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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\example hellotr
\ingroup examples-linguist
\examplecategory {Internationalization}
\title Hello tr() Example
\brief Translating a small Hello World program to Latin.
The screenshot shows the English version.
\image linguist-hellotr_en.png
See the \l{Qt Linguist Manual} for more information about
translating Qt application.
\section1 Line by Line Walkthrough
\snippet hellotr/main.cpp 0
This line includes the definition of the QTranslator class.
Objects of this class provide translations for user-visible text.
\snippet hellotr/main.cpp 5
Creates a QTranslator object without a parent.
\snippet hellotr/main.cpp 6
Tries to load a file called \c hellotr_la.qm (the \c .qm file extension is
implicit) that contains Latin translations for the source texts used in
the program. No error will occur if the file is not found.
\snippet hellotr/main.cpp 7
Adds the translations from \c hellotr_la.qm to the pool of translations used
by the program.
\snippet hellotr/main.cpp 8
Creates a push button that displays "Hello world!". If \c hellotr_la.qm
was found and contains a translation for "Hello world!", the
translation appears; if not, the source text appears.
All classes that inherit QObject have a \c tr() function. Inside
a member function of a QObject class, we simply write \c tr("Hello
world!") instead of \c QPushButton::tr("Hello world!") or \c
QObject::tr("Hello world!").
\section1 Running the Application in English
Since we haven't made the translation file \c hellotr_la.qm, the source text
is shown when we run the application:
\image linguist-hellotr_en.png
\section1 Creating a Latin Message File
The first step is to create a project file that lists
all the source files for the project.
When using qmake, the relevant lines in \c hellotr.pro are:
\snippet hellotr/hellotr.pro 0
\snippet hellotr/hellotr.pro 1
\c TRANSLATIONS specifies the message files we want to
maintain. In this example, we just maintain one set of translations,
namely Latin.
When using CMake, the relevant lines in \c CMakeLists.txt are:
\snippet hellotr/CMakeLists.txt 0
\codeline
\snippet hellotr/CMakeLists.txt 1
Note that the file extension is \c .ts, not \c .qm. The \c .ts
translation source format is designed for use during the
application's development. Programmers or release managers run
the \c lupdate program to generate and update TS files with
the source text that is extracted from the source code.
Translators read and update the TS files using \e {Qt
Linguist} adding and editing their translations.
The TS format is human-readable XML that can be emailed directly
and is easy to put under version control. If you edit this file
manually, be aware that the default encoding for XML is UTF-8, not
Latin1 (ISO 8859-1). One way to type in a Latin1 character such as
'\oslash' (Norwegian o with slash) is to use an XML entity:
"\ø". This will work for any Unicode 4.0 character.
Once the translations are complete the \c lrelease program is used to
convert the TS files into the QM Qt message file format. The
QM format is a compact binary format designed to deliver very
fast lookup performance. Both \c lupdate and \c lrelease read all the
project's source and header files (as specified in the HEADERS and
SOURCES lines of the project file) and extract the strings that
appear in \c tr() function calls.
\c lupdate is used to create and update the message files (\c hellotr_la.ts
in this case) to keep them in sync with the source code. It is safe to
run \c lupdate at any time, as \c lupdate does not remove any
information.
Try running \c lupdate right now.
When using qmake, \c lupdate must be run manually:
\snippet doc/snippets/doc_src_examples_hellotr.qdoc 0
(The \c -verbose option instructs \c lupdate to display messages that
explain what it is doing.)
When using CMake, build the \c update_translations target to run \c lupdate:
\snippet doc/snippets/doc_src_examples_hellotr.qdoc 5
You should now have a file \c hellotr_la.ts in
the current directory, containing this:
\snippet doc/snippets/doc_src_examples_hellotr.qdoc 1
You don't need to understand the file format since it is read and
updated using tools (\c lupdate, \e {Qt Linguist}, \c lrelease).
\section1 Translating to Latin with Qt Linguist
We will use \e {Qt Linguist} to provide the translation, although
you can use any XML or plain text editor to enter a translation into a
TS file.
To start \e {Qt Linguist}, type
\snippet doc/snippets/doc_src_examples_hellotr.qdoc 2
You should now see the text "QPushButton" in the top left pane.
Double-click it, then click on "Hello world!" and enter "Orbis, te
saluto!" in the \uicontrol Translation pane (the middle right of the
window). Don't forget the exclamation mark!
Click the \uicontrol Done checkbox and choose \uicontrol File|Save from the
menu bar. The TS file will no longer contain
\snippet doc/snippets/doc_src_examples_hellotr.qdoc 3
but instead will have
\snippet doc/snippets/doc_src_examples_hellotr.qdoc 4
\section1 Running the Application in Latin
To see the application running in Latin, we have to generate a QM
file from the TS file. Generating a QM file can be achieved
either from within \e {Qt Linguist} (for a single TS file), or
by using the command line program \c lrelease which will produce one
QM file for each of the TS files listed in the project file.
Generate \c hellotr_la.qm from \c hellotr_la.ts by choosing
\uicontrol File|Release from \e {Qt Linguist}'s menu bar and pressing
\uicontrol Save in the file save dialog that pops up. Now run the \c hellotr
program again. This time the button will be labelled "Orbis, te
saluto!".
\image linguist-hellotr_la.png
*/
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