QDataStream Class

QDataStream??類提供的二進制數據的序列化到??QIODevice中。?更多...

Header:	#include <QDataStream>
qmake:	QT += core

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注意：??此類中的所有函數都是??可重入的。

Public Types

enum	ByteOrder?{ BigEndian, LittleEndian }
enum	FloatingPointPrecision?{ SinglePrecision, DoublePrecision }
enum	Status?{ Ok, ReadPastEnd, ReadCorruptData, WriteFailed }
enum	Version?{ Qt_1_0, Qt_2_0, Qt_2_1, Qt_3_0, ..., Qt_5_13 }

Public Functions

?	QDataStream(const QByteArray &a)
?	QDataStream(QByteArray *a, QIODevice::OpenMode?mode)
?	QDataStream(QIODevice *d)
?	QDataStream()
?	~QDataStream()
void	abortTransaction()
bool	atEnd() const
QDataStream::ByteOrder	byteOrder() const
bool	commitTransaction()
QIODevice *	device() const
QDataStream::FloatingPointPrecision	floatingPointPrecision() const
QDataStream &	readBytes(char *&s, uint &l)
int	readRawData(char *s, int?len)
void	resetStatus()
void	rollbackTransaction()
void	setByteOrder(QDataStream::ByteOrder?bo)
void	setDevice(QIODevice *d)
void	setFloatingPointPrecision(QDataStream::FloatingPointPrecision?precision)
void	setStatus(QDataStream::Status?status)
void	setVersion(int?v)
int	skipRawData(int?len)
void	startTransaction()
QDataStream::Status	status() const
int	version() const
QDataStream &	writeBytes(const char *s, uint?len)
int	writeRawData(const char *s, int?len)
QDataStream &	operator<<(qint8?i)
QDataStream &	operator<<(quint8?i)
QDataStream &	operator<<(qint16?i)
QDataStream &	operator<<(quint16?i)
QDataStream &	operator<<(qint32?i)
QDataStream &	operator<<(quint32?i)
QDataStream &	operator<<(qint64?i)
QDataStream &	operator<<(quint64?i)
QDataStream &	operator<<(std::nullptr_t?ptr)
QDataStream &	operator<<(bool?i)
QDataStream &	operator<<(qfloat16?f)
QDataStream &	operator<<(float?f)
QDataStream &	operator<<(double?f)
QDataStream &	operator<<(const char *s)
QDataStream &	operator>>(qint8 &i)
QDataStream &	operator>>(quint8 &i)
QDataStream &	operator>>(qint16 &i)
QDataStream &	operator>>(quint16 &i)
QDataStream &	operator>>(qint32 &i)
QDataStream &	operator>>(quint32 &i)
QDataStream &	operator>>(qint64 &i)
QDataStream &	operator>>(quint64 &i)
QDataStream &	operator>>(std::nullptr_t &ptr)
QDataStream &	operator>>(bool &i)
QDataStream &	operator>>(qfloat16 &f)
QDataStream &	operator>>(float &f)
QDataStream &	operator>>(double &f)
QDataStream &	operator>>(char *&s)

詳細說明

數據流是編碼信息的二進制流，它與主機計算機的操作系統，CPU或字節順序無關，都是100％的。例如，運行Windows的Sun SPARC可以讀取Windows下PC寫入的數據流。

您還可以使用數據流來讀取/寫入未編碼的原始二進制數據。如果要“解析”輸入流，請參見QTextStream。

的QDataStream類實現C ++的基本數據類型，等的串行化char，short，int，char *，更復雜的數據的序列化等由數據分解成原始單元來完成的。

數據流與QIODevice緊密協作。甲QIODevice中表示的輸入/輸出介質中的一種可以讀取數據和寫入數據到。的一個QFile類是一個I / O設備的一個例子。

示例（將二進制數據寫入流）：

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

示例（從流中讀取二進制數據）：

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

寫入流的每個項目均以預定義的二進制格式寫入，該格式根據項目的類型而有所不同。支持Qt的類型包括QBrush，而QColor，QDateTime，QFont，QPixmap的，QString的，的QVariant和其他許多人。有關支持數據流的所有Qt類型的完整列表，請參見序列化Qt數據類型。

對于整數，最好始終將其轉換為Qt整數類型進行寫入，然后再讀回相同的Qt整數類型。這樣可以確保獲得所需大小的整數，并使您與編譯器和平臺的差異隔離。

舉一個例子，一個char *字符串被寫為一個32位整數，該整數等于包括'\ 0'字節的字符串的長度，其后是包括'\ 0'字節的字符串的所有字符。讀取char *字符串時，將讀取4個字節以創建32位長度值，然后讀取該字符串的許多字符，char *包括'\ 0'終止符。

初始I / O設備通常在構造函數中設置，但可以使用setDevice（）進行更改。如果到達數據末尾（或沒有設置I / O設備），則atEnd（）將返回true。

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Member Type Documentation

enum QDataStream::ByteOrder

The byte order used for reading/writing the data.

ConstantValueDescription

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. 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.

ConstantValueDescription

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() and?floatingPointPrecision().

enum QDataStream::Status

This enum describes the current status of the data stream.

ConstantValueDescription

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 cannot write to the underlying device.

enum QDataStream::Version

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

ConstantValueDescription

QDataStream::Qt_1_0	1	Version 1 (Qt 1.x)
QDataStream::Qt_2_0	2	Version 2 (Qt 2.0)
QDataStream::Qt_2_1	3	Version 3 (Qt 2.1, 2.2, 2.3)
QDataStream::Qt_3_0	4	Version 4 (Qt 3.0)
QDataStream::Qt_3_1	5	Version 5 (Qt 3.1, 3.2)
QDataStream::Qt_3_3	6	Version 6 (Qt 3.3)
QDataStream::Qt_4_0	7	Version 7 (Qt 4.0, Qt 4.1)
QDataStream::Qt_4_1	Qt_4_0	Version 7 (Qt 4.0, Qt 4.1)
QDataStream::Qt_4_2	8	Version 8 (Qt 4.2)
QDataStream::Qt_4_3	9	Version 9 (Qt 4.3)
QDataStream::Qt_4_4	10	Version 10 (Qt 4.4)
QDataStream::Qt_4_5	11	Version 11 (Qt 4.5)
QDataStream::Qt_4_6	12	Version 12 (Qt 4.6, Qt 4.7, Qt 4.8)
QDataStream::Qt_4_7	Qt_4_6	Same as Qt_4_6.
QDataStream::Qt_4_8	Qt_4_7	Same as Qt_4_6.
QDataStream::Qt_4_9	Qt_4_8	Same as Qt_4_6.
QDataStream::Qt_5_0	13	Version 13 (Qt 5.0)
QDataStream::Qt_5_1	14	Version 14 (Qt 5.1)
QDataStream::Qt_5_2	15	Version 15 (Qt 5.2)
QDataStream::Qt_5_3	Qt_5_2	Same as Qt_5_2
QDataStream::Qt_5_4	16	Version 16 (Qt 5.4)
QDataStream::Qt_5_5	Qt_5_4	Same as Qt_5_4
QDataStream::Qt_5_6	17	Version 17 (Qt 5.6)
QDataStream::Qt_5_7	Qt_5_6	Same as Qt_5_6
QDataStream::Qt_5_8	Qt_5_7	Same as Qt_5_6
QDataStream::Qt_5_9	Qt_5_8	Same as Qt_5_6
QDataStream::Qt_5_10	Qt_5_9	Same as Qt_5_6
QDataStream::Qt_5_11	Qt_5_10	Same as Qt_5_6
QDataStream::Qt_5_12	18	Version 18 (Qt 5.12)
QDataStream::Qt_5_13	19	Version 19 (Qt 5.13)

See also?setVersion() and?version().

Member Function Documentation

QDataStream::QDataStream(const?QByteArray?&a)

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

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

QDataStream::QDataStream(QByteArray?*a,?QIODevice::OpenMode?mode)

Constructs a data stream that operates on a byte array,?a. 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.

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

QDataStream::QDataStream(QIODevice?*d)

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

See also?setDevice() and?device().

QDataStream::QDataStream()

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

See also?setDevice().

QDataStream::~QDataStream()

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.

void?QDataStream::abortTransaction()

Aborts a read transaction.

This function is commonly used to discard the transaction after higher-level protocol errors or loss of stream synchronization.

If called on an inner transaction, aborting is delegated to the outermost transaction, and subsequently started inner transactions are forced to fail.

For the outermost transaction, discards the restoration point and any internally duplicated data of the stream. Will not affect the current read position of the stream.

Sets the status of the data stream to

ConstantDescription

ReadCorruptData	.

This function was introduced in Qt 5.7.

See also?startTransaction(),?commitTransaction(), and?rollbackTransaction().

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

Returns the current byte order setting -- either?BigEndian?or?LittleEndian.

See also?setByteOrder().

bool?QDataStream::commitTransaction()

Completes a read transaction. Returns?true?if no read errors have occurred during the transaction; otherwise returns?false.

If called on an inner transaction, committing will be postponed until the outermost commitTransaction(),?rollbackTransaction(), or?abortTransaction() call occurs.

Otherwise, if the stream status indicates reading past the end of the data, this function restores the stream data to the point of the?startTransaction() call. When this situation occurs, you need to wait for more data to arrive, after which you start a new transaction. If the data stream has read corrupt data or any of the inner transactions was aborted, this function aborts the transaction.

This function was introduced in Qt 5.7.

See also?startTransaction(),?rollbackTransaction(), and?abortTransaction().

QIODevice?*QDataStream::device() const

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

See also?setDevice().

QDataStream::FloatingPointPrecision?QDataStream::floatingPointPrecision() const

Returns the floating point precision of the data stream.

This function was introduced in Qt 4.6.

See also?FloatingPointPrecision?and?setFloatingPointPrecision().

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.

The?l?parameter is set to the length of the buffer. If the string read is empty,?l?is set to 0 and?s?is set to?nullptr.

The serialization format is a quint32 length specifier first, then?l?bytes of data.

See also?readRawData() and?writeBytes().

int?QDataStream::readRawData(char?*s,?int?len)

Reads at most?len?bytes from the stream into?s?and returns the number of bytes read. If an error occurs, this function returns -1.

The buffer?s?must be preallocated. The data is?not?decoded.

See also?readBytes(),?QIODevice::read(), and?writeRawData().

void?QDataStream::resetStatus()

Resets the status of the data stream.

See also?Status,?status(), and?setStatus().

void?QDataStream::rollbackTransaction()

Reverts a read transaction.

This function is commonly used to rollback the transaction when an incomplete read was detected prior to committing the transaction.

If called on an inner transaction, reverting is delegated to the outermost transaction, and subsequently started inner transactions are forced to fail.

For the outermost transaction, restores the stream data to the point of the?startTransaction() call. If the data stream has read corrupt data or any of the inner transactions was aborted, this function aborts the transaction.

If the preceding stream operations were successful, sets the status of the data stream to

ConstantDescription

ReadPastEnd	.

This function was introduced in Qt 5.7.

See also?startTransaction(),?commitTransaction(), and?abortTransaction().

void?QDataStream::setByteOrder(QDataStream::ByteOrder?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 I/O device to?d, which can be?nullptr?to unset to current I/O device.

See also?device().

void?QDataStream::setFloatingPointPrecision(QDataStream::FloatingPointPrecision?precision)

Sets the floating point precision of the data stream to?precision. If the floating point precision is?DoublePrecision?and the version of the data stream is?Qt_4_6?or higher, all floating point numbers will be written and read with 64-bit precision. If the floating point precision is?SinglePrecision?and the version is?Qt_4_6?or higher, all floating point numbers will be written and read with 32-bit precision.

For versions prior to?Qt_4_6, the precision of floating point numbers in the data stream depends on the stream operator called.

The default is?DoublePrecision.

Note that this property does not affect the serialization or deserialization of?qfloat16?instances.

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

This function was introduced in Qt 4.6.

See also?floatingPointPrecision().

void?QDataStream::setStatus(QDataStream::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(), and?resetStatus().

void?QDataStream::setVersion(int?v)

Sets the version number of the data serialization format to?v, a value of the?Version?enum.

You don't?have?to set a version if you are using the current version of Qt, but for your own custom binary formats we recommend that you do; see?Versioning?in the Detailed Description.

To accommodate 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 used by?QDataStream.

The?Version?enum provides symbolic constants for the different versions of Qt. For example:

QDataStream out(file); out.setVersion(QDataStream::Qt_4_0);

See also?version() and?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.

This function was introduced in Qt 4.1.

See also?QIODevice::seek().

void?QDataStream::startTransaction()

Starts a new read transaction on the stream.

Defines a restorable point within the sequence of read operations. For sequential devices, read data will be duplicated internally to allow recovery in case of incomplete reads. For random-access devices, this function saves the current position of the stream. Call?commitTransaction(),?rollbackTransaction(), or?abortTransaction() to finish the current transaction.

Once a transaction is started, subsequent calls to this function will make the transaction recursive. Inner transactions act as agents of the outermost transaction (i.e., report the status of read operations to the outermost transaction, which can restore the position of the stream).

Note:?Restoring to the point of the nested startTransaction() call is not supported.

When an error occurs during a transaction (including an inner transaction failing), reading from the data stream is suspended (all subsequent read operations return empty/zero values) and subsequent inner transactions are forced to fail. Starting a new outermost transaction recovers from this state. This behavior makes it unnecessary to error-check every read operation separately.

This function was introduced in Qt 5.7.

See also?commitTransaction(),?rollbackTransaction(), and?abortTransaction().

QDataStream::Status?QDataStream::status() const

Returns the status of the data stream.

See also?Status,?setStatus(), and?resetStatus().

int?QDataStream::version() const

Returns the version number of the data serialization format.

See also?setVersion() and?Version.

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 a quint32, followed by?len?bytes from?s. Note that the data is?not?encoded.

See also?writeRawData() and?readBytes().

int?QDataStream::writeRawData(const?char?*s,?int?len)

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

See also?writeBytes(),?QIODevice::write(), and?readRawData().

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

Writes a signed byte,?i, to the stream and returns a reference to the stream.

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

This is an overloaded function.

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

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

This is an overloaded function.

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

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

This is an overloaded function.

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

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

This is an overloaded function.

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

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

This is an overloaded function.

Writes an unsigned integer,?i, to the stream as a 32-bit unsigned integer (quint32). Returns a reference to the stream.

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

This is an overloaded function.

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

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

This is an overloaded function.

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

QDataStream?&QDataStream::operator<<(std::nullptr_t?ptr)

This is an overloaded function.

Simulates writing a?std::nullptr_t,?ptr, to the stream and returns a reference to the stream. This function does not actually write anything to the stream, as?std::nullptr_t?values are stored as 0 bytes.

This function was introduced in Qt 5.9.

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

Writes a boolean value,?i, to the stream. Returns a reference to the stream.

QDataStream?&QDataStream::operator<<(qfloat16?f)

This is an overloaded function.

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

This function was introduced in Qt 5.9.

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

This is an overloaded function.

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<<(double?f)

This is an overloaded function.

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<<(const?char?*s)

This is an overloaded function.

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

The string is serialized using?writeBytes().

See also?writeBytes() and?writeRawData().

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

Reads a signed byte from the stream into?i, and returns a reference to the stream.

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

This is an overloaded function.

Reads an unsigned byte from the stream into?i, and returns a reference to the stream.

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

This is an overloaded function.

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

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

This is an overloaded function.

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

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

This is an overloaded function.

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

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

This is an overloaded function.

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

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

This is an overloaded function.

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

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

This is an overloaded function.

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

QDataStream?&QDataStream::operator>>(std::nullptr_t?&ptr)

This is an overloaded function.

Simulates reading a?std::nullptr_t?from the stream into?ptr?and returns a reference to the stream. This function does not actually read anything from the stream, as?std::nullptr_t?values are stored as 0 bytes.

This function was introduced in Qt 5.9.

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

Reads a boolean value from the stream into?i. Returns a reference to the stream.

QDataStream?&QDataStream::operator>>(qfloat16?&f)

This is an overloaded function.

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

This function was introduced in Qt 5.9.

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

This is an overloaded function.

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>>(double?&f)

This is an overloaded function.

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>>(char?*&s)

This is an overloaded function.

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

The string is deserialized using?readBytes().

Space for the string is allocated using?new []?-- the caller must destroy it with?delete [].

See also?readBytes() and?readRawData().

?

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