waitFor.() - Subclasses of QIODevice implement blocking functions for device-specific operations.waitForBytesWritten() - This function suspends operation in the calling thread until one payload of data has been written to the device.

waitForReadyRead() - This function suspends operation in the calling thread until new data is available for reading.This allows QIODevice subclasses to be used without an event loop, or in a separate thread: QIODevice provides functions that allow you to force these operations to be performed immediately, while blocking the calling thread and without entering the event loop.

This means that I/O functions such as write() or read() always return immediately, while communication with the device itself may happen when control goes back to the event loop. Use bytesToWrite() to determine the current amount of data waiting to be written.Ĭertain subclasses of QIODevice, such as QTcpSocket and QProcess, are asynchronous. QIODevice emits the bytesWritten() signal every time a payload of data has been written to the device. It's common to use bytesAvailable() together with the readyRead() signal when programming with asynchronous devices such as QTcpSocket, where fragments of data can arrive at arbitrary points in time. You can call bytesAvailable() to determine the number of bytes that are currently available for reading. QIODevice emits readyRead() when new data is available for reading for example, if new data has arrived on the network or if additional data is appended to a file that you are reading from. You can use isSequential() to determine the type of device. QTcpSocket and QProcess are examples of sequential devices. The functions pos() and size() don't work for sequential devices.

Sequential devices don't support seeking to arbitrary positions.

QFile and QBuffer are examples of random-access devices. The current position in the file is available by calling pos().

Random-access devices support seeking to arbitrary positions using seek().

QIODevice distinguishes between two types of devices: random-access devices and sequential devices. Call close() when you are done with the device. You can then write to the device with write() or putChar(), and read by calling either read(), readLine(), or readAll(). For example, Qt's XML classes operate on a QIODevice pointer, allowing them to be used with various devices (such as files and buffers).īefore accessing the device, open() must be called to set the correct OpenMode (such as ReadOnly or ReadWrite). QIODevice is abstract and cannot be instantiated, but it is common to use the interface it defines to provide device-independent I/O features.

ReadToEndAsync - Reads all characters from the current position to the end of the stream asynchronously and returns them as one string.QIODevice provides both a common implementation and an abstract interface for devices that support reading and writing of blocks of data, such as QFile, QBuffer and QTcpSocket.

ReadToEnd - Reads all characters from the current position to the end of the stream.

ReadLineAsync - Reads a line of characters asynchronously from the current stream and returns the data as a string.

ReadLine - Reads a line of characters from the current stream and returns the data as a string.

ReadBlockAsync - Reads a specified maximum number of characters from the current stream asynchronously and writes the data to a buffer, beginning at the specified index.

ReadBlock - Reads a specified maximum number of characters from the current stream and writes the data to a buffer, beginning at the specified index.

ReadAsync - Reads a specified maximum number of characters from the current stream asynchronously and writes the data to a buffer, beginning at the specified index.

Read - Reads the next character or next set of characters from the input stream.

Peak – Returns if there is a character or not.

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