qiodevice.cpp

Trolltech公司发布的图形界面操作系统。可在qt-embedded-2.3.10平台上编译为嵌入式图形界面操作系统。

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#include "qiodevice.h"

/*!
    \class QIODevice qiodevice.h
    \reentrant

    \brief The QIODevice class is the base class of I/O devices.

    \ingroup io

    An I/O device represents a medium that one can read bytes from
    and/or write bytes to. The QIODevice class is the abstract
    superclass of all such devices; classes such as QFile, QBuffer and
    QSocket inherit QIODevice and implement virtual functions such as
    write() appropriately.

    Although applications sometimes use QIODevice directly, it is
    usually better to use QTextStream and QDataStream, which provide
    stream operations on any QIODevice subclass. QTextStream provides
    text-oriented stream functionality (for human-readable ASCII
    files, for example), whereas QDataStream deals with binary data in
    a totally platform-independent manner.

    The public member functions in QIODevice roughly fall into two
    groups: the action functions and the state access functions. The
    most important action functions are:

    \list

    \i  open() opens a device for reading and/or writing, depending on
    the mode argument.

    \i  close() closes the device and tidies up (e.g. flushes buffered
    data)

    \i  readBlock() reads a block of data from the device.

    \i  writeBlock() writes a block of data to the device.

    \i  readLine() reads a line (of text, usually) from the device.

    \i  flush() ensures that all buffered data are written to the real device.

    \endlist

    There are also some other, less used, action functions:

    \list

    \i  getch() reads a single character.

    \i  ungetch() forgets the last call to getch(), if possible.

    \i  putch() writes a single character.

    \i  size() returns the size of the device, if there is one.

    \i  at() returns the current read/write pointer's position, if there
    is one for this device, or it moves the pointer if given an offset.

    \i  atEnd() indicates whether there is more to read, if this is
    meaningful for this device.

    \i  reset() moves the read/write pointer to the start of the
    device, if that is possible for this device.

    \endlist

    The state access are all "get" functions. The QIODevice subclass
    calls setState() to update the state, and simple access functions
    tell the user of the device what the device's state is. Here are
    the settings, and their associated access functions:

    \list

    \i  Access type. Some devices are direct access (it is possible
    to read/write anywhere), whereas others are sequential. QIODevice
    provides the access functions (isDirectAccess(),
    isSequentialAccess(), and isCombinedAccess()) to tell users what a
    given I/O device supports.

    \i  Buffering. Some devices are accessed in raw mode, whereas
    others are buffered. Buffering usually provides greater
    efficiency, particularly for small read/write operations.
    isBuffered() tells the user whether a given device is buffered.
    (This can often be set by the application in the call to open().)

    \i  Synchronicity. Synchronous devices work immediately (for
    example, files). When you read from a file, the file delivers its
    data straight away. Other kinds of device, such as a socket
    connected to a HTTP server, may not deliver the data until seconds
    after you ask to read it. isSynchronous() and isAsynchronous()
    tell the user how this device operates.

    \i  CR/LF translation. For simplicity, applications often like to
    see just a single CR/LF style, and QIODevice subclasses can
    provide this. isTranslated() returns TRUE if this object
    translates CR/LF to just LF. (This can often be set by the
    application in the call to open().)

    \i  Permissions. Some files cannot be written. For example,
    isReadable(), isWritable() and isReadWrite() tell the application
    whether it can read from and write to a given device. (This can
    often be set by the application in the call to open().)

    \i  Finally, isOpen() returns TRUE if the device is open, i.e.
    after an open() call.

    \endlist

    QIODevice provides numerous pure virtual functions that you need
    to implement when subclassing it. Here is a skeleton subclass with
    all the members you are sure to need and some that you will
    probably need:

    \code
    class MyDevice : public QIODevice
    {
    public:
	MyDevice();
	~MyDevice();

	bool open( int mode );
	void close();
	void flush();

	uint size() const;
	int  at() const;	// non-pure virtual
	bool at( int );		// non-pure virtual
	bool atEnd() const;	// non-pure virtual

	int readBlock( char *data, uint maxlen );
	int writeBlock( const char *data, uint len );
	int readLine( char *data, uint maxlen );

	int getch();
	int putch( int );
	int ungetch( int );
    };
    \endcode

    The three non-pure virtual functions need not be reimplemented for
    sequential devices.

    \sa QDataStream, QTextStream
*/

/*!
    \enum QIODevice::Offset

    The offset within the device.
*/


/*!
    Constructs an I/O device.
*/

QIODevice::QIODevice()
{
    ioMode = 0;					// initial mode
    ioSt = IO_Ok;
    ioIndex = 0;
}

/*!
    Destroys the I/O device.
*/

QIODevice::~QIODevice()
{
}


/*!
    \fn int QIODevice::flags() const

    Returns the current I/O device flags setting.

    Flags consists of mode flags and state flags.

    \sa mode(), state()
*/

/*!
    \fn int QIODevice::mode() const

    Returns bits OR'ed together that specify the current operation
    mode.

    These are the flags that were given to the open() function.

    The flags are \c IO_ReadOnly, \c IO_WriteOnly, \c IO_ReadWrite,
    \c IO_Append, \c IO_Truncate and \c IO_Translate.
*/

/*!
    \fn int QIODevice::state() const

    Returns bits OR'ed together that specify the current state.

    The flags are: \c IO_Open.

    Subclasses may define additional flags.
*/

/*!
    \fn bool QIODevice::isDirectAccess() const

    Returns TRUE if the I/O device is a direct access device;
    otherwise returns FALSE, i.e. if the device is a sequential access
    device.

    \sa isSequentialAccess()
*/

/*!
    \fn bool QIODevice::isSequentialAccess() const

    Returns TRUE if the device is a sequential access device;
    otherwise returns FALSE, i.e. if the device is a direct access
    device.

    Operations involving size() and at(int) are not valid on
    sequential devices.

    \sa isDirectAccess()
*/

/*!
    \fn bool QIODevice::isCombinedAccess() const

    Returns TRUE if the I/O device is a combined access (both direct
    and sequential) device; otherwise returns FALSE.

    This access method is currently not in use.
*/

/*!
    \fn bool QIODevice::isBuffered() const

    Returns TRUE if the I/O device is a buffered device; otherwise
    returns FALSE, i.e. the device is a raw device.

    \sa isRaw()
*/

/*!
    \fn bool QIODevice::isRaw() const

    Returns TRUE if the device is a raw device; otherwise returns
    FALSE, i.e. if the device is a buffered device.

    \sa isBuffered()
*/

/*!
    \fn bool QIODevice::isSynchronous() const

    Returns TRUE if the I/O device is a synchronous device; otherwise
    returns FALSE, i.e. the device is an asynchronous device.

    \sa isAsynchronous()
*/

/*!
    \fn bool QIODevice::isAsynchronous() const

    Returns TRUE if the device is an asynchronous device; otherwise
    returns FALSE, i.e. if the device is a synchronous device.

    This mode is currently not in use.

    \sa isSynchronous()
*/

/*!
    \fn bool QIODevice::isTranslated() const

    Returns TRUE if the I/O device translates carriage-return and
    linefeed characters; otherwise returns FALSE.

    A QFile is translated if it is opened with the \c IO_Translate
    mode flag.
*/

/*!
    \fn bool QIODevice::isReadable() const

    Returns TRUE if the I/O device was opened using \c IO_ReadOnly or
    \c IO_ReadWrite mode; otherwise returns FALSE.

    \sa isWritable(), isReadWrite()
*/

/*!
    \fn bool QIODevice::isWritable() const

    Returns TRUE if the I/O device was opened using \c IO_WriteOnly or
    \c IO_ReadWrite mode; otherwise returns FALSE.

    \sa isReadable(), isReadWrite()
*/

/*!
    \fn bool QIODevice::isReadWrite() const

    Returns TRUE if the I/O device was opened using \c IO_ReadWrite
    mode; otherwise returns FALSE.

    \sa isReadable(), isWritable()
*/

/*!
    \fn bool QIODevice::isInactive() const

    Returns TRUE if the I/O device state is 0, i.e. the device is not
    open; otherwise returns FALSE.

    \sa isOpen()
*/

/*!
    \fn bool QIODevice::isOpen() const

    Returns TRUE if the I/O device has been opened; otherwise returns
    FALSE.

    \sa isInactive()
*/


/*!
    \fn int QIODevice::status() const

    Returns the I/O device status.

    The I/O device status returns an error code. If open() returns
    FALSE or readBlock() or writeBlock() return -1, this function can
    be called to find out the reason why the operation failed.

    \keyword IO_Ok