly)
# read the data serialized from the file
i = QDataStream(file_)
string = ''
a = 0
# extract "the answer is" and 42
string = i.readQString()
a = i.readInt32()
Each item written to the stream is written in a predefined binary format that varies depending on the item’s type. Supported Qt types include PySide.QtGui.QBrush , PySide.QtGui.QColor , PySide.QtCore.QDateTime , PySide.QtGui.QFont , PySide.QtGui.QPixmap , PySide.QtCore.QString , PySide.QtCore.QVariant and many others. For the complete list of all Qt types supporting data streaming see Serializing Qt Data Types .

For integers it is best to always cast to a Qt integer type for writing, and to read back into the same Qt 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 PySide.QtCore.QDataStream.setDevice() . If you’ve reached the end of the data (or if there is no I/O device set) PySide.QtCore.QDataStream.atEnd() will return true.

Versioning¶

PySide.QtCore.QDataStream ‘s binary format has evolved since Qt 1.0, and is likely to continue evolving to reflect changes done in Qt. When inputting or outputting complex types, it’s very important to make sure that the same version of the stream ( PySide.QtCore.QDataStream.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.Qt_4_0)
If you are producing a new binary data format, such as a file format for documents created by your application, you could use a PySide.QtCore.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:
file_ = QFile("file.xxx")
file_.open(QIODevice.WriteOnly)
out = QDataStream(file_)

# Write a header with a "magic number" and a version
out.writeInt32(0xA0B0C0D0)
out.writeInt32(123)

out.setVersion(QDataStream.Qt_4_0)

// Write the data
out << lots_of_interesting_data
Then read it in with:
file_ = QFile("file.xxx")
file_.open(QIODevice.ReadOnly)
i = QDataStream(file_)

// Read and check the header
magic = i.readInt32()
if magic != 0xA0B0C0D0:
    return XXX_BAD_FILE_FORMAT

// Read the version
version = i.readInt32()
if version < 100:
    return XXX_BAD_FILE_TOO_OLD
if version > 123:
    return XXX_BAD_FILE_TOO_NEW

if version <= 110:
    in_.setVersion(QDataStream.Qt_3_2)
else:
    in_.setVersion(QDataStream.Qt_4_0)

// 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.

Reading and writing raw binary data¶

You may wish to read/write your own raw binary data to/from the data stream directly. Data may be read from the stream into a preallocated char * using PySide.QtCore.QDataStream.readRawData() . Similarly data can be written to the stream using PySide.QtCore.QDataStream.writeRawData() . Note that any encoding/decoding of the data must be done by you.

A similar pair of functions is PySide.QtCore.QDataStream.readBytes() and PySide.QtCore.QDataStream.writeBytes() . These differ from their raw counterparts as follows: PySide.QtCore.QDataStream.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 * ; PySide.QtCore.QDataStream.writeBytes() writes a quint32 containing the length of the data, followed by the data. Note that any encoding/decoding of the data (apart from the length quint32) must be done by you.

Reading and writing Qt collection classes¶

The Qt container classes can also be serialized to a PySide.QtCore.QDataStream . These include QList , QLinkedList , QVector , QSet , QHash , and QMap . The stream operators are declared as non-members of the classes.

Reading and writing other Qt classes.¶

In addition to the overloaded stream operators documented here, any Qt classes that you might want to serialize to a PySide.QtCore.QDataStream will have appropriate stream operators declared as non-member of the class:
QDataStream &operator<<(QDataStream &, const QXxx &);
QDataStream &operator>>(QDataStream &, QXxx &);
For example, here are the stream operators declared as non-members of the PySide.QtGui.QImage class:
QDataStream & operator<< (QDataStream& stream, const QImage& image);
QDataStream & operator>> (QDataStream& stream, QImage& image);
To see if your favorite Qt class has similar stream operators defined, check the Related Non-Members section of the class’s documentation page.

See also

PySide.QtCore.QTextStream PySide.QtCore.QVariant

class PySide.QtCore.QDataStream¶

class PySide.QtCore.QDataStream(arg__1, flags)

class PySide.QtCore.QDataStream(arg__1)

Parameters:	flags – `PySide.QtCore.QIODevice.OpenMode` arg__1 – `PySide.QtCore.QByteArray`

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

See also

PySide.QtCore.QDataStream.setDevice()

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

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; PySide.QtCore.QDataStream does not have any means to handle or recover from short-reads.

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

Since PySide.QtCore.QByteArray is not a PySide.QtCore.QIODevice subclass, internally a PySide.QtCore.QBuffer is created to wrap the byte array.

PySide.QtCore.QDataStream.ByteOrder¶

The byte order used for reading/writing the data.

Constant	Description
QDataStream.BigEndian	Most significant byte first (the default)
QDataStream.LittleEndian	Least significant byte first

PySide.QtCore.QDataStream.FloatingPointPrecision¶

The precision of floating point numbers used for reading/writing the data. This will only have an effect if the version of the data stream is Qt_4_6 or higher.

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	Description
QDataStream.SinglePrecision	All floating point numbers in the data stream have 32-bit precision.
QDataStream.DoublePrecision	All floating point numbers in the data stream have 64-bit precision.

Note

This enum was introduced or modified in Qt 4.6

PySide.QtCore.QDataStream.Version¶

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

Constant	Description
QDataStream.Qt_1_0	Version 1 (Qt 1.x)
QDataStream.Qt_2_0	Version 2 (Qt 2.0)
QDataStream.Qt_2_1	Version 3 (Qt 2.1, 2.2, 2.3)
QDataStream.Qt_3_0	Version 4 (Qt 3.0)
QDataStream.Qt_3_1	Version 5 (Qt 3.1, 3.2)
QDataStream.Qt_3_3	Version 6 (Qt 3.3)
QDataStream.Qt_4_0	Version 7 (Qt 4.0, Qt 4.1)
QDataStream.Qt_4_1	Version 7 (Qt 4.0, Qt 4.1)
QDataStream.Qt_4_2	Version 8 (Qt 4.2)
QDataStream.Qt_4_3	Version 9 (Qt 4.3)
QDataStream.Qt_4_4	Version 10 (Qt 4.4)
QDataStream.Qt_4_5	Version 11 (Qt 4.5)
QDataStream.Qt_4_6	Version 12 (Qt 4.6)
QDataStream.Qt_4_7	Same as `Qt_4_6` .

PySide.QtCore.QDataStream.Status¶

This enum describes the current status of the data stream.

Constant	Description
QDataStream.Ok	The data stream is operating normally.
QDataStream.ReadPastEnd	The data stream has read past the end of the data in the underlying device.
QDataStream.ReadCorruptData	The data stream has read corrupt data.

PySide.QtCore.QDataStream.atEnd()¶

Return type:	`PySide.QtCore.bool`

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()

PySide.QtCore.QDataStream.byteOrder()¶

Return type:	`PySide.QtCore.QDataStream.ByteOrder`

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

PySide.QtCore.QDataStream.device()¶

Return type:	`PySide.QtCore.QIODevice`

Returns the I/O device currently set, or 0 if no device is currently set.

See also

PySide.QtCore.QDataStream.setDevice()

PySide.QtCore.QDataStream.floatingPointPrecision()¶

Return type:	`PySide.QtCore.QDataStream.FloatingPointPrecision`

Returns the floating point precision of the data stream.

See also

QDataStream.FloatingPointPrecision PySide.QtCore.QDataStream.setFloatingPointPrecision()

PySide.QtCore.QDataStream.__lshift__(item)¶

Parameters:	item – `PySide.QtGui.QTableWidgetItem`
Return type:	`PySide.QtCore.QDataStream`