3.2 isalpha, isalpha_l—alphabetic character predicate

Synopsis

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

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

Description
isalpha is a macro which classifies singlebyte charset values by table lookup. It is a predicate returning non-zero when c represents an alphabetic ASCII character, and 0 otherwise. It is defined only if c is representable as an unsigned char or if c is EOF.

isalpha_l is like isalpha 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 isalpha’ or ‘#undef isalpha_l’.

Returns
isalpha, isalpha_l return non-zero if c is a letter.

Portability
isalpha is ANSI C. isalpha_l is POSIX-1.2008.

No supporting OS subroutines are required.