TQIODevice Class

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# TQIODevice Class Reference

The TQIODevice class is the base class of I/O devices. More...

All the functions in this class are reentrant when TQt is built with thread support.

`#include <ntqiodevice.h>`

Inherited by TQBuffer, TQFile, TQSocket, and TQSocketDevice.

List of all member functions.

## Public Members

- typedef TQ_ULONG Offset
- TQIODevice ()
- virtual ~TQIODevice ()
- int flags () const
- int mode () const
- int state () const
- bool isDirectAccess () const
- bool isSequentialAccess () const
- bool isCombinedAccess () const
- bool isBuffered () const
- bool isRaw () const
- bool isSynchronous () const
- bool isAsynchronous () const
- bool isTranslated () const
- bool isReadable () const
- bool isWritable () const
- bool isReadWrite () const
- bool isInactive () const
- bool isOpen () const
- int status () const
- void resetStatus ()
- virtual bool open ( int mode ) = 0
- virtual void close () = 0
- virtual void flush () = 0
- virtual Offset size () const = 0
- virtual Offset at () const
- virtual bool at ( Offset pos )
- virtual bool atEnd () const
- bool reset ()
- virtual TQ_LONG readBlock ( char * data, TQ_ULONG maxlen ) = 0
- virtual TQ_LONG writeBlock ( const char * data, TQ_ULONG len ) = 0
- virtual TQ_LONG readLine ( char * data, TQ_ULONG maxlen )
- TQ_LONG writeBlock ( const TQByteArray & data )
- virtual TQByteArray readAll ()
- virtual int getch () = 0
- virtual int putch ( int ch ) = 0
- virtual int ungetch ( int ch ) = 0

## Protected Members

- void setFlags ( int flags )
- void setType ( int type )
- void setMode ( int mode )
- void setState ( int state )
- void setStatus ( int s )

## Detailed Description

The TQIODevice class is the base class of I/O devices.

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

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

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

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

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

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

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

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

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

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

- getch() reads a single character.

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

- putch() writes a single character.

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

- 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.

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

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

The state access are all "get" functions. The TQIODevice 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:

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

- 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().)

- 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.

- CR/LF translation. For simplicity, applications often like to see just a single CR/LF style, and TQIODevice 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().)

- 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().)

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

TQIODevice 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:

        class MyDevice : public TQIODevice
        {
        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 );
        };

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

See also TQDataStream, TQTextStream, and Input/Output and Networking.

## Member Type Documentation

### TQIODevice::Offset

The offset within the device.

## Member Function Documentation

### TQIODevice::TQIODevice ()

Constructs an I/O device.

### TQIODevice::~TQIODevice ()`[virtual]`

Destroys the I/O device.

### Offset TQIODevice::at () const`[virtual]`

Virtual function that returns the current I/O device position.

This is the position of the data read/write head of the I/O device.

See also size().

Example: distributor/distributor.ui.h.

Reimplemented in TQSocket.

### bool TQIODevice::at ( Offset pos )`[virtual]`

Virtual function that sets the I/O device position to pos. Returns true if the position was successfully set, i.e. pos is within range and the seek was successful; otherwise returns false.

See also size().

Reimplemented in TQSocket.

### bool TQIODevice::atEnd () const`[virtual]`

Virtual function that returns true if the I/O device position is at the end of the input; otherwise returns false.

Reimplemented in TQFile and TQSocket.

### void TQIODevice::close ()`[pure virtual]`

Closes the I/O device.

This virtual function must be reimplemented by all subclasses.

See also open().

Example: grapher/grapher.cpp.

Reimplemented in TQFile and TQSocket.

### int TQIODevice::flags () const

Returns the current I/O device flags setting.

Flags consists of mode flags and state flags.

See also mode() and state().

### void TQIODevice::flush ()`[pure virtual]`

Flushes an open I/O device.

This virtual function must be reimplemented by all subclasses.

Reimplemented in TQFile and TQSocket.

### int TQIODevice::getch ()`[pure virtual]`

Reads a single byte/character from the I/O device.

Returns the byte/character read, or -1 if the end of the I/O device has been reached.

This virtual function must be reimplemented by all subclasses.

See also putch() and ungetch().

Reimplemented in TQFile and TQSocket.

### bool TQIODevice::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.

See also isSynchronous().

### bool TQIODevice::isBuffered () const

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

See also isRaw().

### bool TQIODevice::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.

### bool TQIODevice::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.

See also isSequentialAccess().

### bool TQIODevice::isInactive () const

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

See also isOpen().

### bool TQIODevice::isOpen () const

Returns true if the I/O device has been opened; otherwise returns false.

See also isInactive().

Example: network/networkprotocol/nntp.cpp.

### bool TQIODevice::isRaw () const

Returns true if the device is a raw device; otherwise returns false, i.e. if the device is a buffered device.

See also isBuffered().

### bool TQIODevice::isReadWrite () const

Returns true if the I/O device was opened using IO_ReadWrite mode; otherwise returns false.

See also isReadable() and isWritable().

### bool TQIODevice::isReadable () const

Returns true if the I/O device was opened using IO_ReadOnly or IO_ReadWrite mode; otherwise returns false.

See also isWritable() and isReadWrite().

### bool TQIODevice::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.

See also isDirectAccess().

### bool TQIODevice::isSynchronous () const

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

See also isAsynchronous().

### bool TQIODevice::isTranslated () const

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

A TQFile is translated if it is opened with the IO_Translate mode flag.

### bool TQIODevice::isWritable () const

Returns true if the I/O device was opened using IO_WriteOnly or IO_ReadWrite mode; otherwise returns false.

See also isReadable() and isReadWrite().

### int TQIODevice::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 IO_ReadOnly, IO_WriteOnly, IO_ReadWrite, IO_Append, IO_Truncate and IO_Translate.

### bool TQIODevice::open ( int mode )`[pure virtual]`

Opens the I/O device using the specified mode. Returns true if the device was successfully opened; otherwise returns false.

The mode parameter mode must be an OR'ed combination of the following flags.

Mode flags | Meaning
--- | ---
IO_Raw | specifies raw (unbuffered) file access.
IO_ReadOnly | opens a file in read-only mode.
IO_WriteOnly | opens a file in write-only mode.
IO_ReadWrite | opens a file in read/write mode.
IO_Append | sets the file index to the end of the file.
IO_Truncate | truncates the file.
IO_Translate | enables carriage returns and linefeed translation for text files under MS-DOS, Windows and Macintosh. On Unix systems this flag has no effect. Use with caution as it will also transform every linefeed written to the file into a CRLF pair. This is likely to corrupt your file if you write write binary data. Cannot be combined with IO_Raw.

This virtual function must be reimplemented by all subclasses.

See also close().

Example: grapher/grapher.cpp.

Reimplemented in TQFile and TQSocket.

### int TQIODevice::putch ( int ch )`[pure virtual]`

Writes the character ch to the I/O device.

Returns ch, or -1 if an error occurred.

This virtual function must be reimplemented by all subclasses.

See also getch() and ungetch().

Example: grapher/grapher.cpp.

Reimplemented in TQFile and TQSocket.

### TQByteArray TQIODevice::readAll ()`[virtual]`

This convenience function returns all of the remaining data in the device.

### TQ_LONG TQIODevice::readBlock ( char * data, TQ_ULONG maxlen )`[pure virtual]`

Reads at most maxlen bytes from the I/O device into data and returns the number of bytes actually read.

This function should return -1 if a fatal error occurs and should return 0 if there are no bytes to read.

The device must be opened for reading, and data must not be 0.

This virtual function must be reimplemented by all subclasses.

See also writeBlock(), isOpen(), and isReadable().

Example: distributor/distributor.ui.h.

Reimplemented in TQSocket and TQSocketDevice.

### TQ_LONG TQIODevice::readLine ( char * data, TQ_ULONG maxlen )`[virtual]`

Reads a line of text, (or up to maxlen bytes if a newline isn't encountered) plus a terminating '\0' into data. If there is a newline at the end if the line, it is not stripped.

Returns the number of bytes read including the terminating '\0', or -1 if an error occurred.

This virtual function can be reimplemented much more efficiently by the most subclasses.

See also readBlock() and TQTextStream::readLine().

Reimplemented in TQFile.

### bool TQIODevice::reset ()

Sets the device index position to 0.

See also at().

### void TQIODevice::resetStatus ()

Sets the I/O device status to IO_Ok.

See also status().

### void TQIODevice::setFlags ( int flags )`[protected]`

Used by subclasses to set the device flags to the flags specified.

### void TQIODevice::setMode ( int mode )`[protected]`

Used by subclasses to set the device mode to the mode specified.

### void TQIODevice::setState ( int state )`[protected]`

Used by subclasses to set the device state to the state specified.

### void TQIODevice::setStatus ( int s )`[protected]`

Used by subclasses to set the device status (not state) to s.

### void TQIODevice::setType ( int type )`[protected]`

Used by subclasses to set the device type to the type specified.

### Offset TQIODevice::size () const`[pure virtual]`

Virtual function that returns the size of the I/O device.

See also at().

Reimplemented in TQFile and TQSocket.

### int TQIODevice::state () const

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

The flags are: `IO_Open`.

Subclasses may define additional flags.

### int TQIODevice::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.

The status codes are:

Status code | Meaning
--- | ---
IO_Ok | The operation was successful.
IO_ReadError | Could not read from the device.
IO_WriteError | Could not write to the device.
IO_FatalError | A fatal unrecoverable error occurred.
IO_OpenError | Could not open the device.
IO_ConnectError | Could not connect to the device.
IO_AbortError | The operation was unexpectedly aborted.
IO_TimeOutError | The operation timed out.
IO_UnspecifiedError | An unspecified error happened on close.

See also resetStatus().

### int TQIODevice::ungetch ( int ch )`[pure virtual]`

Puts the character ch back into the I/O device and decrements the index position if it is not zero.

This function is normally called to "undo" a getch() operation.

Returns ch, or -1 if an error occurred.

This virtual function must be reimplemented by all subclasses.

See also getch() and putch().

Reimplemented in TQFile and TQSocket.

### TQ_LONG TQIODevice::writeBlock ( const char * data, TQ_ULONG len )`[pure virtual]`

Writes len bytes from data to the I/O device and returns the number of bytes actually written.

This function should return -1 if a fatal error occurs.

This virtual function must be reimplemented by all subclasses.

See also readBlock().

Example: distributor/distributor.ui.h.

Reimplemented in TQBuffer, TQSocket, and TQSocketDevice.

### TQ_LONG TQIODevice::writeBlock ( const TQByteArray & data )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

This convenience function is the same as calling writeBlock( data.data(), data.size() ).

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