QIODevice Class Reference

Constructs a QIODevice object.

Constructs a QIODevice object with the given parent.

The destructor is virtual, and QIODevice is an abstract base class. This destructor does not call close(), but the subclass destructor might. If you are in doubt, call close() before destroying the QIODevice.

Returns true if the current read and write position is at the end of the device (i.e. there is no more data available for reading on the device); otherwise returns false.

For some devices, atEnd() can return true even though there is more data to read. This special case only applies to devices that generate data in direct response to you calling read() (e.g., /dev or /proc files on Unix and Mac OS X, or console input / stdin on all platforms).

See also bytesAvailable(), read(), and isSequential().

Returns the number of bytes that are available for reading. This function is commonly used with sequential devices to determine the number of bytes to allocate in a buffer before reading.

Subclasses that reimplement this function must call the base implementation in order to include the size of QIODevices' buffer. Example:

See also bytesToWrite(), readyRead(), and isSequential().

For buffered devices, this function returns the number of bytes waiting to be written. For devices with no buffer, this function returns 0.

See also bytesAvailable(), bytesWritten(), and isSequential().

Returns true if a complete line of data can be read from the device; otherwise returns false.

Note that unbuffered devices, which have no way of determining what can be read, always return false.

This function is often called in conjunction with the readyRead() signal.

Subclasses that reimplement this function must call the base implementation in order to include the contents of the QIODevice's buffer. Example:

See also readyRead() and readLine().

First emits aboutToClose(), then closes the device and sets its OpenMode to NotOpen. The error string is also reset.

See also setOpenMode() and OpenMode.

Returns a human-readable description of the last device error that occurred.

See also setErrorString().

Reads one character from the device and stores it in c. If c is 0, the character is discarded. Returns true on success; otherwise returns false.

See also read(), putChar(), and ungetChar().

Returns true if the device is open; otherwise returns false. A device is open if it can be read from and/or written to. By default, this function returns false if openMode() returns NotOpen.

See also openMode() and OpenMode.

Returns true if data can be read from the device; otherwise returns false. Use bytesAvailable() to determine how many bytes can be read.

This is a convenience function which checks if the OpenMode of the device contains the ReadOnly flag.

See also openMode() and OpenMode.

Returns true if this device is sequential; otherwise returns false.

Sequential devices, as opposed to a random-access devices, have no concept of a start, an end, a size, or a current position, and they do not support seeking. You can only read from the device when it reports that data is available. The most common example of a sequential device is a network socket. On Unix, special files such as /dev/zero and fifo pipes are sequential.

Regular files, on the other hand, do support random access. They have both a size and a current position, and they also support seeking backwards and forwards in the data stream. Regular files are non-sequential.

See also bytesAvailable().

Returns true if the Text flag is enabled; otherwise returns false.

See also setTextModeEnabled().

Returns true if data can be written to the device; otherwise returns false.

This is a convenience function which checks if the OpenMode of the device contains the WriteOnly flag.

See also openMode() and OpenMode.

Opens the device and sets its OpenMode to mode. Returns true if successful; otherwise returns false. This function should be called from any reimplementations of open() or other functions that open the device.

See also openMode() and OpenMode.

Returns the mode in which the device has been opened; i.e. ReadOnly or WriteOnly.

See also setOpenMode() and OpenMode.

Reads at most maxSize bytes from the device into data, without side effects (i.e., if you call read() after peek(), you will get the same data). Returns the number of bytes read. If an error occurs, such as when attempting to peek a device opened in WriteOnly mode, this function returns -1.

0 is returned when no more data is available for reading.

Example:

See also read().

This is an overloaded function.

Peeks at most maxSize bytes from the device, returning the data peeked as a QByteArray.

Example:

This function has no way of reporting errors; returning an empty QByteArray() can mean either that no data was currently available for peeking, or that an error occurred.

See also read().

For random-access devices, this function returns the position that data is written to or read from. For sequential devices or closed devices, where there is no concept of a "current position", 0 is returned.

The current read/write position of the device is maintained internally by QIODevice, so reimplementing this function is not necessary. When subclassing QIODevice, use QIODevice::seek() to notify QIODevice about changes in the device position.

See also isSequential() and seek().

Writes the character c to the device. Returns true on success; otherwise returns false.

See also write(), getChar(), and ungetChar().

Reads at most maxSize bytes from the device into data, and returns the number of bytes read. If an error occurs, such as when attempting to read from a device opened in WriteOnly mode, this function returns -1.

0 is returned when no more data is available for reading. However, reading past the end of the stream is considered an error, so this function returns -1 in those cases (that is, reading on a closed socket or after a process has died).

See also readData(), readLine(), and write().

This is an overloaded function.

Reads at most maxSize bytes from the device, and returns the data read as a QByteArray.

This function has no way of reporting errors; returning an empty QByteArray() can mean either that no data was currently available for reading, or that an error occurred.

This is an overloaded function.

Reads all available data from the device, and returns it as a QByteArray.

This function has no way of reporting errors; returning an empty QByteArray() can mean either that no data was currently available for reading, or that an error occurred.

Reads up to maxSize bytes from the device into data, and returns the number of bytes read or -1 if an error occurred.

If there are no bytes to be read and there can never be more bytes available (examples include socket closed, pipe closed, sub-process finished), this function returns -1.

This function is called by QIODevice. Reimplement this function when creating a subclass of QIODevice.

See also read(), readLine(), and writeData().

This function reads a line of ASCII characters from the device, up to a maximum of maxSize - 1 bytes, stores the characters in data, and returns the number of bytes read. If a line could not be read but no error ocurred, this function returns 0. If an error occurs, this function returns the length of what could be read, or -1 if nothing was read.

A terminating '\0' byte is always appended to data, so maxSize must be larger than 1.

Data is read until either of the following conditions are met:

• The first '\n' character is read.
• maxSize - 1 bytes are read.
• The end of the device data is detected.

For example, the following code reads a line of characters from a file:

The newline character ('\n') is included in the buffer. If a newline is not encountered before maxSize - 1 bytes are read, a newline will not be inserted into the buffer. On windows newline characters are replaced with '\n'.

This function calls readLineData(), which is implemented using repeated calls to getChar(). You can provide a more efficient implementation by reimplementing readLineData() in your own subclass.

See also getChar(), read(), and write().

This is an overloaded function.

Reads a line from the device, but no more than maxSize characters, and returns the result as a QByteArray.

This function has no way of reporting errors; returning an empty QByteArray() can mean either that no data was currently available for reading, or that an error occurred.

Reads up to maxSize characters into data and returns the number of characters read.

This function is called by readLine(), and provides its base implementation, using getChar(). Buffered devices can improve the performance of readLine() by reimplementing this function.

readLine() appends a '\0' byte to data; readLineData() does not need to do this.

If you reimplement this function, be careful to return the correct value: it should return the number of bytes read in this line, including the terminating newline, or 0 if there is no line to be read at this point. If an error occurs, it should return -1 if and only if no bytes were read. Reading past EOF is considered an error.

Seeks to the start of input for random-access devices. Returns true on success; otherwise returns false (for example, if the device is not open).

Note that when using a QTextStream on a QFile, calling reset() on the QFile will not have the expected result because QTextStream buffers the file. Use the QTextStream::seek() function instead.

See also seek().

For random-access devices, this function sets the current position to pos, returning true on success, or false if an error occurred. For sequential devices, the default behavior is to do nothing and return false.

When subclassing QIODevice, you must call QIODevice::seek() at the start of your function to ensure integrity with QIODevice's built-in buffer. The base implementation always returns true.

See also pos() and isSequential().

Sets the human readable description of the last device error that occurred to str.

See also errorString().

Sets the OpenMode of the device to openMode. Call this function to set the open mode if the flags change after the device has been opened.

See also openMode() and OpenMode.

If enabled is true, this function sets the Text flag on the device; otherwise the Text flag is removed. This feature is useful for classes that provide custom end-of-line handling on a QIODevice.

See also isTextModeEnabled(), open(), and setOpenMode().

For open random-access devices, this function returns the size of the device. For open sequential devices, bytesAvailable() is returned.

If the device is closed, the size returned will not reflect the actual size of the device.

See also isSequential() and pos().

Puts the character c back into the device, and decrements the current position unless the position is 0. This function is usually called to "undo" a getChar() operation, such as when writing a backtracking parser.

If c was not previously read from the device, the behavior is undefined.

For buffered devices, this function waits until a payload of buffered written data has been written to the device and the bytesWritten() signal has been emitted, or until msecs milliseconds have passed. If msecs is -1, this function will not time out. For unbuffered devices, it returns immediately.

Returns true if a payload of data was written to the device; otherwise returns false (i.e. if the operation timed out, or if an error occurred).

This function can operate without an event loop. It is useful when writing non-GUI applications and when performing I/O operations in a non-GUI thread.

If called from within a slot connected to the bytesWritten() signal, bytesWritten() will not be reemitted.

Reimplement this function to provide a blocking API for a custom device. The default implementation does nothing, and returns false.

Warning: Calling this function from the main (GUI) thread might cause your user interface to freeze.

See also waitForReadyRead().

Blocks until new data is available for reading and the readyRead() signal has been emitted, or until msecs milliseconds have passed. If msecs is -1, this function will not time out.

Returns true if new data is available for reading; otherwise returns false (if the operation timed out or if an error occurred).

This function can operate without an event loop. It is useful when writing non-GUI applications and when performing I/O operations in a non-GUI thread.

If called from within a slot connected to the readyRead() signal, readyRead() will not be reemitted.

Reimplement this function to provide a blocking API for a custom device. The default implementation does nothing, and returns false.

Warning: Calling this function from the main (GUI) thread might cause your user interface to freeze.

See also waitForBytesWritten().

Writes at most maxSize bytes of data from data to the device. Returns the number of bytes that were actually written, or -1 if an error occurred.

See also read() and writeData().

This is an overloaded function.

Writes data from a zero-terminated string of 8-bit characters to the device. Returns the number of bytes that were actually written, or -1 if an error occurred. This is equivalent to

See also read() and writeData().

This is an overloaded function.

Writes the content of byteArray to the device. Returns the number of bytes that were actually written, or -1 if an error occurred.

See also read() and writeData().

Writes up to maxSize bytes from data to the device. Returns the number of bytes written, or -1 if an error occurred.

This function is called by QIODevice. Reimplement this function when creating a subclass of QIODevice.

See also read() and write().

Use pos() instead.

Use seek(offset) instead.

Use openMode() instead.

Use getChar() instead.

This functionality is no longer available. This function always returns true.

Use !(openMode() & QIODevice::Unbuffered) instead.

Use openMode() instead.

Use !isSequential() instead.

Use isOpen(), isReadable(), or isWritable() instead.

Use openMode() instead.

Use isSequential() instead.

This functionality is no longer available. This function always returns false.

Use openMode() instead.

Use openMode() instead.

Use putChar(ch) instead.

Use read(data, size) instead.

For device specific error handling, please refer to the individual device documentation.

See also qobject_cast().

Use isOpen() instead.

For device specific error handling, please refer to the individual device documentation.

See also qobject_cast().

Use ungetChar(ch) instead.

Use write(data, size) instead.

Use write(data) instead.