QResource Class
The QResource class provides an interface for reading directly from resources. More...
| Header: | #include <QResource> |
| CMake: | find_package(Qt6 REQUIRED COMPONENTS Core) target_link_libraries(mytarget PRIVATE Qt6::Core) |
| qmake: | QT += core |
- List of all members, including inherited members
- QResource is part of Input/Output and Networking.
Note: All functions in this class are reentrant.
Public Types
| enum | Compression { NoCompression, ZlibCompression, ZstdCompression } |
Public Functions
| QResource(const QString &file = QString(), const QLocale &locale = QLocale()) | |
| ~QResource() | |
| QString | absoluteFilePath() const |
| QResource::Compression | compressionAlgorithm() const |
| const uchar * | data() const |
| QString | fileName() const |
| bool | isValid() const |
| QDateTime | lastModified() const |
| QLocale | locale() const |
| void | setFileName(const QString &file) |
| void | setLocale(const QLocale &locale) |
| qint64 | size() const |
| QByteArray | uncompressedData() const |
| qint64 | uncompressedSize() const |
Static Public Members
| bool | registerResource(const QString &rccFileName, const QString &mapRoot = QString()) |
| bool | registerResource(const uchar *rccData, const QString &mapRoot = QString()) |
| bool | unregisterResource(const QString &rccFileName, const QString &mapRoot = QString()) |
| bool | unregisterResource(const uchar *rccData, const QString &mapRoot = QString()) |
Protected Functions
Detailed Description
QResource is an object that represents a set of data (and possibly children) relating to a single resource entity. QResource gives direct access to the bytes in their raw format. In this way direct access allows reading data without buffer copying or indirection. Indirection is often useful when interacting with the resource entity as if it is a file, this can be achieved with QFile. The data and children behind a QResource are normally compiled into an application/library, but it is also possible to load a resource at runtime. When loaded at run time the resource file will be loaded as one big set of data and then given out in pieces via references into the resource tree.
A QResource can either be loaded with an absolute path, either treated as a file system rooted with a / character, or in resource notation rooted with a : character. A relative resource can also be opened which will be found in the list of paths returned by QDir::searchPaths().
A QResource that is representing a file will have data backing it, this data can possibly be compressed, in which case qUncompress() must be used to access the real data; this happens implicitly when accessed through a QFile. A QResource that is representing a directory will have only children and no data.
Dynamic Resource Loading
A resource can be left out of an application's binary and loaded when it is needed at run-time by using the registerResource() function. The resource file passed into registerResource() must be a binary resource as created by rcc. Further information about binary resources can be found in The Qt Resource System documentation.
This can often be useful when loading a large set of application icons that may change based on a setting, or that can be edited by a user and later recreated. The resource is immediately loaded into memory, either as a result of a single file read operation, or as a memory mapped file.
This approach can prove to be a significant performance gain as only a single file will be loaded, and pieces of data will be given out via the path requested in setFileName().
The unregisterResource() function removes a reference to a particular file. If there are QResource objects that currently reference resources related to the unregistered file, they will continue to be valid but the resource file itself will be removed from the resource roots, and thus no further QResource can be created pointing into this resource data. The resource itself will be unmapped from memory when the last QResource that points to it is destroyed.
Corruption and Security
The QResource class performs some checks on the file passed to determine whether it is supported by the current version of Qt. Those tests are only to check the file header does not request features (such as Zstandard decompression) that have not been compiled in or that the file is not of a future version of Qt. They do not confirm the validity of the entire file.
QResource should not be used on files whose provenance cannot be trusted. Applications should be designed to attempt to load only resource files whose provenance is at least as trustworthy as that of the application itself or its plugins.
See also The Qt Resource System, QFile, QDir, and QFileInfo.
Member Type Documentation
enum QResource::Compression
This enum is used by compressionAlgorithm() to indicate which algorithm the RCC tool used to compress the payload.
| Constant | Value | Description |
|---|---|---|
QResource::NoCompression | 0 | Contents are not compressed |
QResource::ZlibCompression | 1 | Contents are compressed using zlib and can be decompressed using the qUncompress() function. |
QResource::ZstdCompression | 2 | Contents are compressed using zstd. To decompress, use the ZSTD_decompress function from the zstd library. |
See also compressionAlgorithm().
Member Function Documentation
QResource::QResource(const QString &file = QString(), const QLocale &locale = QLocale())
Constructs a QResource pointing to file. locale is used to load a specific localization of a resource data.
See also QFileInfo, QDir::searchPaths(), setFileName(), and setLocale().
[noexcept] QResource::~QResource()
Releases the resources of the QResource object.
QString QResource::absoluteFilePath() const
Returns the real path that this QResource represents, if the resource was found via the QDir::searchPaths() it will be indicated in the path.
See also fileName().
[protected] QStringList QResource::children() const
Returns a list of all resources in this directory, if the resource represents a file the list will be empty.
See also isDir().
QResource::Compression QResource::compressionAlgorithm() const
Returns the compression type that this resource is compressed with, if any. If it is not compressed, this function returns QResource::NoCompression.
If this function returns QResource::ZlibCompression, you may decompress the data using the qUncompress() function. Up until Qt 5.13, this was the only possible compression algorithm.
If this function returns QResource::ZstdCompression, you need to use the Zstandard library functions (<zstd.h> header). Qt does not provide a wrapper.
See Zstandard manual.
const uchar *QResource::data() const
Returns direct access to a segment of read-only data, that this resource represents. If the resource is compressed, the data returned is also compressed. The caller must then decompress the data or use uncompressedData(). If the resource is a directory, nullptr is returned.
See also uncompressedData(), size(), and isFile().
QString QResource::fileName() const
Returns the full path to the file that this QResource represents as it was passed.
See also setFileName() and absoluteFilePath().
[protected] bool QResource::isDir() const
Returns true if the resource represents a directory and thus may have children() in it, false if it represents a file.
See also isFile().
[protected] bool QResource::isFile() const
Returns true if the resource represents a file and thus has data backing it, false if it represents a directory.
See also isDir().
bool QResource::isValid() const
Returns true if the resource really exists in the resource hierarchy, false otherwise.
QDateTime QResource::lastModified() const
Returns the date and time when the file was last modified before packaging into a resource.
QLocale QResource::locale() const
Returns the locale used to locate the data for the QResource.
See also setLocale().
[static] bool QResource::registerResource(const QString &rccFileName, const QString &mapRoot = QString())
Registers the resource with the given rccFileName at the location in the resource tree specified by mapRoot, and returns true if the file is successfully opened; otherwise returns false.
See also unregisterResource().
[static] bool QResource::registerResource(const uchar *rccData, const QString &mapRoot = QString())
Registers the resource with the given rccData at the location in the resource tree specified by mapRoot, and returns true if the file is successfully opened; otherwise returns false.
Warning: The data must remain valid throughout the life of any QFile that may reference the resource data.
See also unregisterResource().
void QResource::setFileName(const QString &file)
Sets a QResource to point to file. file can either be absolute, in which case it is opened directly, if relative then the file will be tried to be found in QDir::searchPaths().
See also fileName() and absoluteFilePath().
void QResource::setLocale(const QLocale &locale)
Sets a QResource to only load the localization of resource to for locale. If a resource for the specific locale is not found then the C locale is used.
See also locale() and setFileName().
qint64 QResource::size() const
Returns the size of the stored data backing the resource.
If the resource is compressed, this function returns the size of the compressed data. See uncompressedSize() for the uncompressed size.
See also data(), uncompressedSize(), and isFile().
QByteArray QResource::uncompressedData() const
Returns the resource data, decompressing it first, if the data was stored compressed. If the resource is a directory or an error occurs while decompressing, a null QByteArray is returned.
Note: If the data was compressed, this function will decompress every time it is called. The result is not cached between calls.
See also uncompressedSize(), size(), compressionAlgorithm(), and isFile().
qint64 QResource::uncompressedSize() const
Returns the size of the data in this resource. If the data was not compressed, this function returns the same as size(). If it was, then this function extracts the size of the original uncompressed data from the stored stream.
See also size(), uncompressedData(), and isFile().
[static] bool QResource::unregisterResource(const QString &rccFileName, const QString &mapRoot = QString())
Unregisters the resource with the given rccFileName at the location in the resource tree specified by mapRoot, and returns true if the resource is successfully unloaded and no references exist for the resource; otherwise returns false.
See also registerResource().
[static] bool QResource::unregisterResource(const uchar *rccData, const QString &mapRoot = QString())
Unregisters the resource with the given rccData at the location in the resource tree specified by mapRoot, and returns true if the resource is successfully unloaded and no references exist into the resource; otherwise returns false.
See also registerResource().