Conversion from upper-case to lower-case (not converted if argument is not in upper-case)

[Classification]

Standard library

[Syntax]

#include <ctype.h>

int tolower(int c);

[Return value]

If isupper is true with respect to c, returns a character that makes islower true in response; otherwise, returns c.

[Description]

This function is a macro that converts uppercase characters into the corresponding lowercase characters and leaves the other characters unchanged.

This macro is defined only when c is an integer in the range of EOF to 255. A compiled subroutine can be used instead of the macro definition, which is invalidated by using "#undef tolower".