tolower—translate characters to lowercase #include <ctype.h>
int tolower(int c);
int _tolower(int c);
Description
tolower is a macro which converts uppercase characters to lowercase,
leaving all other characters unchanged. It is only defined when
c is an integer in the range EOF to 255.
You can use a compiled subroutine instead of the macro definition by
undefining this macro using `#undef tolower'.
_tolower performs the same conversion as tolower, but should
only be used when c is known to be an uppercase character (A–Z).
Returns
tolower returns the lowercase equivalent of c when it is a
character between A and Z, and c otherwise.
_tolower returns the lowercase equivalent of c when it is a
character between A and Z. If c is not one of these
characters, the behaviour of _tolower is undefined.
Portability
tolower is ANSI C. _tolower is not recommended for portable
programs.
No supporting OS subroutines are required.