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QAbstractFileEngine Class Reference
[QtCore module]

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

Inherited by QFSFileEngine.

Types

Methods

Static Methods


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.


Type Documentation

QAbstractFileEngine.FileFlag

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().

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().

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().

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().


Method Documentation

QAbstractFileEngine.__init__ (self)

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

See also setFileName().

bool QAbstractFileEngine.atEnd (self)

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().

QAbstractFileEngineIterator QAbstractFileEngine.beginEntryList (self, QDir.Filters filters, QStringList filterNames)

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 (self)

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 (self)

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

The default implementation always returns false.

bool QAbstractFileEngine.copy (self, QString newName)

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

QAbstractFileEngine QAbstractFileEngine.create (QString fileName)

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 (self, QDir.Filters filters, QStringList filterNames)

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 (self)

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 (self)

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().

FileFlags QAbstractFileEngine.fileFlags (self, FileFlags type = QAbstractFileEngine.FileInfoAll)

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 (self, FileName file = QAbstractFileEngine.DefaultName)

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 (self, FileTime time)

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 (self)

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

The default implementation always returns false.

int QAbstractFileEngine.handle (self)

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 (self)

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 (self)

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 (self, QString newName)

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.

sip.voidptr QAbstractFileEngine.map (self, int offset, int size, QFile.MemoryMapFlags flags)

Maps size bytes of the file into memory starting at offset. Returns a pointer to the memory if successful; otherwise returns false if, for example, an error occurs.

This function bases its behavior on calling extension() with MapExtensionOption. If the engine does not support this extension, 0 is returned.

flags is currently not used, but could be used in the future.

This function was introduced in Qt 4.4.

See also unmap() and supportsExtension().

bool QAbstractFileEngine.mkdir (self, QString dirName, bool createParentDirectories)

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 (self, QIODevice.OpenMode openMode)

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 (self, FileOwner)

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.

int QAbstractFileEngine.ownerId (self, FileOwner)

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.

int QAbstractFileEngine.pos (self)

Returns the current file position.

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

object QAbstractFileEngine.read (self, int maxlen)

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.

object QAbstractFileEngine.readLine (self, int maxlen)

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 (self)

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 (self, QString newName)

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 (self, QString dirName, bool recurseParentDirectories)

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 (self, int pos)

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().

QAbstractFileEngine.setError (self, QFile.FileError error, QString str)

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().

QAbstractFileEngine.setFileName (self, QString file)

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 (self, int perms)

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 (self, int size)

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().

int QAbstractFileEngine.size (self)

Returns the size of the file.

See also setSize().

bool QAbstractFileEngine.unmap (self, sip.voidptr ptr)

Unmaps the memory address. Returns true if the unmap succeeds; otherwise returns false.

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

This function was introduced in Qt 4.4.

See also map() and supportsExtension().

int QAbstractFileEngine.write (self, bytes data)

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


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