3.7 islower, islower_l—lowercase character predicate

Synopsis

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

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

Description
islower is a macro which classifies singlebyte charset values by table lookup. It is a predicate returning non-zero for minuscules (lowercase alphabetic characters), and 0 for other characters. It is defined only if c is representable as an unsigned char or if c is EOF.

islower_l is like islower 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 islower’ or ‘#undef islower_l’.

Returns
islower, islower_l return non-zero if c is a lowercase letter.

Portability
islower is ANSI C. islower_l is POSIX-1.2008.

No supporting OS subroutines are required.