isalnum---alphanumeric character predicate#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).
Portability
isalnum is ANSI C.
No OS subroutines are required.