The tolower() function has as a domain a type int, the value of which is representable as an unsigned char or the value of EOF. If the argument has any other value, the argument is returned unchanged. If the argument of tolower() represents an upper-case letter, and there exists a corresponding lower-case letter (as defined by character type information in the program locale category LC_CTYPE), the result is the corresponding lower-case letter. All other arguments in the domain are returned unchanged.

On successful completion, tolower() returns the lower-case letter corresponding to the argument passed. Otherwise, it returns the argument unchanged.

No errors are defined.

See attributes(5) for descriptions of the following attributes:

_tolower(3C), setlocale(3C), attributes(5)