Qt Jambi Home

com.trolltech.qt.core
Class QFile

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
                  extended by com.trolltech.qt.core.QFile
All Implemented Interfaces:
QtJambiInterface
Direct Known Subclasses:
QTemporaryFile

public class QFile
extends QIODevice

The QFile class provides an interface for reading from and writing to files.

QFile is an I/O device for reading and writing text and binary files and resources. A QFile may be used by itself or, more conveniently, with a QTextStream or QDataStream.

The file name is usually passed in the constructor, but it can be set at any time using setFileName. QFile expects the file separator to be '/' regardless of operating system. The use of other separators (e.g., '\') is not supported.

You can check for a file's existence using exists, and remove a file using remove. (More advanced file system related operations are provided by QFileInfo and QDir.)

The file is opened with open, closed with close, and flushed with flush. Data is usually read and written using QDataStream or QTextStream, but you can also call the QIODevice-inherited functions read, readLine, readAll, write. QFile also inherits getChar(), putChar(), and ungetChar(), which work one character at a time.

The size of the file is returned by size. You can get the current file position using pos, or move to a new file position using seek. If you've reached the end of the file, atEnd returns true.

Reading Files Directly

The following example reads a text file line by line:

        QFile file("in.txt");
        if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
            return;

        while (!file.atEnd()) {
            QByteArray line = file.readLine();
            process_line(line);
        }

The QIODevice::Text flag passed to open tells Qt to convert Windows-style line terminators ("\r\n") into C++-style terminators ("\n"). By default, QFile assumes binary, i.e. it doesn't perform any conversion on the bytes stored in the file.

Using Streams to Read Files

The next example uses QTextStream to read a text file line by line:

        QFile file("in.txt");
        if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
            return;

        QTextStream in(&file);
        while (!in.atEnd()) {
            QString line = in.readLine();
            process_line(line);
        }

QTextStream takes care of converting the 8-bit data stored on disk into a 16-bit Unicode QString. By default, it assumes that the user system's local 8-bit encoding is used (e.g., ISO 8859-1 for most of Europe; see QTextCodec::codecForLocale() for details). This can be changed using setCodec().

To write text, we can use operator<<(), which is overloaded to take a QTextStream on the left and various data types (including QString) on the right:

        QFile file("out.txt");
        if (!file.open(QIODevice::WriteOnly | QIODevice::Text))
            return;

        QTextStream out(&file);
        out << "The magic number is: " << 49 << "\n";

QDataStream is similar, in that you can use operator<<() to write data and operator>>() to read it back. See the class documentation for details.

When you use QFile, QFileInfo, and QDir to access the file system with Qt, you can use Unicode file names. On Unix, these file names are converted to an 8-bit encoding. If you want to use standard C++ APIs (<cstdio> or <iostream>) or platform-specific APIs to access files instead of QFile, you can use the encodeName and decodeName functions to convert between Unicode file names and 8-bit file names.

On Unix, there are some special system files (e.g. in /proc) for which size will always return 0, yet you may still be able to read more data from such a file; the data is generated in direct response to you calling read. In this case, however, you cannot use atEnd to determine if there is more data to read (since atEnd will return true for a file that claims to have size 0). Instead, you should either call readAll, or call read or readLine repeatedly until no more data can be read. The next example uses QTextStream to read /proc/modules line by line:

        QFile file("/proc/modules");
        if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
            return;

        QTextStream in(&file);
        QString line = in.readLine();
        while (!line.isNull()) {
            process_line(line);
            line = in.readLine();
        }

Signals

Unlike other QIODevice implementations, such as QTcpSocket, QFile does not emit the aboutToClose, bytesWritten, or readyRead signals. This implementation detail means that QFile is not suitable for reading and writing certain types of files, such as device files on Unix platforms.

See Also:
QTextStream, QDataStream, QFileInfo, QDir, The Qt Resource System

Nested Class Summary
static class QFile.FileError
          This enum describes the errors that may be returned by the error function.
static class QFile.Permission
          This enum is used by the permission() function to report the permissions and ownership of a file.
static class QFile.Permissions
          This QFlag class provides flags for the int enum.
 
Nested classes/interfaces inherited from class com.trolltech.qt.core.QIODevice
QIODevice.OpenMode, QIODevice.OpenModeFlag
 
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
 
Fields inherited from class com.trolltech.qt.core.QIODevice
aboutToClose, bytesWritten, readyRead
 
Constructor Summary
QFile()
          
QFile(QObject parent)
          Constructs a new file object with the given parent.
QFile(java.lang.String name)
          Constructs a new file object to represent the file with the given name.
QFile(java.lang.String name, QObject parent)
          Constructs a new file object with the given parent to represent the file with the specified name.
 
Method Summary
 boolean atEnd()
          Returns true if the end of the file has been reached; otherwise returns false.
 void close()
          This function is reimplemented for internal reasons.
 boolean copy(java.lang.String newName)
          Copies the file currently specified by fileName to a file called newName.
static boolean copy(java.lang.String fileName, java.lang.String newName)
          Copies the file fileName to newName.
static java.lang.String decodeName(QByteArray localFileName)
          This does the reverse of QFile::encodeName() using localFileName.
static java.lang.String decodeName(java.lang.String localFileName)
          Returns the Unicode version of the given localFileName.
static QByteArray encodeName(java.lang.String fileName)
          By default, this function converts fileName to the local 8-bit encoding determined by the user's locale.
 QFile.FileError error()
          Returns the file error status.
 boolean exists()
          Returns true if the file specified by fileName exists; otherwise returns false.
static boolean exists(java.lang.String fileName)
          Returns true if the file specified by fileName exists; otherwise returns false.
 QAbstractFileEngine fileEngine()
          
 java.lang.String fileName()
          Returns the name set by setFileName or to the QFile constructors.
 boolean flush()
          Flushes any buffered data to the file.
static QFile fromNativePointer(QNativePointer nativePointer)
          This function returns the QFile instance pointed to by nativePointer
 int handle()
          Returns the file handle of the file.
 boolean isSequential()
          Returns true if the file can only be manipulated sequentially; otherwise returns false.
 boolean link(java.lang.String newName)
          Creates a link named newName that points to the file currently specified by fileName.
static boolean link(java.lang.String oldname, java.lang.String newName)
          Creates a link named newName that points to the file oldname.
 boolean open(int fd, QIODevice.OpenMode flags)
          Opens the existing file descripter fd in the given flags.
 boolean open(int fd, QIODevice.OpenModeFlag... flags)
          Opens the existing file descripter fd in the given flags.
 boolean open(QIODevice.OpenMode flags)
          Opens the file using OpenMode flags, returning true if successful; otherwise false.
 QFile.Permissions permissions()
          Returns the complete OR-ed together combination of QFile::Permission for the file.
static QFile.Permissions permissions(java.lang.String filename)
          Returns the complete OR-ed together combination of QFile::Permission for filename.
 long pos()
          This function is reimplemented for internal reasons.
protected  int readData(byte[] data)
          Equivalent to readData(data, ).
protected  int readLineData(byte[] data)
          Equivalent to readLineData(data, ).
 boolean remove()
          Removes the file specified by fileName.
static boolean remove(java.lang.String fileName)
          Removes the file specified by the fileName given.
 boolean rename(java.lang.String newName)
          Renames the file currently specified by fileName to newName.
static boolean rename(java.lang.String oldName, java.lang.String newName)
          Renames the file oldName to newName.
 boolean resize(long sz)
          Sets the file size (in bytes) sz.
static boolean resize(java.lang.String filename, long sz)
          Sets filename to size (in bytes) sz.
 boolean seek(long offset)
          For random-access devices, this function sets the current position to offset, returning true on success, or false if an error occurred.
 void setFileName(java.lang.String name)
          Sets the name of the file.
 boolean setPermissions(QFile.Permission... permissionSpec)
          Sets the permissions for the file to the permissionSpec specified.
 boolean setPermissions(QFile.Permissions permissionSpec)
          Sets the permissions for the file to the permissionSpec specified.
static boolean setPermissions(java.lang.String filename, QFile.Permission... permissionSpec)
          Sets the permissions for filename file to permissionSpec.
static boolean setPermissions(java.lang.String filename, QFile.Permissions permissionSpec)
          Sets the permissions for filename file to permissionSpec.
 long size()
          Returns the size of the file.
 java.lang.String symLinkTarget()
          Returns the absolute path of the file or directory a symlink (or shortcut on Windows) points to, or a an empty string if the object isn't a symbolic link.
static java.lang.String symLinkTarget(java.lang.String fileName)
          Returns the absolute path of the file or directory referred to by the symlink (or shortcut on Windows) specified by fileName, or returns an empty string if the fileName does not correspond to a symbolic link.
 void unsetError()
          Sets the file's error to QFile::NoError.
protected  int writeData(byte[] data)
          Equivalent to writeData(data, ).
 
Methods inherited from class com.trolltech.qt.core.QIODevice
bytesAvailable, bytesToWrite, canReadLine, errorString, getByte, isOpen, isReadable, isTextModeEnabled, isWritable, open, openMode, peek, peek, putByte, read, read, readAll, readLine, readLine, readLine, reset, setErrorString, setOpenMode, setOpenMode, setTextModeEnabled, ungetByte, waitForBytesWritten, waitForReadyRead, write, write
 
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
 

Constructor Detail

QFile

public QFile(java.lang.String name,
             QObject parent)

Constructs a new file object with the given parent to represent the file with the specified name.


QFile

public QFile(java.lang.String name)

Constructs a new file object to represent the file with the given name.


QFile

public QFile()


QFile

public QFile(QObject parent)

Constructs a new file object with the given parent.

Method Detail

copy

public final boolean copy(java.lang.String newName)

Copies the file currently specified by fileName to a file called newName. Returns true if successful; otherwise returns false.

Note that if a file with the name newName already exists, copy returns false (i.e. QFile will not overwrite it).

The source file is closed before it is copied.

See Also:
setFileName

error

public final QFile.FileError error()

Returns the file error status.

The I/O device status returns an error code. For example, if open returns false, or a read/write operation returns -1, this function can be called to find out the reason why the operation failed.

See Also:
unsetError

exists

public final boolean exists()

Returns true if the file specified by fileName exists; otherwise returns false.

See Also:
fileName, setFileName

fileName

public final java.lang.String fileName()

Returns the name set by setFileName or to the QFile constructors.

See Also:
setFileName, QFileInfo::fileName

flush

public final boolean flush()

Flushes any buffered data to the file. Returns true if successful; otherwise returns false.


handle

public final int handle()

Returns the file handle of the file.

This is a small positive integer, suitable for use with C library functions such as fdopen() and fcntl(). On systems that use file descriptors for sockets (i.e. Unix systems, but not Windows) the handle can be used with QSocketNotifier as well.

If the file is not open, or there is an error, handle returns -1.

See Also:
QSocketNotifier

link

public final boolean link(java.lang.String newName)

Creates a link named newName that points to the file currently specified by fileName. What a link is depends on the underlying filesystem (be it a shortcut on Windows or a symbolic link on Unix). Returns true if successful; otherwise returns false.

This function will not overwrite an already existing entity in the file system; in this case, link() will return false and set error() to return RenameError.

Note: To create a valid link on Windows, newName must have a .lnk file extension.

See Also:
setFileName

open

public final boolean open(int fd,
                          QIODevice.OpenModeFlag... flags)

Opens the existing file descripter fd in the given flags. Returns true if successful; otherwise returns false.

When a QFile is opened using this function, close does not actually close the file.

The QFile that is opened using this function is automatically set to be in raw mode; this means that the file input/output functions are slow. If you run into performance issues, you should try to use one of the other open functions.

Warning: If fd is 0 (stdin), 1 (stdout), or 2 (stderr), you may not be able to seek. size is set to LLONG_MAX (in <climits>).

See Also:
close

open

public final boolean open(int fd,
                          QIODevice.OpenMode flags)

Opens the existing file descripter fd in the given flags. Returns true if successful; otherwise returns false.

When a QFile is opened using this function, close does not actually close the file.

The QFile that is opened using this function is automatically set to be in raw mode; this means that the file input/output functions are slow. If you run into performance issues, you should try to use one of the other open functions.

Warning: If fd is 0 (stdin), 1 (stdout), or 2 (stderr), you may not be able to seek. size is set to LLONG_MAX (in <climits>).

See Also:
close

permissions

public final QFile.Permissions permissions()

Returns the complete OR-ed together combination of QFile::Permission for the file.

See Also:
setPermissions, setFileName

remove

public final boolean remove()

Removes the file specified by fileName. Returns true if successful; otherwise returns false.

The file is closed before it is removed.

See Also:
setFileName

rename

public final boolean rename(java.lang.String newName)

Renames the file currently specified by fileName to newName. Returns true if successful; otherwise returns false.

If a file with the name newName already exists, rename returns false (i.e., QFile will not overwrite it).

The file is closed before it is renamed.

See Also:
setFileName

resize

public final boolean resize(long sz)

Sets the file size (in bytes) sz. Returns true if the file if the resize succeeds; false otherwise. If sz is larger than the file currently is the new bytes will be set to 0, if sz is smaller the file is simply truncated.

See Also:
size, setFileName

setFileName

public final void setFileName(java.lang.String name)

Sets the name of the file. The name can have no path, a relative path, or an absolute path.

Do not call this function if the file has already been opened.

If the file name has no path or a relative path, the path used will be the application's current directory path at the time of the open call.

Example:

    QFile file;
    QDir::setCurrent("/tmp");
    file.setFileName("readme.txt");
    QDir::setCurrent("/home");
    file.open(QIODevice::ReadOnly);      // opens "/home/readme.txt" under Unix

Note that the directory separator "/" works for all operating systems supported by Qt.

See Also:
fileName, QFileInfo, QDir

setPermissions

public final boolean setPermissions(QFile.Permission... permissionSpec)

Sets the permissions for the file to the permissionSpec specified. Returns true if successful, or false if the permissions cannot be modified.

See Also:
permissions, setFileName

setPermissions

public final boolean setPermissions(QFile.Permissions permissionSpec)

Sets the permissions for the file to the permissionSpec specified. Returns true if successful, or false if the permissions cannot be modified.

See Also:
permissions, setFileName

symLinkTarget

public final java.lang.String symLinkTarget()

Returns the absolute path of the file or directory a symlink (or shortcut on Windows) points to, or a an empty string if the object isn't a symbolic link.

This name may not represent an existing file; it is only a string. QFile::exists() returns true if the symlink points to an existing file.

See Also:
fileName, setFileName

unsetError

public final void unsetError()

Sets the file's error to QFile::NoError.

See Also:
error

atEnd

public boolean atEnd()

Returns true if the end of the file has been reached; otherwise returns false.

For regular empty files on Unix (e.g. those in /proc), this function returns true, since the file system reports that the size of such a file is 0. Therefore, you should not depend on atEnd when reading data from such a file, but rather call read until no more data can be read.

Overrides:
atEnd in class QIODevice
See Also:
bytesAvailable, read, isSequential

close

public void close()

This function is reimplemented for internal reasons.

Overrides:
close in class QIODevice
See Also:
setOpenMode, OpenMode

fileEngine

public QAbstractFileEngine fileEngine()


isSequential

public boolean isSequential()

Returns true if the file can only be manipulated sequentially; otherwise returns false.

Most files support random-access, but some special files may not.

Overrides:
isSequential in class QIODevice
See Also:
QIODevice::isSequential

open

public boolean open(QIODevice.OpenMode flags)

Opens the file using OpenMode flags, returning true if successful; otherwise false.

The flags must be QIODevice::ReadOnly, QIODevice::WriteOnly, or QIODevice::ReadWrite. It may also have additional flags, such as QIODevice::Text and QIODevice::Unbuffered.

Note: In WriteOnly or ReadWrite mode, if the relevant file does not already exist, this function will try to create a new file before opening it.

Note: Because of limitations in the native API, QFile ignores the Unbuffered flag on Windows.

Overrides:
open in class QIODevice
See Also:
QIODevice::OpenMode, setFileName

pos

public long pos()

This function is reimplemented for internal reasons.

Overrides:
pos in class QIODevice
See Also:
isSequential, seek

readData

protected int readData(byte[] data)

Equivalent to readData(data, ).

Specified by:
readData in class QIODevice

readLineData

protected int readLineData(byte[] data)

Equivalent to readLineData(data, ).

Overrides:
readLineData in class QIODevice

seek

public boolean seek(long offset)

For random-access devices, this function sets the current position to offset, 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.

Overrides:
seek in class QIODevice
See Also:
pos, isSequential

size

public long size()

Returns the size of the file.

For regular empty files on Unix (e.g. those in /proc), this function returns 0; the contents of such a file are generated on demand in response to you calling read.

Overrides:
size in class QIODevice
See Also:
isSequential, pos

writeData

protected int writeData(byte[] data)

Equivalent to writeData(data, ).

Specified by:
writeData in class QIODevice

copy

public static boolean copy(java.lang.String fileName,
                           java.lang.String newName)

Copies the file fileName to newName. Returns true if successful; otherwise returns false.

If a file with the name newName already exists, copy returns false (i.e., QFile will not overwrite it).

See Also:
rename

decodeName

public static java.lang.String decodeName(QByteArray localFileName)

This does the reverse of QFile::encodeName() using localFileName.

See Also:
setDecodingFunction, encodeName

encodeName

public static QByteArray encodeName(java.lang.String fileName)

By default, this function converts fileName to the local 8-bit encoding determined by the user's locale. This is sufficient for file names that the user chooses. File names hard-coded into the application should only use 7-bit ASCII filename characters.

See Also:
decodeName, setEncodingFunction

exists

public static boolean exists(java.lang.String fileName)

Returns true if the file specified by fileName exists; otherwise returns false.


link

public static boolean link(java.lang.String oldname,
                           java.lang.String newName)

Creates a link named newName that points to the file oldname. What a link is depends on the underlying filesystem (be it a shortcut on Windows or a symbolic link on Unix). Returns true if successful; otherwise returns false.

See Also:
link

permissions

public static QFile.Permissions permissions(java.lang.String filename)

Returns the complete OR-ed together combination of QFile::Permission for filename.

See Also:
setPermissions

remove

public static boolean remove(java.lang.String fileName)

Removes the file specified by the fileName given.

Returns true if successful; otherwise returns false.

See Also:
remove

rename

public static boolean rename(java.lang.String oldName,
                             java.lang.String newName)

Renames the file oldName to newName. Returns true if successful; otherwise returns false.

If a file with the name newName already exists, rename returns false (i.e., QFile will not overwrite it).

See Also:
rename

resize

public static boolean resize(java.lang.String filename,
                             long sz)

Sets filename to size (in bytes) sz. Returns true if the file if the resize succeeds; false otherwise. If sz is larger than filename currently is the new bytes will be set to 0, if sz is smaller the file is simply truncated.

See Also:
resize

setPermissions

public static boolean setPermissions(java.lang.String filename,
                                     QFile.Permission... permissionSpec)

Sets the permissions for filename file to permissionSpec.

See Also:
permissions

setPermissions

public static boolean setPermissions(java.lang.String filename,
                                     QFile.Permissions permissionSpec)

Sets the permissions for filename file to permissionSpec.

See Also:
permissions

symLinkTarget

public static java.lang.String symLinkTarget(java.lang.String fileName)

Returns the absolute path of the file or directory referred to by the symlink (or shortcut on Windows) specified by fileName, or returns an empty string if the fileName does not correspond to a symbolic link.

This name may not represent an existing file; it is only a string. QFile::exists() returns true if the symlink points to an existing file.


fromNativePointer

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

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

decodeName

public static java.lang.String decodeName(java.lang.String localFileName)
Returns the Unicode version of the given localFileName. See encodeName() for details.


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