libc.info: isupper

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`isupper'--uppercase character predicate

*Synopsis*
     #include <ctype.h>
     int isupper(int C);
   *Description*
`isupper' is a macro which classifies ASCII integer values by table
lookup.  It is a predicate returning non-zero for upper-case letters
(`A'-`Z'), and 0 for other characters.  It is defined only when
`isascii'(C) is true or C is EOF.
   You can use a compiled subroutine instead of the macro definition by
undefining the macro using ``#undef isupper''.
*Returns*
`isupper' returns non-zero if C is a upper case letter (A-Z).
*Portability*
`isupper' is ANSI C.
   No supporting OS subroutines are required.