QFileDevice Class
The QFileDevice class provides an interface for reading from and writing to open files. More...
| Header: | #include <QFileDevice> |
| qmake: | QT += core |
| Since: | Qt 5.0 |
| Inherits: | QIODevice |
| Inherited By: |
This class was introduced in Qt 5.0.
Note: All functions in this class are reentrant.
Public Types
| enum | FileError { NoError, ReadError, WriteError, FatalError, ResourceError, …, CopyError } |
| enum | FileHandleFlag { AutoCloseHandle, DontCloseHandle } |
| enum | FileTime { FileAccessTime, FileBirthTime, FileMetadataChangeTime, FileModificationTime } |
| enum | MemoryMapFlags { NoOptions, MapPrivateOption } |
| enum | Permission { ReadOwner, WriteOwner, ExeOwner, ReadUser, WriteUser, …, ExeOther } |
Detailed Description
QFileDevice is the base class for I/O devices that can read and write text and binary files and resources. QFile offers the main functionality, QFileDevice serves as a base class for sharing functionality with other file devices such as QTemporaryFile, by providing all the operations that can be done on files that have been opened by QFile or QTemporaryFile.
See also QFile and QTemporaryFile.
Member Type Documentation
enum QFileDevice::FileError
This enum describes the errors that may be returned by the error() function.
| Constant | Value | Description |
|---|---|---|
QFileDevice::NoError | 0 | No error occurred. |
QFileDevice::ReadError | 1 | An error occurred when reading from the file. |
QFileDevice::WriteError | 2 | An error occurred when writing to the file. |
QFileDevice::FatalError | 3 | A fatal error occurred. |
QFileDevice::ResourceError | 4 | Out of resources (e.g., too many open files, out of memory, etc.) |
QFileDevice::OpenError | 5 | The file could not be opened. |
QFileDevice::AbortError | 6 | The operation was aborted. |
QFileDevice::TimeOutError | 7 | A timeout occurred. |
QFileDevice::UnspecifiedError | 8 | An unspecified error occurred. |
QFileDevice::RemoveError | 9 | The file could not be removed. |
QFileDevice::RenameError | 10 | The file could not be renamed. |
QFileDevice::PositionError | 11 | The position in the file could not be changed. |
QFileDevice::ResizeError | 12 | The file could not be resized. |
QFileDevice::PermissionsError | 13 | The file could not be accessed. |
QFileDevice::CopyError | 14 | The file could not be copied. |
enum QFileDevice::FileHandleFlag
This enum is used when opening a file to specify additional options which only apply to files and not to a generic QIODevice.
| Constant | Value | Description |
|---|---|---|
QFileDevice::AutoCloseHandle | 0x0001 | The file handle passed into open() should be closed by close(), the default behavior is that close just flushes the file and the application is responsible for closing the file handle. When opening a file by name, this flag is ignored as Qt always owns the file handle and must close it. |
QFileDevice::DontCloseHandle | 0 | If not explicitly closed, the underlying file handle is left open when the QFile object is destroyed. |
enum QFileDevice::FileTime
This enum is used by the fileTime() and setFileTime() functions.
| Constant | Value | Description |
|---|---|---|
QFileDevice::FileAccessTime | 0 | When the file was most recently accessed (e.g. read or written to). |
QFileDevice::FileBirthTime | 1 | When the file was created (may not be not supported on UNIX). |
QFileDevice::FileMetadataChangeTime | 2 | When the file's metadata was last changed. |
QFileDevice::FileModificationTime | 3 | When the file was most recently modified. |
This enum was introduced or modified in Qt 5.10.
See also setFileTime(), fileTime(), and QFileInfo::fileTime().
enum QFileDevice::MemoryMapFlags
This enum describes special options that may be used by the map() function.
| Constant | Value | Description |
|---|---|---|
QFileDevice::NoOptions | 0 | No options. |
QFileDevice::MapPrivateOption | 0x0001 | The mapped memory will be private, so any modifications will not be visible to other processes and will not be written to disk. Any such modifications will be lost when the memory is unmapped. It is unspecified whether modifications made to the file made after the mapping is created will be visible through the mapped memory. This enum value was introduced in Qt 5.4. |
This enum was introduced or modified in Qt 4.4.
enum QFileDevice::Permission
This enum is used by the permission() function to report the permissions and ownership of a file. The values may be OR-ed together to test multiple permissions and ownership values.
| Constant | Value | Description |
|---|---|---|
QFileDevice::ReadOwner | 0x4000 | The file is readable by the owner of the file. |
QFileDevice::WriteOwner | 0x2000 | The file is writable by the owner of the file. |
QFileDevice::ExeOwner | 0x1000 | The file is executable by the owner of the file. |
QFileDevice::ReadUser | 0x0400 | The file is readable by the user. |
QFileDevice::WriteUser | 0x0200 | The file is writable by the user. |
QFileDevice::ExeUser | 0x0100 | The file is executable by the user. |
QFileDevice::ReadGroup | 0x0040 | The file is readable by the group. |
QFileDevice::WriteGroup | 0x0020 | The file is writable by the group. |
QFileDevice::ExeGroup | 0x0010 | The file is executable by the group. |
QFileDevice::ReadOther | 0x0004 | The file is readable by anyone. |
QFileDevice::WriteOther | 0x0002 | The file is writable by anyone. |
QFileDevice::ExeOther | 0x0001 | The file is executable by anyone. |
Warning: Because of differences in the platforms supported by Qt, the semantics of ReadUser, WriteUser and ExeUser are platform-dependent: On Unix, the rights of the owner of the file are returned and on Windows the rights of the current user are returned. This behavior might change in a future Qt version.
Note: On NTFS file systems, ownership and permissions checking is disabled by default for performance reasons. To enable it, include the following line:
extern Q_CORE_EXPORT int qt_ntfs_permission_lookup;
Permission checking is then turned on and off by incrementing and decrementing qt_ntfs_permission_lookup by 1.
qt_ntfs_permission_lookup++; // turn checking on qt_ntfs_permission_lookup--; // turn it off again