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| <!-- %MENU% How to make the program speak the user's language --> |
| <h2 class="chapter">8 Message Translation</h2> |
| |
| <p>The program's interface with the human should be designed in a way to |
| ease the human the task. One of the possibilities is to use messages in |
| whatever language the user prefers. |
| |
| <p>Printing messages in different languages can be implemented in different |
| ways. One could add all the different languages in the source code and |
| add among the variants every time a message has to be printed. This is |
| certainly no good solution since extending the set of languages is |
| difficult (the code must be changed) and the code itself can become |
| really big with dozens of message sets. |
| |
| <p>A better solution is to keep the message sets for each language are kept |
| in separate files which are loaded at runtime depending on the language |
| selection of the user. |
| |
| <p>The GNU C Library provides two different sets of functions to support |
| message translation. The problem is that neither of the interfaces is |
| officially defined by the POSIX standard. The <code>catgets</code> family of |
| functions is defined in the X/Open standard but this is derived from |
| industry decisions and therefore not necessarily based on reasonable |
| decisions. |
| |
| <p>As mentioned above the message catalog handling provides easy |
| extendibility by using external data files which contain the message |
| translations. I.e., these files contain for each of the messages used |
| in the program a translation for the appropriate language. So the tasks |
| of the message handling functions are |
| |
| <ul> |
| <li>locate the external data file with the appropriate translations. |
| <li>load the data and make it possible to address the messages |
| <li>map a given key to the translated message |
| </ul> |
| |
| <p>The two approaches mainly differ in the implementation of this last |
| step. The design decisions made for this influences the whole rest. |
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| <ul class="menu"> |
| <li><a accesskey="1" href="Message-catalogs-a-la-X_002fOpen.html#Message-catalogs-a-la-X_002fOpen">Message catalogs a la X/Open</a>: The <code>catgets</code> family of functions. |
| <li><a accesskey="2" href="The-Uniforum-approach.html#The-Uniforum-approach">The Uniforum approach</a>: The <code>gettext</code> family of functions. |
| </ul> |
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