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QTranslator Class

The QTranslator class provides internationalization support for text output. More...

Header: #include <QTranslator>
qmake: QT += core
Inherits: QObject

Public Functions

QTranslator(QObject * parent = 0)
~QTranslator()
virtual bool isEmpty() const
bool load(const QString & filename, const QString & directory = QString(), const QString & search_delimiters = QString(), const QString & suffix = QString())
bool load(const QLocale & locale, const QString & filename, const QString & prefix = QString(), const QString & directory = QString(), const QString & suffix = QString())
bool load(const uchar * data, int len, const QString & directory = QString())
virtual QString translate(const char * context, const char * sourceText, const char * disambiguation = 0, int n = -1) const
  • 31 public functions inherited from QObject

Additional Inherited Members

  • 1 property inherited from QObject
  • 1 public slot inherited from QObject
  • 2 signals inherited from QObject
  • 11 static public members inherited from QObject
  • 9 protected functions inherited from QObject

Detailed Description

The QTranslator class provides internationalization support for text output.

An object of this class contains a set of translations from a source language to a target language. QTranslator provides functions to look up translations in a translation file. Translation files are created using Qt Linguist.

The most common use of QTranslator is to: load a translation file, install it using QCoreApplication::installTranslator(), and use it via QObject::tr(). Here's an example main() function using the QTranslator:

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QTranslator translator;
    // look up e.g. :/translations/myapp_de.qm
    if (translator.load(QLocale(), QLatin1String("myapp"), QLatin1String("_"), QLatin1String(":/translations")))
        app.installTranslator(&translator);

    QPushButton hello(QCoreApplication::translate("main", "Hello world!"));
    hello.resize(100, 30);

    hello.show();
    return app.exec();
}

Note that the translator must be created before the application's widgets.

Most applications will never need to do anything else with this class. The other functions provided by this class are useful for applications that work on translator files.

Looking up Translations

It is possible to look up a translation using translate() (as tr() and QCoreApplication::translate() do). The translate() function takes up to three parameters:

  • The context - usually the class name for the tr() caller.
  • The source text - usually the argument to tr().
  • The disambiguation - an optional string that helps disambiguate different uses of the same text in the same context.

For example, the "Cancel" in a dialog might have "Anuluj" when the program runs in Polish (in this case the source text would be "Cancel"). The context would (normally) be the dialog's class name; there would normally be no comment, and the translated text would be "Anuluj".

But it's not always so simple. The Spanish version of a printer dialog with settings for two-sided printing and binding would probably require both "Activado" and "Activada" as translations for "Enabled". In this case the source text would be "Enabled" in both cases, and the context would be the dialog's class name, but the two items would have disambiguations such as "two-sided printing" for one and "binding" for the other. The disambiguation enables the translator to choose the appropriate gender for the Spanish version, and enables Qt to distinguish between translations.

Using Multiple Translations

Multiple translation files can be installed in an application. Translations are searched for in the reverse order in which they were installed, so the most recently installed translation file is searched for translations first and the earliest translation file is searched last. The search stops as soon as a translation containing a matching string is found.

This mechanism makes it possible for a specific translation to be "selected" or given priority over the others; simply uninstall the translator from the application by passing it to the QCoreApplication::removeTranslator() function and reinstall it with QCoreApplication::installTranslator(). It will then be the first translation to be searched for matching strings.

See also QCoreApplication::installTranslator(), QCoreApplication::removeTranslator(), QObject::tr(), QCoreApplication::translate(), I18N Example, Hello tr() Example, Arrow Pad Example, and Troll Print Example.

Member Function Documentation

QTranslator::QTranslator(QObject * parent = 0)

Constructs an empty message file object with parent parent that is not connected to any file.

QTranslator::~QTranslator()

Destroys the object and frees any allocated resources.

[virtual] bool QTranslator::isEmpty() const

Returns true if this translator is empty, otherwise returns false. This function works with stripped and unstripped translation files.

bool QTranslator::load(const QString & filename, const QString & directory = QString(), const QString & search_delimiters = QString(), const QString & suffix = QString())

Loads filename + suffix (".qm" if the suffix is not specified), which may be an absolute file name or relative to directory. Returns true if the translation is successfully loaded; otherwise returns false.

If directory is not specified, the current directory is used (i.e., as currentPath()).

The previous contents of this translator object are discarded.

If the file name does not exist, other file names are tried in the following order:

  1. File name without suffix appended.
  2. File name with text after a character in search_delimiters stripped ("_." is the default for search_delimiters if it is an empty string) and suffix.
  3. File name stripped without suffix appended.
  4. File name stripped further, etc.

For example, an application running in the fr_CA locale (French-speaking Canada) might call load("foo.fr_ca", "/opt/foolib"). load() would then try to open the first existing readable file from this list:

  1. /opt/foolib/foo.fr_ca.qm
  2. /opt/foolib/foo.fr_ca
  3. /opt/foolib/foo.fr.qm
  4. /opt/foolib/foo.fr
  5. /opt/foolib/foo.qm
  6. /opt/foolib/foo

Usually, it is better to use the QTranslator::load(const QLocale &, const QString &, const QString &, const QString &, const QString &) function instead, because it uses QLocale::uiLanguages() and not simply the locale name, which refers to the formatting of dates and numbers and not necessarily the UI language.

bool QTranslator::load(const QLocale & locale, const QString & filename, const QString & prefix = QString(), const QString & directory = QString(), const QString & suffix = QString())

Loads filename + prefix + ui language name + suffix (".qm" if the suffix is not specified), which may be an absolute file name or relative to directory. Returns true if the translation is successfully loaded; otherwise returns false.

The previous contents of this translator object are discarded.

If the file name does not exist, other file names are tried in the following order:

  1. File name without suffix appended.
  2. File name with ui language part after a "_" character stripped and suffix.
  3. File name with ui language part stripped without suffix appended.
  4. File name with ui language part stripped further, etc.

For example, an application running in the locale with the following ui languages - "es", "fr-CA", "de" might call load(QLocale(), "foo", ".", "/opt/foolib", ".qm"). load() would replace '-' (dash) with '_' (underscore) in the ui language and then try to open the first existing readable file from this list:

  1. /opt/foolib/foo.es.qm
  2. /opt/foolib/foo.es
  3. /opt/foolib/foo.fr_CA.qm
  4. /opt/foolib/foo.fr_CA
  5. /opt/foolib/foo.de.qm
  6. /opt/foolib/foo.de
  7. /opt/foolib/foo.fr.qm
  8. /opt/foolib/foo.fr
  9. /opt/foolib/foo.qm
  10. /opt/foolib/foo.
  11. /opt/foolib/foo

On operating systems where file system is case sensitive, QTranslator also tries to load a lower-cased version of the locale name.

This function was introduced in Qt 4.8.

bool QTranslator::load(const uchar * data, int len, const QString & directory = QString())

This function overloads load().

Loads the QM file data data of length len into the translator.

The data is not copied. The caller must be able to guarantee that data will not be deleted or modified.

directory is only used to specify the base directory when loading the dependencies of a QM file. If the file does not have dependencies, this argument is ignored.

[virtual] QString QTranslator::translate(const char * context, const char * sourceText, const char * disambiguation = 0, int n = -1) const

Returns the translation for the key (context, sourceText, disambiguation). If none is found, also tries (context, sourceText, ""). If that still fails, returns a null string.

Note: Incomplete translations may result in unexpected behavior: If no translation for (context, sourceText, "") is provided, the method might in this case actually return a translation for a different disambiguation.

If n is not -1, it is used to choose an appropriate form for the translation (e.g. "%n file found" vs. "%n files found").

If you need to programatically insert translations into a QTranslator, this function can be reimplemented.

See also load().

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