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`iswcntrl'--wide-character cntrl test

     #include <wctype.h>
     int iswcntrl(wint_t C);
`iswcntrl' is a function which classifies wide-character values that
are categorized as a control character.
`iswcntrl' returns non-zero if C is a control wide-character.
`iswcntrl' is C99.
   No supporting OS subroutines are required.