Qt 4.3: QAbstractFileEngine Class Reference

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# QAbstractFileEngine Class Reference
[QtCore module]

The QAbstractFileEngine class provides an abstraction for accessing the filesystem. More...

     #include <QAbstractFileEngine>

Inherited by QFSFileEngine.

Note: All the functions in this class are reentrant.

This class was introduced in Qt 4.1.

- List of all members, including inherited members

### Public Types

- class ExtensionOption
- class ExtensionReturn
- enum Extension { AtEndExtension, FastReadLineExtension }
- enum FileFlag { ReadOwnerPerm, WriteOwnerPerm, ExeOwnerPerm, ReadUserPerm, ..., Refresh }
- flags FileFlags
- enum FileName { DefaultName, BaseName, PathName, AbsoluteName, ..., BundleName }
- enum FileOwner { OwnerUser, OwnerGroup }
- enum FileTime { CreationTime, ModificationTime, AccessTime }
- typedef Iterator

### Public Functions

- virtual ~QAbstractFileEngine ()
- bool atEnd () const
- virtual Iterator * beginEntryList ( QDir::Filters filters, const QStringList & filterNames )
- virtual bool caseSensitive () const
- virtual bool close ()
- virtual bool copy ( const QString & newName )
- virtual QStringList entryList ( QDir::Filters filters, const QStringList & filterNames ) const
- QFile::FileError error () const
- QString errorString () const
- virtual bool extension ( Extension extension, const ExtensionOption * option = 0, ExtensionReturn * output = 0 )
- virtual FileFlags fileFlags ( FileFlags type = FileInfoAll ) const
- virtual QString fileName ( FileName file = DefaultName ) const
- virtual QDateTime fileTime ( FileTime time ) const
- virtual bool flush ()
- virtual int handle () const
- virtual bool isRelativePath () const
- virtual bool isSequential () const
- virtual bool link ( const QString & newName )
- virtual bool mkdir ( const QString & dirName, bool createParentDirectories ) const
- virtual bool open ( QIODevice::OpenMode mode )
- virtual QString owner ( FileOwner owner ) const
- virtual uint ownerId ( FileOwner owner ) const
- virtual qint64 pos () const
- virtual qint64 read ( char * data, qint64 maxlen )
- virtual qint64 readLine ( char * data, qint64 maxlen )
- virtual bool remove ()
- virtual bool rename ( const QString & newName )
- virtual bool rmdir ( const QString & dirName, bool recurseParentDirectories ) const
- virtual bool seek ( qint64 offset )
- virtual void setFileName ( const QString & file )
- virtual bool setPermissions ( uint perms )
- virtual bool setSize ( qint64 size )
- virtual qint64 size () const
- virtual bool supportsExtension ( Extension extension ) const
- virtual qint64 write ( const char * data, qint64 len )

### Static Public Members

- QAbstractFileEngine * create ( const QString & fileName )

### Protected Functions

- QAbstractFileEngine ()
- void setError ( QFile::FileError error, const QString & errorString )

### Related Non-Members

- typedef Iterator

## Detailed Description

The QAbstractFileEngine class provides an abstraction for accessing the filesystem.

The QDir, QFile, and QFileInfo classes all make use of a QAbstractFileEngine internally. If you create your own QAbstractFileEngine subclass (and register it with Qt by creating a QAbstractFileEngineHandler subclass), your file engine will be used when the path is one that your file engine handles.

A QAbstractFileEngine refers to one file or one directory. If the referent is a file, the setFileName(), rename(), and remove() functions are applicable. If the referent is a directory the mkdir(), rmdir(), and entryList() functions are applicable. In all cases the caseSensitive(), isRelativePath(), fileFlags(), ownerId(), owner(), and fileTime() functions are applicable.

A QAbstractFileEngine subclass can be created to do synchronous network I/O based file system operations, local file system operations, or to operate as a resource system to access file based resources.

See also QAbstractFileEngineHandler.

## Member Type Documentation

### enum QAbstractFileEngine::Extension

This enum describes the types of extensions that the file engine can support. Before using these extensions, you must verify that the extension is supported (i.e., call supportsExtension()).

Constant | Value | Description
--- | --- | ---
`QAbstractFileEngine::AtEndExtension` | `0` | Whether the current file position is at the end of the file or not. This extension allows file engines that implement local buffering to report end-of-file status without having to check the size of the file. It is also useful for sequential files, where the size of the file cannot be used to determine whether or not you have reached the end. This extension returns true if the file is at the end; otherwise it returns false. The input and output arguments to extension() are ignored.
`QAbstractFileEngine::FastReadLineExtension` | `1` | Whether the file engine provides a fast implementation for readLine() or not. If readLine() remains unimplemented in the file engine, QAbstractFileEngine will provide an implementation based on calling read() repeatedly. If supportsExtension() returns false for this extension, however, QIODevice can provide a faster implementation by making use of its internal buffer. For engines that already provide a fast readLine() implementation, returning false for this extension can avoid unnnecessary double-buffering in QIODevice.

This enum was introduced in Qt 4.3.

### enum QAbstractFileEngine::FileFlag
flags QAbstractFileEngine::FileFlags

The permissions and types of a file, suitable for OR'ing together.

Constant | Value | Description
--- | --- | ---
`QAbstractFileEngine::ReadOwnerPerm` | `0x4000` | The owner of the file has permission to read it.
`QAbstractFileEngine::WriteOwnerPerm` | `0x2000` | The owner of the file has permission to write to it.
`QAbstractFileEngine::ExeOwnerPerm` | `0x1000` | The owner of the file has permission to execute it.
`QAbstractFileEngine::ReadUserPerm` | `0x0400` | The current user has permission to read the file.
`QAbstractFileEngine::WriteUserPerm` | `0x0200` | The current user has permission to write to the file.
`QAbstractFileEngine::ExeUserPerm` | `0x0100` | The current user has permission to execute the file.
`QAbstractFileEngine::ReadGroupPerm` | `0x0040` | Members of the current user's group have permission to read the file.
`QAbstractFileEngine::WriteGroupPerm` | `0x0020` | Members of the current user's group have permission to write to the file.
`QAbstractFileEngine::ExeGroupPerm` | `0x0010` | Members of the current user's group have permission to execute the file.
`QAbstractFileEngine::ReadOtherPerm` | `0x0004` | All users have permission to read the file.
`QAbstractFileEngine::WriteOtherPerm` | `0x0002` | All users have permission to write to the file.
`QAbstractFileEngine::ExeOtherPerm` | `0x0001` | All users have permission to execute the file.
`QAbstractFileEngine::LinkType` | `0x10000` | The file is a link to another file (or link) in the file system (i.e. not a file or directory).
`QAbstractFileEngine::FileType` | `0x20000` | The file is a regular file to the file system (i.e. not a link or directory)
`QAbstractFileEngine::BundleType` | `0x80000` | The file is a Mac OS X bundle implies DirectoryType
`QAbstractFileEngine::DirectoryType` | `0x40000` | The file is a directory in the file system (i.e. not a link or file).
`QAbstractFileEngine::HiddenFlag` | `0x0100000` | The file is hidden.
`QAbstractFileEngine::ExistsFlag` | `0x0400000` | The file actually exists in the file system.
`QAbstractFileEngine::RootFlag` | `0x0800000` | The file or the file pointed to is the root of the filesystem.
`QAbstractFileEngine::LocalDiskFlag` | `0x0200000` | The file resides on the local disk and can be passed to standard file functions.
`QAbstractFileEngine::Refresh` | `0x1000000` | Passing this flag will force the file engine to refresh all flags.

The FileFlags type is a typedef for QFlags<FileFlag>. It stores an OR combination of FileFlag values.

See also fileFlags() and setFileName().

### enum QAbstractFileEngine::FileName

These values are used to request a file name in a particular format.

Constant | Value | Description
--- | --- | ---
`QAbstractFileEngine::DefaultName` | `0` | The same filename that was passed to the QAbstractFileEngine.
`QAbstractFileEngine::BaseName` | `1` | The name of the file excluding the path.
`QAbstractFileEngine::PathName` | `2` | The path to the file excluding the base name.
`QAbstractFileEngine::AbsoluteName` | `3` | The absolute path to the file (including the base name).
`QAbstractFileEngine::AbsolutePathName` | `4` | The absolute path to the file (excluding the base name).
`QAbstractFileEngine::LinkName` | `5` | The full file name of the file that this file is a link to. (This will be empty if this file is not a link.)
`QAbstractFileEngine::CanonicalName` | `6` | Often very similar to LinkName. Will return the true path to the file.
`QAbstractFileEngine::CanonicalPathName` | `7` | Same as CanonicalName, excluding the base name.
`QAbstractFileEngine::BundleName` | `8` | Returns the name of the bundle implies BundleType is set.

See also fileName() and setFileName().

### enum QAbstractFileEngine::FileOwner

Constant | Value | Description
--- | --- | ---
`QAbstractFileEngine::OwnerUser` | `0` | The user who owns the file.
`QAbstractFileEngine::OwnerGroup` | `1` | The group who owns the file.

See also owner(), ownerId(), and setFileName().

### enum QAbstractFileEngine::FileTime

These are used by the fileTime() function.

Constant | Value | Description
--- | --- | ---
`QAbstractFileEngine::CreationTime` | `0` | When the file was created.
`QAbstractFileEngine::ModificationTime` | `1` | When the file was most recently modified.
`QAbstractFileEngine::AccessTime` | `2` | When the file was most recently accessed (e.g. read or written to).

See also setFileName().

### typedef QAbstractFileEngine::Iterator

Synonym for QAbstractFileEngineIterator.

This typedef was introduced in Qt 4.3.

## Member Function Documentation

### QAbstractFileEngine::QAbstractFileEngine () `[protected]`

Constructs a new QAbstractFileEngine that does not refer to any file or directory.

See also setFileName().

### QAbstractFileEngine::~QAbstractFileEngine () `[virtual]`

Destroys the QAbstractFileEngine.

### bool QAbstractFileEngine::atEnd () const

Returns true if the current position is at the end of the file; otherwise, returns false.

This function bases its behavior on calling extension() with AtEndExtension. If the engine does not support this extension, false is returned.

This function was introduced in Qt 4.3.

See also extension(), supportsExtension(), and QFile::atEnd().

### Iterator * QAbstractFileEngine::beginEntryList ( QDir::Filters filters, const QStringList & filterNames ) `[virtual]`

Returns an instance of a QAbstractFileEngineIterator using filters for entry filtering and filterNames for name filtering. This function is called by QDirIterator to initiate directory iteration.

QDirIterator takes ownership of the returned instance, and deletes it when it's done.

See also QDirIterator.

### bool QAbstractFileEngine::caseSensitive () const `[virtual]`

Should return true if the underlying file system is case-sensitive; otherwise return false.

This virtual function must be reimplemented by all subclasses.

### bool QAbstractFileEngine::close () `[virtual]`

Closes the file, returning true if successful; otherwise returns false.

The default implementation always returns false.

### bool QAbstractFileEngine::copy ( const QString & newName ) `[virtual]`

Copies the contents of this file to a file with the name newName. Returns true on success; otherwise, false is returned.

### QAbstractFileEngine * QAbstractFileEngine::create ( const QString & fileName ) `[static]`

Creates and returns a QAbstractFileEngine suitable for processing fileName.

You should not need to call this function; use QFile, QFileInfo or QDir directly instead.

If you reimplemnt this function, it should only return file engines that knows how to handle fileName; otherwise, it should return 0.

See also QAbstractFileEngineHandler.

### QStringList QAbstractFileEngine::entryList ( QDir::Filters filters, const QStringList & filterNames ) const `[virtual]`

Requests that a list of all the files matching the filters list based on the filterNames in the file engine's directory are returned.

Should return an empty list if the file engine refers to a file rather than a directory, or if the directory is unreadable or does not exist or if nothing matches the specifications.

This virtual function must be reimplemented by all subclasses.

See also setFileName().

### QFile::FileError QAbstractFileEngine::error () const

Returns the QFile::FileError that resulted from the last failed operation. If QFile::UnspecifiedError is returned, QFile will use its own idea of the error status.

See also setError(), QFile::FileError, and errorString().

### QString QAbstractFileEngine::errorString () const

Returns the human-readable message appropriate to the current error reported by error(). If no suitable string is available, an empty string is returned.

See also error().

### bool QAbstractFileEngine::extension ( Extension extension, const ExtensionOption * option = 0, ExtensionReturn * output = 0 ) `[virtual]`

This virtual function can be reimplemented in a QAbstractFileEngine subclass to provide support for extensions. The option argument is provided as input to the extension, and this function can store output results in output.

The behavior of this function is determined by extension; see the Extension documentation for details.

You can call supportsExtension() to check if an extension is supported by the file engine.

By default, no extensions are supported, and this function returns false.

This function was introduced in Qt 4.3.

See also supportsExtension() and Extension.

### FileFlags QAbstractFileEngine::fileFlags ( FileFlags type = FileInfoAll ) const `[virtual]`

This function should return the set of OR'd flags that are true for the file engine's file, and that are in the type's OR'd members.

In your reimplementation you can use the type argument as an optimization hint and only return the OR'd set of members that are true and that match those in type; in other words you can ignore any members not mentioned in type, thus avoiding some potentially expensive lookups or system calls.

This virtual function must be reimplemented by all subclasses.

See also setFileName().

### QString QAbstractFileEngine::fileName ( FileName file = DefaultName ) const `[virtual]`

Return the file engine's current file name in the format specified by file.

If you don't handle some `FileName` possibilities, return the file name set in setFileName() when an unhandled format is requested.

This virtual function must be reimplemented by all subclasses.

See also setFileName() and FileName.

### QDateTime QAbstractFileEngine::fileTime ( FileTime time ) const `[virtual]`

If time is `CreationTime`, return when the file was created. If time is `ModificationTime`, return when the file was most recently modified. If time is `AccessTime`, return when the file was most recently accessed (e.g. read or written). If the time cannot be determined return QDateTime() (an invalid date time).

This virtual function must be reimplemented by all subclasses.

See also setFileName(), QDateTime, QDateTime::isValid(), and FileTime.

### bool QAbstractFileEngine::flush () `[virtual]`

Flushes the open file, returning true if successful; otherwise returns false.

The default implementation always returns false.

### int QAbstractFileEngine::handle () const `[virtual]`

Returns the native file handle for this file engine. This handle must be used with care; its value and type are platform specific, and using it will most likely lead to non-portable code.

### bool QAbstractFileEngine::isRelativePath () const `[virtual]`

Return true if the file referred to by this file engine has a relative path; otherwise return false.

This virtual function must be reimplemented by all subclasses.

See also setFileName().

### bool QAbstractFileEngine::isSequential () const `[virtual]`

Returns true if the file is a sequential access device; returns false if the file is a direct access device.

Operations involving size() and seek(int) are not valid on sequential devices.

### bool QAbstractFileEngine::link ( const QString & newName ) `[virtual]`

Creates a link from the file currently specified by fileName() to newName. 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.

### bool QAbstractFileEngine::mkdir ( const QString & dirName, bool createParentDirectories ) const `[virtual]`

Requests that the directory dirName be created. If createParentDirectories is true, then any sub-directories in dirName that don't exist must be created. If createParentDirectories is false then any sub-directories in dirName must already exist for the function to succeed. If the operation succeeds return true; otherwise return false.

This virtual function must be reimplemented by all subclasses.

See also setFileName(), rmdir(), and isRelativePath().

### bool QAbstractFileEngine::open ( QIODevice::OpenMode mode ) `[virtual]`

Opens the file in the specified mode. Returns true if the file was successfully opened; otherwise returns false.

The mode is an OR combination of QIODevice::OpenMode and QIODevice::HandlingMode values.

### QString QAbstractFileEngine::owner ( FileOwner owner ) const `[virtual]`

If owner is `OwnerUser` return the name of the user who owns the file. If owner is `OwnerGroup` return the name of the group that own the file. If you can't determine the owner return QString().

This virtual function must be reimplemented by all subclasses.

See also ownerId(), setFileName(), and FileOwner.

### uint QAbstractFileEngine::ownerId ( FileOwner owner ) const `[virtual]`

If owner is `OwnerUser` return the ID of the user who owns the file. If owner is `OwnerGroup` return the ID of the group that own the file. If you can't determine the owner return -2.

This virtual function must be reimplemented by all subclasses.

See also owner(), setFileName(), and FileOwner.

### qint64 QAbstractFileEngine::pos () const `[virtual]`

Returns the current file position.

This is the position of the data read/write head of the file.

### qint64 QAbstractFileEngine::read ( char * data, qint64 maxlen ) `[virtual]`

Reads a number of characters from the file into data. At most maxlen characters will be read.

Returns -1 if a fatal error occurs, or 0 if there are no bytes to read.

### qint64 QAbstractFileEngine::readLine ( char * data, qint64 maxlen ) `[virtual]`

This function reads one line, terminated by a '\n' character, from the file info data. At most maxlen characters will be read. The end-of-line character is included.

### bool QAbstractFileEngine::remove () `[virtual]`

Requests that the file is deleted from the file system. If the operation succeeds return true; otherwise return false.

This virtual function must be reimplemented by all subclasses.

See also setFileName() and rmdir().

### bool QAbstractFileEngine::rename ( const QString & newName ) `[virtual]`

Requests that the file be renamed to newName in the file system. If the operation succeeds return true; otherwise return false.

This virtual function must be reimplemented by all subclasses.

See also setFileName().

### bool QAbstractFileEngine::rmdir ( const QString & dirName, bool recurseParentDirectories ) const `[virtual]`

Requests that the directory dirName is deleted from the file system. When recurseParentDirectories is true, then any empty parent-directories in dirName must also be deleted. If recurseParentDirectories is false, only the dirName leaf-node should be deleted. In most file systems a directory cannot be deleted using this function if it is non-empty. If the operation succeeds return true; otherwise return false.

This virtual function must be reimplemented by all subclasses.

See also setFileName(), remove(), mkdir(), and isRelativePath().

### bool QAbstractFileEngine::seek ( qint64 offset ) `[virtual]`

Sets the file position to the given offset. Returns true if the position was successfully set; otherwise returns false.

The offset is from the beginning of the file, unless the file is sequential.

See also isSequential().

### void QAbstractFileEngine::setError ( QFile::FileError error, const QString & errorString ) `[protected]`

Sets the error type to error, and the error string to errorString. Call this function to set the error values returned by the higher-level classes.

See also QFile::error(), QIODevice::errorString(), and QIODevice::setErrorString().

### void QAbstractFileEngine::setFileName ( const QString & file ) `[virtual]`

Sets the file engine's file name to file. This file name is the file that the rest of the virtual functions will operate on.

This virtual function must be reimplemented by all subclasses.

See also fileName() and rename().

### bool QAbstractFileEngine::setPermissions ( uint perms ) `[virtual]`

Requests that the file's permissions be set to perms. The argument perms will be set to the OR-ed together combination of QAbstractFileEngine::FileInfo, with only the QAbstractFileEngine::PermsMask being honored. If the operations succceeds return true; otherwise return false;

This virtual function must be reimplemented by all subclasses.

See also size().

### bool QAbstractFileEngine::setSize ( qint64 size ) `[virtual]`

Requests that the file be set to size size. If size is larger than the current file then it is filled with 0's, if smaller it is simply truncated. If the operations succceeds return true; otherwise return false;

This virtual function must be reimplemented by all subclasses.

See also size().

### qint64 QAbstractFileEngine::size () const `[virtual]`

Returns the size of the file.

See also setSize().

### bool QAbstractFileEngine::supportsExtension ( Extension extension ) const `[virtual]`

This virtual function returns true if the file engine supports extension; otherwise, false is returned. By default, no extensions are supported.

This function was introduced in Qt 4.3.

See also extension().

### qint64 QAbstractFileEngine::write ( const char * data, qint64 len ) `[virtual]`

Writes len bytes from data to the file. Returns the number of characters written on success; otherwise returns -1.

## Related Non-Members

### typedef QAbstractFileEngine::Iterator

Synonym for QAbstractFileEngineIterator.

This typedef was introduced in Qt 4.3.