- Qt 5.15
- Qt Core
- C++ Classes
- QMimeDatabase
- Qt 5.15.18 Reference Documentation

# QMimeDatabase Class

The QMimeDatabase class maintains a database of MIME types. More...

Header: | #include <QMimeDatabase>
qmake: | QT += core
Since: | Qt 5.0

This class was introduced in Qt 5.0.

- List of all members, including inherited members

Note: All functions in this class are thread-safe.

## Public Types

enum | MatchMode { MatchDefault, MatchExtension, MatchContent }

## Public Functions

| QMimeDatabase()
| ~QMimeDatabase()
QList<QMimeType> | allMimeTypes() const
QMimeType | mimeTypeForData(const QByteArray &data) const
QMimeType | mimeTypeForData(QIODevice *device) const
QMimeType | mimeTypeForFile(const QFileInfo &fileInfo, MatchMode mode = MatchDefault) const
QMimeType | mimeTypeForFile(const QString &fileName, MatchMode mode = MatchDefault) const
QMimeType | mimeTypeForFileNameAndData(const QString &fileName, QIODevice *device) const
QMimeType | mimeTypeForFileNameAndData(const QString &fileName, const QByteArray &data) const
QMimeType | mimeTypeForName(const QString &nameOrAlias) const
QMimeType | mimeTypeForUrl(const QUrl &url) const
QList<QMimeType> | mimeTypesForFileName(const QString &fileName) const
QString | suffixForFileName(const QString &fileName) const

## Detailed Description

The MIME type database is provided by the freedesktop.org shared-mime-info project. If the MIME type database cannot be found on the system, as is the case on most Windows, macOS, and iOS systems, Qt will use its own copy of it.

Applications which want to define custom MIME types need to install an XML file into the locations searched for MIME definitions. These locations can be queried with

     QStandardPaths::locateAll(QStandardPaths::GenericDataLocation, QLatin1String("mime/packages"),
                               QStandardPaths::LocateDirectory);

On a typical Unix system, this will be /usr/share/mime/packages/, but it is also possible to extend the list of directories by setting the environment variable `XDG_DATA_DIRS`. For instance adding /opt/myapp/share to `XDG_DATA_DIRS` will result in /opt/myapp/share/mime/packages/ being searched for MIME definitions.

Here is an example of MIME XML:

     <?xml version="1.0" encoding="UTF-8"?>
     <mime-info xmlns="http://www.freedesktop.org/standards/shared-mime-info">
       <mime-type type="application/vnd.qt.qmakeprofile">
         <comment xml:lang="en">Qt qmake Profile</comment>
         <glob pattern="*.pro" weight="50"/>
       </mime-type>
     </mime-info>

For more details about the syntax of XML MIME definitions, including defining "magic" in order to detect MIME types based on data as well, read the Shared Mime Info specification at http://standards.freedesktop.org/shared-mime-info-spec/shared-mime-info-spec-latest.html

On Unix systems, a binary cache is used for more performance. This cache is generated by the command "update-mime-database path", where path would be /opt/myapp/share/mime in the above example. Make sure to run this command when installing the MIME type definition file.

     QMimeDatabase db;
     QMimeType mime = db.mimeTypeForFile(fileName);
     if (mime.inherits("text/plain")) {
         // The file is plain text, we can display it in a QTextEdit
     }

See also QMimeType and MIME Type Browser Example.

## Member Type Documentation

### enum QMimeDatabase::MatchMode

This enum specifies how matching a file to a MIME type is performed.

Constant | Value | Description
--- | --- | ---
`QMimeDatabase::MatchDefault` | `0x0` | Both the file name and content are used to look for a match
`QMimeDatabase::MatchExtension` | `0x1` | Only the file name is used to look for a match
`QMimeDatabase::MatchContent` | `0x2` | The file content is used to look for a match

## Member Function Documentation

### QMimeDatabase::QMimeDatabase()

Constructs a QMimeDatabase object.

It is perfectly OK to create an instance of QMimeDatabase every time you need to perform a lookup. The parsing of mimetypes is done on demand (when shared-mime-info is installed) or when the very first instance is constructed (when parsing XML files directly).

### QMimeDatabase::~QMimeDatabase()

Destroys the QMimeDatabase object.

### QList<QMimeType> QMimeDatabase::allMimeTypes() const

Returns the list of all available MIME types.

This can be useful for showing all MIME types to the user, for instance in a MIME type editor. Do not use unless really necessary in other cases though, prefer using the mimeTypeForXxx() methods for performance reasons.

### QMimeType QMimeDatabase::mimeTypeForData(const QByteArray &data) const

Returns a MIME type for data.

A valid MIME type is always returned. If data doesn't match any known MIME type data, the default MIME type (application/octet-stream) is returned.

### QMimeType QMimeDatabase::mimeTypeForData(QIODevice *device) const

Returns a MIME type for the data in device.

A valid MIME type is always returned. If the data in device doesn't match any known MIME type data, the default MIME type (application/octet-stream) is returned.

### QMimeType QMimeDatabase::mimeTypeForFile(const QFileInfo &fileInfo, MatchMode mode = MatchDefault) const

Returns a MIME type for fileInfo.

A valid MIME type is always returned.

The default matching algorithm looks at both the file name and the file contents, if necessary. The file extension has priority over the contents, but the contents will be used if the file extension is unknown, or matches multiple MIME types. If fileInfo is a Unix symbolic link, the file that it refers to will be used instead. If the file doesn't match any known pattern or data, the default MIME type (application/octet-stream) is returned.

When mode is set to MatchExtension, only the file name is used, not the file contents. The file doesn't even have to exist. If the file name doesn't match any known pattern, the default MIME type (application/octet-stream) is returned. If multiple MIME types match this file, the first one (alphabetically) is returned.

When mode is set to MatchContent, and the file is readable, only the file contents are used to determine the MIME type. This is equivalent to calling mimeTypeForData with a QFile as input device.

fileInfo may refer to an absolute or relative path.

See also QMimeType::isDefault() and mimeTypeForData().

### QMimeType QMimeDatabase::mimeTypeForFile(const QString &fileName, MatchMode mode = MatchDefault) const

Returns a MIME type for the file named fileName using mode.

This is an overloaded function.

### QMimeType QMimeDatabase::mimeTypeForFileNameAndData(const QString &fileName, QIODevice *device) const

Returns a MIME type for the given fileName and device data.

This overload can be useful when the file is remote, and we started to download some of its data in a device. This allows to do full MIME type matching for remote files as well.

If the device is not open, it will be opened by this function, and closed after the MIME type detection is completed.

A valid MIME type is always returned. If device data doesn't match any known MIME type data, the default MIME type (application/octet-stream) is returned.

This method looks at both the file name and the file contents, if necessary. The file extension has priority over the contents, but the contents will be used if the file extension is unknown, or matches multiple MIME types.

### QMimeType QMimeDatabase::mimeTypeForFileNameAndData(const QString &fileName, const QByteArray &data) const

Returns a MIME type for the given fileName and device data.

This overload can be useful when the file is remote, and we started to download some of its data. This allows to do full MIME type matching for remote files as well.

A valid MIME type is always returned. If data doesn't match any known MIME type data, the default MIME type (application/octet-stream) is returned.

This method looks at both the file name and the file contents, if necessary. The file extension has priority over the contents, but the contents will be used if the file extension is unknown, or matches multiple MIME types.

### QMimeType QMimeDatabase::mimeTypeForName(const QString &nameOrAlias) const

Returns a MIME type for nameOrAlias or an invalid one if none found.

### QMimeType QMimeDatabase::mimeTypeForUrl(const QUrl &url) const

Returns a MIME type for url.

If the URL is a local file, this calls mimeTypeForFile.

Otherwise the matching is done based on the file name only, except for schemes where file names don't mean much, like HTTP. This method always returns the default mimetype for HTTP URLs, use QNetworkAccessManager to handle HTTP URLs properly.

A valid MIME type is always returned. If url doesn't match any known MIME type data, the default MIME type (application/octet-stream) is returned.

### QList<QMimeType> QMimeDatabase::mimeTypesForFileName(const QString &fileName) const

Returns the MIME types for the file name fileName.

If the file name doesn't match any known pattern, an empty list is returned. If multiple MIME types match this file, they are all returned.

This function does not try to open the file. To also use the content when determining the MIME type, use mimeTypeForFile() or mimeTypeForFileNameAndData() instead.

See also mimeTypeForFile().

### QString QMimeDatabase::suffixForFileName(const QString &fileName) const

Returns the suffix for the file fileName, as known by the MIME database.

This allows to pre-select "tar.bz2" for foo.tar.bz2, but still only "txt" for my.file.with.dots.txt.