com.trolltech.qt.core
Class QFile

java.lang.Object
  extended by com.trolltech.qt.internal.QSignalEmitterInternal
      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 = new QFile("in.txt");
        if (!file.open(new QIODevice.OpenMode(QIODevice.OpenModeFlag.ReadOnly,
                                              QIODevice.OpenModeFlag.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 = new QFile("in.txt");
        if (!file.open(new QIODevice.OpenMode(QIODevice.OpenModeFlag.ReadOnly,
                                              QIODevice.OpenModeFlag.Text)))
            return;

        QTextStream in = new QTextStream(file);
        while (!in.atEnd()) {
            String 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 = new QFile("out.txt");
        if (!file.open(new QIODevice.OpenMode(QIODevice.OpenModeFlag.ReadOnly,
                                              QIODevice.OpenModeFlag.Text)))
            return;

        QTextStream out = new QTextStream(file);
        out.writeString("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 = new QFile("/proc/modules");
        if (!file.open(new QIODevice.OpenMode(QIODevice.OpenModeFlag.ReadOnly,
                                              QIODevice.OpenModeFlag.Text)))
            return;

        QTextStream in = new QTextStream(file);
        String line = in.readLine();
        while (line != null) {
            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.

Platform Specific Issues

File permissions are handled differently on Linux/Mac OS X and Windows. In a non
writable directory on Linux, files cannot be created. This is not always the case on Windows, where, for instance, the 'My Documents' directory usually is not writable, but it is still possible to create files in it.

See also:
QTextStream, QDataStream, QFileInfo, QDir, and 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.MemoryMapFlags
          This enum describes special options that may be used by the map() 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
           
 
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.PrivateSignal0, QSignalEmitter.PrivateSignal1, QSignalEmitter.PrivateSignal2, QSignalEmitter.PrivateSignal3, QSignalEmitter.PrivateSignal4, QSignalEmitter.PrivateSignal5, QSignalEmitter.PrivateSignal6, QSignalEmitter.PrivateSignal7, QSignalEmitter.PrivateSignal8, QSignalEmitter.PrivateSignal9, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9
 
Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal
 
Field Summary
 
Fields inherited from class com.trolltech.qt.core.QIODevice
aboutToClose, bytesWritten, readChannelFinished, readyRead
 
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
currentSender
 
Constructor Summary
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 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)
          This is an overloaded member function, provided for convenience.
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()
          This is an overloaded member function, provided for convenience.
static boolean exists(java.lang.String fileName)
          Returns true if the file specified by fileName exists; otherwise returns false.
 java.lang.String fileName()
          Returns the name set by setFileName() or to the QFile constructors.
 boolean flush()
          Flushes any buffered data to the file.
 int handle()
          Returns the file handle of the file.
 boolean link(java.lang.String newName)
          Creates a link named linkName that points to the file currently specified by fileName().
static boolean link(java.lang.String oldname, java.lang.String newName)
          This is an overloaded member function, provided for convenience.
 boolean open(int fd, QIODevice.OpenMode flags)
          This is an overloaded member function, provided for convenience.
 boolean open(int fd, QIODevice.OpenModeFlag[] flags)
          This is an overloaded method provided for convenience.
 boolean open(QIODevice.OpenMode flags)
          Opens the file using OpenModemode, 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)
          This is an overloaded member function, provided for convenience.
 boolean remove()
          Removes the file specified by fileName().
static boolean remove(java.lang.String fileName)
          This is an overloaded member function, provided for convenience.
 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)
          This is an overloaded member function, provided for convenience.
 boolean resize(long sz)
          Sets the file size (in bytes) sz.
static boolean resize(java.lang.String filename, long sz)
          This is an overloaded member function, provided for convenience.
 void setFileName(java.lang.String name)
          Sets the name of the file.
 boolean setPermissions(QFile.Permission[] permissionSpec)
          This is an overloaded method provided for convenience.
 boolean setPermissions(QFile.Permissions permissionSpec)
          Sets the permissions for the file to the permissions specified.
static boolean setPermissions(java.lang.String filename, QFile.Permission[] permissionSpec)
          This is an overloaded method provided for convenience.
static boolean setPermissions(java.lang.String filename, QFile.Permissions permissionSpec)
          This is an overloaded member function, provided for convenience.
 java.lang.String symLinkTarget()
          This is an overloaded member function, provided for convenience.
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 .
 
Methods inherited from class com.trolltech.qt.core.QIODevice
atEnd, bytesAvailable, bytesToWrite, canReadLine, close, errorString, getByte, isOpen, isReadable, isSequential, isTextModeEnabled, isWritable, open, openMode, peek, peek, pos, putByte, read, read, readAll, readData, readLine, readLine, readLine, readLineData, reset, seek, setErrorString, setOpenMode, setOpenMode, setTextModeEnabled, size, ungetByte, waitForBytesWritten, waitForReadyRead, write, write, writeData
 
Methods inherited from class com.trolltech.qt.core.QObject
childEvent, children, connectSlotsByName, customEvent, disposeLater, dumpObjectInfo, dumpObjectTree, dynamicPropertyNames, event, eventFilter, findChild, findChild, findChild, findChildren, findChildren, findChildren, findChildren, indexOfProperty, installEventFilter, isWidgetType, killTimer, moveToThread, objectName, parent, properties, property, removeEventFilter, setObjectName, setParent, setProperty, startTimer, timerEvent, toString, userProperty
 
Methods inherited from class com.trolltech.qt.QtJambiObject
dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr
 
Methods inherited from class com.trolltech.qt.QSignalEmitter
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread
 
Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
__qt_signalInitialization
 
Methods inherited from class java.lang.Object
clone, getClass, hashCode, notify, notifyAll, wait, wait, wait
 
Methods inherited from interface com.trolltech.qt.QtJambiInterface
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership
 

Constructor Detail

QFile

public QFile(QObject parent)
Constructs a new file object with the given parent.


QFile

public QFile(java.lang.String name)
Constructs a new file object to represent the file with the given name.


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.

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()
This is an overloaded member function, provided for convenience.

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

See also:
fileName(), and setFileName().


fileName

public final java.lang.String fileName()
Returns the name set by setFileName() or to the QFile constructors.

See also:
setFileName(), and 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.

This function is not supported on Windows CE.

See also:
QSocketNotifier.


link

public final boolean link(java.lang.String newName)
Creates a link named linkName 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, linkName must have a .lnk file extension.

See also:
setFileName().


open

public final boolean open(int fd,
                          QIODevice.OpenModeFlag[] flags)
This is an overloaded method provided for convenience.


open

public final boolean open(int fd,
                          QIODevice.OpenMode flags)
This is an overloaded member function, provided for convenience.

Opens the existing file descripter fd in the given mode. 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>).

Warning: For Windows CE you may not be able to call seek(), setSize(), fileTime(). size() is set to 0.

Warning: Since this function opens the file without specifying the file name, you cannot use this QFile with a QFileInfo.

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(), and 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(), and 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 = new QFile();
        QDir.setCurrent("/tmp");
        file.setFileName("readme.txt");
        QDir.setCurrent("/home");
        file.open(QIODevice.OpenModeFlag.ReadOnly);      // opens "/home/readme.txt" under Unix
Note that the directory separator "/" works for all operating systems supported by Qt.

See also:
fileName(), QFileInfo, and QDir.


setPermissions

public final boolean setPermissions(QFile.Permission[] permissionSpec)
This is an overloaded method provided for convenience.


setPermissions

public final boolean setPermissions(QFile.Permissions permissionSpec)
Sets the permissions for the file to the permissions specified. Returns true if successful, or false if the permissions cannot be modified.

See also:
permissions(), and setFileName().


symLinkTarget

public final java.lang.String symLinkTarget()
This is an overloaded member function, provided for convenience.

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(), and setFileName().


unsetError

public final void unsetError()
Sets the file's error to QFile::NoError .

See also:
error().


open

public boolean open(QIODevice.OpenMode flags)
Opens the file using OpenModemode, returning true if successful; otherwise false.

The mode 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.

See also:
QIODevice::OpenMode, and setFileName().

Overrides:
open in class QIODevice

copy

public static boolean copy(java.lang.String fileName,
                           java.lang.String newName)
This is an overloaded member function, provided for convenience.

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(), and 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(), and 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)
This is an overloaded member function, provided for convenience.

Creates a link named linkName that points to the file 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.

See also:
link().


permissions

public static QFile.Permissions permissions(java.lang.String filename)
This is an overloaded member function, provided for convenience.

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


remove

public static boolean remove(java.lang.String fileName)
This is an overloaded member function, provided for convenience.

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)
This is an overloaded member function, provided for convenience.

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)
This is an overloaded member function, provided for convenience.

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)
This is an overloaded method provided for convenience.


setPermissions

public static boolean setPermissions(java.lang.String filename,
                                     QFile.Permissions permissionSpec)
This is an overloaded member function, provided for convenience.

Sets the permissions for fileName file to 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.


decodeName

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