ISLOWER(3) Library Functions Manual ISLOWER(3)

islower
lower-case character test

Standard C Library (libc, -lc)

#include <ctype.h>

int
islower(int c);

The islower() function tests for any lower-case letter for which none of iscntrl(3), isdigit(3), ispunct(3), or isspace(3) is true. In the ``C'' locale, islower() returns true only for the characters defined as lower-case letters.

The islower() function returns zero if the character tests false and returns non-zero if the character tests true.

ctype(3), isalnum(3), isalpha(3), isascii(3), isblank(3), iscntrl(3), isdigit(3), isgraph(3), isprint(3), ispunct(3), isspace(3), isupper(3), isxdigit(3), stdio(3), toascii(3), tolower(3), toupper(3), ascii(7)

The islower() function conforms to ANSI X3.159-1989 (“ANSI C89”).

The argument to islower() must be EOF or representable as an unsigned char; otherwise, the behavior is undefined. See the CAVEATS section of ctype(3) for more details.
April 17, 2008 NetBSD 9.2