(gettext.info)Contexts

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Enter node , (file) or (file)node

11.2.5 Using contexts for solving ambiguities
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   One place where the ‘gettext’ functions, if used normally, have big
problems is within programs with graphical user interfaces (GUIs).  The
problem is that many of the strings which have to be translated are very
short.  They have to appear in pull-down menus which restricts the
length.  But strings which are not containing entire sentences or at
least large fragments of a sentence may appear in more than one
situation in the program but might have different translations.  This is
especially true for the one-word strings which are frequently used in
GUI programs.

   As a consequence many people say that the ‘gettext’ approach is wrong
and instead ‘catgets’ should be used which indeed does not have this
problem.  But there is a very simple and powerful method to handle this
kind of problems with the ‘gettext’ functions.

   Contexts can be added to strings to be translated.  A context
dependent translation lookup is when a translation for a given string is
searched, that is limited to a given context.  The translation for the
same string in a different context can be different.  The different
translations of the same string in different contexts can be stored in
the in the same MO file, and can be edited by the translator in the same
PO file.

   The ‘gettext.h’ include file contains the lookup macros for strings
with contexts.  They are implemented as thin macros and inline functions
over the functions from ‘<libintl.h>’.

     const char *pgettext (const char *msgctxt, const char *msgid);

   In a call of this macro, MSGCTXT and MSGID must be string literals.
The macro returns the translation of MSGID, restricted to the context
given by MSGCTXT.

   The MSGCTXT string is visible in the PO file to the translator.  You
should try to make it somehow canonical and never changing.  Because
every time you change an MSGCTXT, the translator will have to review the
translation of MSGID.

   Finding a canonical MSGCTXT string that doesn’t change over time can
be hard.  But you shouldn’t use the file name or class name containing
the ‘pgettext’ call – because it is a common development task to rename
a file or a class, and it shouldn’t cause translator work.  Also you
shouldn’t use a comment in the form of a complete English sentence as
MSGCTXT – because orthography or grammar changes are often applied to
such sentences, and again, it shouldn’t force the translator to do a
review.

   The ‘p’ in ‘pgettext’ stands for “particular”: ‘pgettext’ fetches a
particular translation of the MSGID.

     const char *dpgettext (const char *domain_name,
                            const char *msgctxt, const char *msgid);
     const char *dcpgettext (const char *domain_name,
                             const char *msgctxt, const char *msgid,
                             int category);

   These are generalizations of ‘pgettext’.  They behave similarly to
‘dgettext’ and ‘dcgettext’, respectively.  The DOMAIN_NAME argument
defines the translation domain.  The CATEGORY argument allows to use
another locale category than ‘LC_MESSAGES’.

   As as example consider the following fictional situation.  A GUI
program has a menu bar with the following entries:

     +------------+------------+--------------------------------------+
     | File       | Printer    |                                      |
     +------------+------------+--------------------------------------+
     | Open     | | Select   |
     | New      | | Open     |
     +----------+ | Connect  |
                  +----------+

   To have the strings ‘File’, ‘Printer’, ‘Open’, ‘New’, ‘Select’, and
‘Connect’ translated there has to be at some point in the code a call to
a function of the ‘gettext’ family.  But in two places the string passed
into the function would be ‘Open’.  The translations might not be the
same and therefore we are in the dilemma described above.

   What distinguishes the two places is the menu path from the menu root
to the particular menu entries:

     Menu|File
     Menu|Printer
     Menu|File|Open
     Menu|File|New
     Menu|Printer|Select
     Menu|Printer|Open
     Menu|Printer|Connect

   The context is thus the menu path without its last part.  So, the
calls look like this:

     pgettext ("Menu|", "File")
     pgettext ("Menu|", "Printer")
     pgettext ("Menu|File|", "Open")
     pgettext ("Menu|File|", "New")
     pgettext ("Menu|Printer|", "Select")
     pgettext ("Menu|Printer|", "Open")
     pgettext ("Menu|Printer|", "Connect")

   Whether or not to use the ‘|’ character at the end of the context is
a matter of style.

   For more complex cases, where the MSGCTXT or MSGID are not string
literals, more general macros are available:

     const char *pgettext_expr (const char *msgctxt, const char *msgid);
     const char *dpgettext_expr (const char *domain_name,
                                 const char *msgctxt, const char *msgid);
     const char *dcpgettext_expr (const char *domain_name,
                                  const char *msgctxt, const char *msgid,
                                  int category);

   Here MSGCTXT and MSGID can be arbitrary string-valued expressions.
These macros are more general.  But in the case that both argument
expressions are string literals, the macros without the ‘_expr’ suffix
are more efficient.