3.1 isalnum, isalnum_l—alphanumeric character predicate

Synopsis

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

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

Description
isalnum is a macro which classifies singlebyte charset 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 only if c is representable as an unsigned char or if c is EOF.

isalnum_l is like isalnum 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 isalnum’ or ‘#undef isalnum_l’.

Returns
isalnum,isalnum_l return non-zero if c is a letter or a digit.

Portability
isalnum is ANSI C. isalnum_l is POSIX-1.2008.

No OS subroutines are required.