Contents

• Public Types
• Public Functions
• Static Public Members
• Protected Functions
• Related Non-Members
• Detailed Description

Detailed Description

TheQAbstractFileEngine class provides an abstraction for accessing the filesystem.

TheQDir,QFile, andQFileInfo classes all make use of aQAbstractFileEngine internally. If you create your ownQAbstractFileEngine subclass (and register it with Qt by creating aQAbstractFileEngineHandler subclass), your file engine will be used when the path is one that your file engine handles.

AQAbstractFileEngine refers to one file or one directory. If the referent is a file, thesetFileName(),rename(), andremove() functions are applicable. If the referent is a directory themkdir(),rmdir(), andentryList() functions are applicable. In all cases thecaseSensitive(),isRelativePath(),fileFlags(),ownerId(),owner(), andfileTime() functions are applicable.

AQAbstractFileEngine 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.

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., callsupportsExtension()).

This enum was introduced or modified in Qt 4.3.

enum QAbstractFileEngine::FileFlag
flags QAbstractFileEngine::FileFlags

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

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

See alsofileFlags() andsetFileName().

enum QAbstractFileEngine::FileName

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

See alsofileName() andsetFileName().

enum QAbstractFileEngine::FileOwner

See alsoowner(),ownerId(), andsetFileName().

enum QAbstractFileEngine::FileTime

These are used by thefileTime() function.

See alsosetFileName().

typedef QAbstractFileEngine::Iterator

Synonym forQAbstractFileEngineIterator.

This typedef was introduced in Qt 4.3.

Member Function Documentation

[protected]QAbstractFileEngine::QAbstractFileEngine()

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

See alsosetFileName().

[virtual]QAbstractFileEngine::~QAbstractFileEngine()

Destroys theQAbstractFileEngine.

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 callingextension() withAtEndExtension. If the engine does not support this extension, false is returned.

This function was introduced in Qt 4.3.

See alsoextension(),supportsExtension(), andQFile::atEnd().

[virtual]Iterator * QAbstractFileEngine::beginEntryList(QDir::Filters filters, constQStringList & filterNames)

Returns an instance of aQAbstractFileEngineIterator usingfilters for entry filtering andfilterNames for name filtering. This function is called byQDirIterator to initiate directory iteration.

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

See alsoQDirIterator.

[virtual]bool QAbstractFileEngine::caseSensitive() const

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

This virtual function must be reimplemented by all subclasses.

[virtual]bool QAbstractFileEngine::close()

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

The default implementation always returns false.

[virtual]bool QAbstractFileEngine::copy(constQString & newName)

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

[static]QAbstractFileEngine * QAbstractFileEngine::create(constQString & fileName)

Creates and returns aQAbstractFileEngine suitable for processingfileName.

You should not need to call this function; useQFile,QFileInfo orQDir directly instead.

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

See alsoQAbstractFileEngineHandler.

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

Requests that a list of all the files matching thefilters list based on thefilterNames 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 alsosetFileName().

QFile::FileError QAbstractFileEngine::error() const

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

See alsosetError(),QFile::FileError, anderrorString().

QString QAbstractFileEngine::errorString() const

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

See alsoerror().

[virtual]bool QAbstractFileEngine::extension(Extension extension, constExtensionOption * option = 0,ExtensionReturn * output = 0)

This virtual function can be reimplemented in aQAbstractFileEngine subclass to provide support for extensions. Theoption argument is provided as input to the extension, and this function can store output results inoutput.

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

You can callsupportsExtension() 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 alsosupportsExtension() andExtension.

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

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

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

This virtual function must be reimplemented by all subclasses.

See alsosetFileName().

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

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

If you don't handle someFileName possibilities, return the file name set insetFileName() when an unhandled format is requested.

This virtual function must be reimplemented by all subclasses.

See alsosetFileName() andFileName.

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

Iftime isCreationTime, return when the file was created. Iftime isModificationTime, return when the file was most recently modified. Iftime isAccessTime, 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 alsosetFileName(),QDateTime,QDateTime::isValid(), andFileTime.

[virtual]bool QAbstractFileEngine::flush()

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

The default implementation always returns false.

[virtual]int QAbstractFileEngine::handle() const

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.

[virtual]bool QAbstractFileEngine::isRelativePath() const

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 alsosetFileName().

[virtual]bool QAbstractFileEngine::isSequential() const

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

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

[virtual]bool QAbstractFileEngine::link(constQString & newName)

Creates a link from the file currently specified byfileName() tonewName. 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.

uchar * QAbstractFileEngine::map(qint64 offset,qint64 size,QFile::MemoryMapFlags flags)

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

This function bases its behavior on callingextension() withMapExtensionOption. 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 alsounmap() andsupportsExtension().

[virtual]bool QAbstractFileEngine::mkdir(constQString & dirName,bool createParentDirectories) const

Requests that the directorydirName be created. IfcreateParentDirectories is true, then any sub-directories indirName that don't exist must be created. IfcreateParentDirectories is false then any sub-directories indirName 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 alsosetFileName(),rmdir(), andisRelativePath().

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

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

Themode is an OR combination ofQIODevice::OpenMode and QIODevice::HandlingMode values.

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

Ifowner isOwnerUser return the name of the user who owns the file. Ifowner isOwnerGroup 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 alsoownerId(),setFileName(), andFileOwner.

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

Ifowner isOwnerUser return the ID of the user who owns the file. Ifowner isOwnerGroup 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 alsoowner(),setFileName(), andFileOwner.

[virtual]qint64 QAbstractFileEngine::pos() const

Returns the current file position.

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

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

Reads a number of characters from the file intodata. At mostmaxlen characters will be read.

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

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

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

[virtual]bool QAbstractFileEngine::remove()

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 alsosetFileName() andrmdir().

[virtual]bool QAbstractFileEngine::rename(constQString & newName)

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

This virtual function must be reimplemented by all subclasses.

See alsosetFileName().

[virtual]bool QAbstractFileEngine::rmdir(constQString & dirName,bool recurseParentDirectories) const

Requests that the directorydirName is deleted from the file system. WhenrecurseParentDirectories is true, then any empty parent-directories indirName must also be deleted. IfrecurseParentDirectories is false, only thedirName 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 alsosetFileName(),remove(),mkdir(), andisRelativePath().

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

Sets the file position to the givenoffset. 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 alsoisSequential().

[protected]void QAbstractFileEngine::setError(QFile::FileError error, constQString & errorString)

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

See alsoQFile::error(),QIODevice::errorString(), andQIODevice::setErrorString().

[virtual]void QAbstractFileEngine::setFileName(constQString & file)

Sets the file engine's file name tofile. 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 alsofileName() andrename().

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

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

This virtual function must be reimplemented by all subclasses.

See alsosize().

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

Requests that the file be set to sizesize. Ifsize 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 alsosize().

[virtual]qint64 QAbstractFileEngine::size() const

Returns the size of the file.

See alsosetSize().

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

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

This function was introduced in Qt 4.3.

See alsoextension().

bool QAbstractFileEngine::unmap(uchar * address)

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

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

This function was introduced in Qt 4.4.

See alsomap() andsupportsExtension().

[virtual]qint64 QAbstractFileEngine::write(constchar * data,qint64 len)

Writeslen bytes fromdata to the file. Returns the number of characters written on success; otherwise returns -1.

Related Non-Members

typedef QAbstractFileEngine::Iterator

Synonym forQAbstractFileEngineIterator.

This typedef was introduced in Qt 4.3.