WCTRANS(3) Linux Programmer's Manual WCTRANS(3)

wctrans - wide-character translation mapping

#include <wctype.h>
wctrans_t wctrans(const char *name);

The wctrans_t type represents a mapping which can map a wide character to another wide character. Its nature is implementation-dependent, but the special value (wctrans_t) 0 denotes an invalid mapping. Nonzero wctrans_t values can be passed to the towctrans(3) function to actually perform the wide-character mapping.
The wctrans() function returns a mapping, given by its name. The set of valid names depends on the LC_CTYPE category of the current locale, but the following names are valid in all locales.
    "tolower" - realizes the  tolower(3) mapping
    "toupper" - realizes the  toupper(3) mapping

The wctrans() function returns a mapping descriptor if the name is valid. Otherwise, it returns (wctrans_t) 0.

For an explanation of the terms used in this section, see attributes(7).
Interface Attribute Value
wctrans () Thread safety MT-Safe locale

POSIX.1-2001, POSIX.1-2008, C99.

The behavior of wctrans() depends on the LC_CTYPE category of the current locale.

towctrans(3)
2015-08-08 GNU