3.13 tolower—translate characters to lowercase

Synopsis

     #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.