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(libc.info)Wide Character Case Conversion

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Mapping of wide characters.
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   The classification functions are also generalized by the ISO C
standard.  Instead of just allowing the two standard mappings, a locale
can contain others.  Again, the `localedef' program already supports
generating such locale data files.

 - Data Type: wctrans_t
     This data type is defined as a scalar type which can hold a value
     representing the locale-dependent character mapping.  There is no
     way to construct such a value apart from using the return value of
     the `wctrans' function.

     This type is defined in `wctype.h'.

 - Function: wctrans_t wctrans (const char *PROPERTY)
     The `wctrans' function has to be used to find out whether a named
     mapping is defined in the current locale selected for the
     `LC_CTYPE' category.  If the returned value is non-zero, you can
     use it afterwards in calls to `towctrans'.  If the return value is
     zero no such mapping is known in the current locale.

     Beside locale-specific mappings there are two mappings which are
     guaranteed to be available in every locale:

     `"tolower"'                        `"toupper"'

     These functions are declared in `wctype.h'.

 - Function: wint_t towctrans (wint_t WC, wctrans_t DESC)
     `towctrans' maps the input character WC according to the rules of
     the mapping for which DESC is a descriptor, and returns the value
     it finds.  DESC must be obtained by a successful call to `wctrans'.

     This function is declared in `wctype.h'.

   For the generally available mappings, the ISO C standard defines
convenient shortcuts so that it is not necessary to call `wctrans' for
them.

 - Function: wint_t towlower (wint_t WC)
     If WC is an upper-case letter, `towlower' returns the corresponding
     lower-case letter.  If WC is not an upper-case letter, WC is
     returned unchanged.

     `towlower' can be implemented using

          towctrans (wc, wctrans ("tolower"))

     This function is declared in `wctype.h'.

 - Function: wint_t towupper (wint_t WC)
     If WC is a lower-case letter, `towupper' returns the corresponding
     upper-case letter.  Otherwise WC is returned unchanged.

     `towupper' can be implemented using

          towctrans (wc, wctrans ("toupper"))

     This function is declared in `wctype.h'.

   The same warnings given in the last section for the use of the wide
character classification functions apply here.  It is not possible to
simply cast a `char' type value to a `wint_t' and use it as an argument
to `towctrans' calls.