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isalnum
[alphanumeric character predicate]

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

DESCRIPTION
isalnum is a macro which classifies ASCII integer values by table lookup. It is a predicate returning non-zero for alphabetic or numeric ASCII characters, and 0 for other arguments. It is defined for all integer values.

You can use a compiled subroutine instead of the macro definition by undefining the macro, using #undef isalnum.

RETURNS
isalnum returns non-zero if c is a letter (a–z or A–Z) or a digit (0–9).

COMPLIANCE
isalnum is ANSI C.

No OS subroutines are required.