tolower, tolower_l - transliterate upper-case characters to lower-case
int tolower(int c);
int tolower_l(int c, locale_t loc);
The tolower() function has as a domain of 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 locale category LC_CTYPE), the result
is the corresponding lower-case letter. All other arguments in the domain are
The function tolower_l() behaves identically to
tolower(), except instead of operating in the current locale, it
operates in the locale specified by loc.
A macro form, _tolower() exists. It is defined for
standards conformance, particularly with legacy standards. It was deprecated
in POSIX 2008 (Issue 7), and its use is discouraged. The macro, on this
system, is just an alias for tolower().
On successful completion, tolower() returns the lower-case letter
corresponding to the argument passed. Otherwise, it returns the argument
See attributes(7) for descriptions of the following attributes: