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3.11 isupper, isupper_l—uppercase character predicate

Synopsis 

     #include <ctype.h>
     int isupper(int c);
     
     #include <ctype.h>
     int isupper_l(int c, locale_t locale);

Description
isupper is a macro which classifies singlebyte charset values by table lookup. It is a predicate returning non-zero for uppercase letters (A–Z), and 0 for other characters.

isupper_l is like isupper but performs the check based on the locale specified by the locale object locale. If locale is LC_GLOBAL_LOCALE or not a valid locale object, the behaviour is undefined.

You can use a compiled subroutine instead of the macro definition by undefining the macro using `#undef isupper' or `#undef isupper_l'.
Returns
isupper, isupper_l return non-zero if c is an uppercase letter.
Portability
isupper is ANSI C. isupper_l is POSIX-1.2008.

No supporting OS subroutines are required.