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com.trolltech.qt.core
Class QIODevice

java.lang.Object
  extended by com.trolltech.qt.QSignalEmitter
      extended by com.trolltech.qt.QtJambiObject
          extended by com.trolltech.qt.core.QObject
              extended by com.trolltech.qt.core.QIODevice
All Implemented Interfaces:
QtJambiInterface
Direct Known Subclasses:
QAbstractSocket, QBuffer, QFile, QProcess

public abstract class QIODevice
extends QObject

The QIODevice class is the base interface class of all I/O devices in Qt.

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. QIODevice is abstract and can not be instantiated, but it is common to use the interface it defines to provide device-independent I/O features. For example, Qt's XML classes operate on a QIODevice pointer, allowing them to be used with various devices (such as files and buffers).

Before accessing the device, open must be called to set the correct OpenMode (such as ReadOnly or ReadWrite). You can then write to the device with write or putChar(), and read by calling either read, readLine, or readAll. Call close when you are done with the device.

QIODevice distinguishes between two types of devices: random-access devices and sequential devices.

You can use isSequential to determine the type of device.

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 call bytesAvailable to determine the number of bytes that currently available for reading. 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. QIODevice emits the bytesWritten signal every time a payload of data has been written to the device. Use bytesToWrite to determine the current amount of data waiting to be written.

Certain subclasses of QIODevice, such as QTcpSocket and QProcess, are asynchronous. 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. 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 allows QIODevice subclasses to be used without an event loop, or in a separate thread:

Calling these functions from the main, GUI thread, may cause your user interface to freeze. Example:

    QProcess gzip;
    gzip.start("gzip", QStringList() << "-c");
    if (!gzip.waitForStarted())
        return false;

    gzip.write("uncompressed data");

    QByteArray compressed;
    while (gzip.waitForReadyRead())
        compressed += gzip.readAll();

By subclassing QIODevice, you can provide the same interface to your own I/O devices. Subclasses of QIODevice are only required to implement the protected readData and writeData functions. QIODevice uses these functions to implement all its convenience functions, such as getChar(), readLine and write. QIODevice also handles access control for you, so you can safely assume that the device is opened in write mode if writeData is called.

Some subclasses, such as QFile and QTcpSocket, are implemented using a memory buffer for intermediate storing of data. This reduces the number of required device accessing calls, which are often very slow. Buffering makes functions like getChar() and putChar() fast, as they can operate on the memory buffer instead of directly on the device itself. Certain I/O operations, however, don't work well with a buffer. For example, if several users open the same device and read it character by character, they may end up reading the same data when they meant to read a separate chunk each. For this reason, QIODevice allows you to bypass any buffering by passing the Unbuffered flag to open. When subclassing QIODevice, remember to bypass any buffer you may use when the device is open in Unbuffered mode.

See Also:
QBuffer, QFile, QTcpSocket

Nested Class Summary
static class QIODevice.OpenMode
          This QFlag class provides flags for the int enum.
static class QIODevice.OpenModeFlag
          This enum is used with open to describe the mode in which a device is opened.
 
Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter
QSignalEmitter.AbstractSignal, QSignalEmitter.Signal0, QSignalEmitter.Signal1<A>, QSignalEmitter.Signal2<A,B>, QSignalEmitter.Signal3<A,B,C>, QSignalEmitter.Signal4<A,B,C,D>, QSignalEmitter.Signal5<A,B,C,D,E>, QSignalEmitter.Signal6<A,B,C,D,E,F>, QSignalEmitter.Signal7<A,B,C,D,E,F,G>, QSignalEmitter.Signal8<A,B,C,D,E,F,G,H>, QSignalEmitter.Signal9<A,B,C,D,E,F,G,H,I>
 
Field Summary
 QSignalEmitter.Signal0 aboutToClose
          This signal is emitted when the device is about to close.
 QSignalEmitter.Signal1<java.lang.Long> bytesWritten
          This signal is emitted every time a payload of data has been written to the device.
 QSignalEmitter.Signal0 readyRead
          This signal is emitted once every time new data is available for reading from the device.
 
Constructor Summary
QIODevice()
          Constructs a QIODevice object.
QIODevice(QObject parent)
          Constructs a QIODevice object with the given parent.
 
Method Summary
 boolean atEnd()
          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.
 long bytesAvailable()
          Returns the number of bytes that are available for reading.
 long bytesToWrite()
          For buffered devices, this function returns the number of bytes waiting to be written.
 boolean canReadLine()
          Returns true if a complete line of data can be read from the device; otherwise returns false.
 void close()
          First emits aboutToClose, then closes the device and sets its OpenMode to NotOpen.
 java.lang.String errorString()
          Returns a human-readable description of the last device error that occurred.
static QIODevice fromNativePointer(QNativePointer nativePointer)
          This function returns the QIODevice instance pointed to by nativePointer
 int getByte()
          Gets a byte from the device.
 boolean isOpen()
          Returns true if the device is open; otherwise returns false.
 boolean isReadable()
          Returns true if data can be read from the device; otherwise returns false.
 boolean isSequential()
          Returns true if this device is sequential; otherwise returns false.
 boolean isTextModeEnabled()
          Returns true if the Text flag is enabled; otherwise returns false.
 boolean isWritable()
          Returns true if data can be written to the device; otherwise returns false.
 boolean open(QIODevice.OpenMode mode)
          Opens the device and sets its OpenMode to mode.
 boolean open(QIODevice.OpenModeFlag... mode)
          Opens the device and sets its OpenMode to mode.
 QIODevice.OpenMode openMode()
          Returns the mode in which the device has been opened; i.e. ReadOnly or WriteOnly.
 int peek(byte[] data)
          Reads from the device into data, without side effects (i.e., if you call read() after peek(), you will get the same data).
 QByteArray peek(long maxlen)
          Peeks at most maxlen bytes from the device, returning the data peeked as a QByteArray.
 long pos()
          For random-access devices, this function returns the position that data is written to or read from.
 boolean putByte(byte c)
          Writes the character c to the device.
 int read(byte[] data)
          Reads from the device into data.
 QByteArray read(long maxlen)
          Reads at most maxlen bytes from the device, and returns the data read as a QByteArray.
 QByteArray readAll()
          Reads all available data from the device, and returns it as a QByteArray.
protected abstract  int readData(byte[] data)
          Equivalent to readData(data, ).
 QByteArray readLine()
          Equivalent to readLine(0).
 int readLine(byte[] data)
          This functions reads a line of ASCII characters from the device (the maximum characters read is the length of data).
 QByteArray readLine(long maxlen)
          Reads a line from the device, but no more than maxlen characters, and returns the result as a QByteArray.
protected  int readLineData(byte[] data)
          Equivalent to readLineData(data, ).
 boolean reset()
          Seeks to the start of input for random-access devices.
 boolean seek(long pos)
          For random-access devices, this function sets the current position to pos, returning true on success, or false if an error occurred.
protected  void setErrorString(java.lang.String errorString)
          Sets the human readable description of the last device error that occurred to errorString.
protected  void setOpenMode(QIODevice.OpenMode openMode)
          Sets the OpenMode of the device to openMode.
protected  void setOpenMode(QIODevice.OpenModeFlag... openMode)
          Sets the OpenMode of the device to openMode.
 void setTextModeEnabled(boolean enabled)
          If enabled is true, this function sets the Text flag on the device; otherwise the Text flag is removed.
 long size()
          For open random-access devices, this function returns the size of the device.
 void ungetByte(byte c)
          Puts the character c back into the device, and decrements the current position unless the position is 0.
 boolean waitForBytesWritten(int msecs)
          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.
 boolean waitForReadyRead(int msecs)
          Blocks until data is available for reading and the readyRead signal has been emitted, or until msecs milliseconds have passed.
 int write(byte[] data)
          Writes data to the device.
 long write(QByteArray data)
          Writes the content of data to the device.
protected abstract  int writeData(byte[] data)
          Equivalent to writeData(data, ).
 
Methods inherited from class com.trolltech.qt.core.QObject
blockSignals, childEvent, children, connectSlotsByName, customEvent, disposeLater, dumpObjectInfo, dumpObjectTree, dynamicPropertyNames, event, eventFilter, findChild, findChild, findChild, findChildren, findChildren, findChildren, findChildren, installEventFilter, isWidgetType, killTimer, moveToThread, objectName, parent, property, removeEventFilter, setObjectName, setParent, setProperty, signalsBlocked, startTimer, thread, timerEvent
 
Methods inherited from class com.trolltech.qt.QtJambiObject
dispose, disposed, finalize, reassignNativeResources, tr, tr, tr
 
Methods inherited from class com.trolltech.qt.QSignalEmitter
disconnect, disconnect, signalSender
 
Methods inherited from class java.lang.Object
clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface com.trolltech.qt.QtJambiInterface
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership
 

Field Detail

aboutToClose

public final QSignalEmitter.Signal0 aboutToClose

This signal is emitted when the device is about to close. Connect this signal if you have operations that need to be performed before the device closes (e.g., if you have data in a separate buffer that needs to be written to the device).

Compatible Slot Signature:
void mySlot()


bytesWritten

public final QSignalEmitter.Signal1<java.lang.Long> bytesWritten

This signal is emitted every time a payload of data has been written to the device. The bytes argument is set to the number of bytes that were written in this payload.

bytesWritten is not emitted recursively; if you reenter the event loop or call waitForBytesWritten inside a slot connected to the bytesWritten signal, the signal will not be reemitted (although waitForBytesWritten may still return true).

Compatible Slot Signatures:
void mySlot(long bytes)
void mySlot()
See Also:
readyRead


readyRead

public final QSignalEmitter.Signal0 readyRead

This signal is emitted once every time new data is available for reading from the device. It will only be emitted again once new data is available, such as when a new payload of network data has arrived on your network socket, or when a new block of data has been appended to your device.

readyRead is not emitted recursively; if you reenter the event loop or call waitForReadyRead inside a slot connected to the readyRead signal, the signal will not be reemitted (although waitForReadyRead may still return true).

Compatible Slot Signature:
void mySlot()
See Also:
bytesWritten

Constructor Detail

QIODevice

public QIODevice()

Constructs a QIODevice object.


QIODevice

public QIODevice(QObject parent)

Constructs a QIODevice object with the given parent.

Method Detail

errorString

public final java.lang.String errorString()

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

See Also:
setErrorString

isOpen

public final boolean isOpen()

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, OpenMode

isReadable

public final boolean isReadable()

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, OpenMode

isTextModeEnabled

public final boolean isTextModeEnabled()

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

See Also:
setTextModeEnabled

isWritable

public final boolean isWritable()

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, OpenMode

openMode

public final QIODevice.OpenMode openMode()

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

See Also:
setOpenMode, OpenMode

peek

public final QByteArray peek(long maxlen)

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

Example:

    bool isExeFile(QFile *file)
    {
        return file->peek(2) == "MZ";
    }

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

putByte

public final boolean putByte(byte c)

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

See Also:
write, getChar, ungetChar

read

public final QByteArray read(long maxlen)

Reads at most maxlen 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.


readAll

public final QByteArray readAll()

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.


readLine

public final QByteArray readLine()

Equivalent to readLine(0).


readLine

public final QByteArray readLine(long maxlen)

Reads a line from the device, but no more than maxlen 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.


setErrorString

protected final void setErrorString(java.lang.String errorString)

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

See Also:
errorString

setOpenMode

protected final void setOpenMode(QIODevice.OpenModeFlag... openMode)

Sets the OpenMode of the device to openMode. Call this function to set the open mode when reimplementing open.

See Also:
openMode, OpenMode

setOpenMode

protected final void setOpenMode(QIODevice.OpenMode openMode)

Sets the OpenMode of the device to openMode. Call this function to set the open mode when reimplementing open.

See Also:
openMode, OpenMode

setTextModeEnabled

public final void setTextModeEnabled(boolean enabled)

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, setOpenMode

ungetByte

public final void ungetByte(byte c)

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.


write

public final long write(QByteArray data)

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

See Also:
read, writeData

atEnd

public boolean atEnd()

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, isSequential

bytesAvailable

public long bytesAvailable()

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:

    qint64 CustomDevice::bytesAvailable() const
    {
        return buffer.size() + QIODevice::bytesAvailable();
    }

See Also:
bytesToWrite, readyRead, isSequential

bytesToWrite

public long bytesToWrite()

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, isSequential

canReadLine

public boolean canReadLine()

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 size of the QIODevice's buffer. Example:

    bool CustomDevice::canReadLine() const
    {
        return buffer.contains('\n') || QIODevice::canReadLine();
    }

See Also:
readyRead, readLine

close

public void close()

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

See Also:
setOpenMode, OpenMode

isSequential

public boolean isSequential()

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

open

public final boolean open(QIODevice.OpenModeFlag... mode)
Opens the device and sets its OpenMode to mode. Returns true if successful; otherwise returns false.


open

public boolean open(QIODevice.OpenMode mode)

Opens the device and sets its OpenMode to mode. Returns true if successful; otherwise returns false.

See Also:
openMode, OpenMode

pos

public long pos()

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, seek

readData

protected abstract int readData(byte[] data)

Equivalent to readData(data, ).


readLineData

protected int readLineData(byte[] data)

Equivalent to readLineData(data, ).


reset

public boolean reset()

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

seek

public boolean seek(long pos)

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, isSequential

size

public long size()

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, pos

waitForBytesWritten

public boolean waitForBytesWritten(int msecs)

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

waitForReadyRead

public boolean waitForReadyRead(int msecs)

Blocks until 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 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

writeData

protected abstract int writeData(byte[] data)

Equivalent to writeData(data, ).


fromNativePointer

public static QIODevice fromNativePointer(QNativePointer nativePointer)
This function returns the QIODevice instance pointed to by nativePointer

Parameters:
nativePointer - the QNativePointer of which object should be returned.

getByte

public final int getByte()
Gets a byte from the device.

Returns:
-1 on failure, or the value of the byte on success

peek

public final int peek(byte[] data)
Reads 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.


read

public final int read(byte[] data)
Reads from the device into 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.


readLine

public final int readLine(byte[] data)
This functions reads a line of ASCII characters from the device (the maximum characters read is the length of data). The data is placed in data. It returns -1 if an error occurs.


write

public final int write(byte[] data)
Writes data to the device. Returns the number of bytes that were actually written, or -1 if an error occurred.


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