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3.6 isdigit—decimal digit predicate

Synopsis

#include <ctype.h>
int isdigit(int c);

Description
isdigit is a macro which classifies ASCII integer values by table lookup. It is a predicate returning non-zero for decimal digits, and 0 for other characters. It is defined only if c is representable as an unsigned char or if c is EOF.

You can use a compiled subroutine instead of the macro definition by undefining the macro using ‘#undef isdigit’.


Returns
isdigit returns non-zero if c is a decimal digit (09).


Portability
isdigit is ANSI C.

No supporting OS subroutines are required.