qdatastream.cpp

奇趣公司比较新的qt/emd版本

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#include "qdatastream.h"

#ifndef QT_NO_DATASTREAM
#include "qbuffer.h"
#include "qstring.h"
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>

/*!
    \class QDataStream
    \reentrant
    \brief The QDataStream class provides serialization of binary data
    to a QIODevice.

    \ingroup io
    \mainclass

    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 \l{raw}{raw
    unencoded binary data}. If you want a "parsing" input stream, see
    QTextStream.

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

    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 I/O device.

    Example (write binary data to a stream):

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

    Example (read binary data from a stream):

    \code
        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
    \endcode

    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 QBrush, QColor, QDateTime, QFont, QPixmap, QString,
    QVariant and many others. For the complete list of all Qt types
    supporting data streaming see the \l{Format of the QDataStream
    operators}.

    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 \c{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 \c{char *} string, 4 bytes are read to
    create the 32-bit length value, then that many characters for the
    \c {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've reached the end of the data
    (or if there is no I/O device set) atEnd() will return true.

    \section1 Versioning

    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 (version()) is used
    for reading and writing. If you need both forward and backward
    compatibility, you can hardcode the version number in the
    application:

    \code
        stream.setVersion(QDataStream::Qt_4_0);
    \endcode

    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:

    \code
        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::Qt_4_0);

        // Write the data
        out << lots_of_interesting_data;
    \endcode

    Then read it in with:

    \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
        qint32 version;
        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::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;
    \endcode

    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.

    \target raw
    \section1 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 \c{char *} using readRawData(). Similarly data can be
    written to the stream using writeRawData(). Note that any
    encoding/decoding of the data must be done by you.

    A similar pair of functions is readBytes() and writeBytes(). These
    differ from their \e 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
    \c{char *}; 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.

    \sa QTextStream QVariant
*/

/*!
    \enum QDataStream::ByteOrder

    The byte order used for reading/writing the data.

    \value BigEndian Most significant byte first (the default)
    \value LittleEndian Less significant byte first
*/

/*!
    \enum QDataStream::Status

    This enum describes the current status of the data stream.

    \value Ok               The data stream is operating normally.
    \value ReadPastEnd      The data stream has read past the end of the
                            data in the underlying device.
    \value ReadCorruptData  The data stream has read corrupt data.
*/

/*****************************************************************************
  QDataStream member functions
 *****************************************************************************/

#undef  CHECK_STREAM_PRECOND
#ifndef QT_NO_DEBUG
#define CHECK_STREAM_PRECOND(retVal) \
    if (!dev) { \
        qWarning("QDataStream: No device"); \
        return retVal; \
    }
#else
#define CHECK_STREAM_PRECOND(retVal) \
    if (!dev) { \
        return retVal; \
    }
#endif

enum {
    DefaultStreamVersion = QDataStream::Qt_4_3
};

// ### 4.0: when streaming invalid QVariants, just the type should
// be written, no "data" after it

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

    \sa setDevice()
*/

QDataStream::QDataStream()
{
    dev = 0;
    owndev = false;
    byteorder = BigEndian;
    ver = DefaultStreamVersion;
    noswap = QSysInfo::ByteOrder == QSysInfo::BigEndian;
    q_status = Ok;
}

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

    \warning If you use QSocket or QSocketDevice as the I/O device \a 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.

    \sa setDevice(), device()
*/

QDataStream::QDataStream(QIODevice *d)
{
    dev = d;                                // set device
    owndev = false;
    byteorder = BigEndian;                        // default byte order
    ver = DefaultStreamVersion;
    noswap = QSysInfo::ByteOrder == QSysInfo::BigEndian;
    q_status = Ok;
}

#ifdef QT3_SUPPORT
/*!
    \fn QDataStream::QDataStream(QByteArray *array, int mode)
    \compat

    Constructs a data stream that operates on the given \a array. The
    \a mode specifies how the byte array is to be used, and is
    usually either QIODevice::ReadOnly or QIODevice::WriteOnly.
*/
QDataStream::QDataStream(QByteArray *a, int mode)
{
    QBuffer *buf = new QBuffer(a);
    buf->open(QIODevice::OpenMode(mode));
    dev = buf;
    owndev = true;
    byteorder = BigEndian;
    ver = DefaultStreamVersion;
    noswap = QSysInfo::ByteOrder == QSysInfo::BigEndian;
    q_status = Ok;
}
#endif

/*!
    \fn QDataStream::QDataStream(QByteArray *a, QIODevice::OpenMode mode)

    Constructs a data stream that operates on a byte array, \a a. The
    \a 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(QByteArray *a, QIODevice::OpenMode flags)
{
    QBuffer *buf = new QBuffer(a);
    buf->open(flags);
    dev = buf;
    owndev = true;
    byteorder = BigEndian;
    ver = DefaultStreamVersion;
    noswap = QSysInfo::ByteOrder == QSysInfo::BigEndian;
    q_status = Ok;
}

/*!
    Constructs a read-only data stream that operates on byte array \a 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(const QByteArray &a)
{
    QBuffer *buf = new QBuffer;
    buf->setData(a);
    buf->open(QIODevice::ReadOnly);
    dev = buf;
    owndev = true;
    byteorder = BigEndian;
    ver = DefaultStreamVersion;
    noswap = QSysInfo::ByteOrder == QSysInfo::BigEndian;
    q_status = Ok;
}

/*!
    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 \e constructor, in which case the internal I/O device
    is destroyed.
*/

QDataStream::~QDataStream()
{
    if (owndev)
        delete dev;
}


/*!
    \fn QIODevice *QDataStream::device() const

    Returns the I/O device currently set.

    \sa setDevice(), unsetDevice()
*/

/*!
    void QDataStream::setDevice(QIODevice *d)

    Sets the I/O device to \a d.

    \sa device(), unsetDevice()
*/

void QDataStream::setDevice(QIODevice *d)
{
    if (owndev) {
        delete dev;
        owndev = false;
    }
    dev = d;
}

/*!
    Unsets the I/O device. This is the same as calling setDevice(0).

    \sa device(), setDevice()
*/

void QDataStream::unsetDevice()
{
    setDevice(0);
}


/*!
    \fn 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.

    \sa QIODevice::atEnd()
*/