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.Dd $Mdocdate: September 11 2022 $
.Dt TOLOWER 3
.Os
.Sh NAME
.Nm tolower ,
.Nm tolower_l ,
.Nm _tolower
.Nd upper case to lower case letter conversion
.Sh SYNOPSIS
.In ctype.h
.Ft int
.Fn tolower "int c"
.Ft int
.Fn tolower_l "int c" "locale_t locale"
.Ft int
.Fn _tolower "int c"
.Sh DESCRIPTION
The
.Fn tolower
and
.Fn tolower_l
functions convert an upper-case letter to the corresponding lower-case
letter.
The
.Fn _tolower
function is identical to
.Fn tolower
except that
.Fa c
must be an upper-case letter.
.Pp
.Ox
always uses the C locale for these functions,
ignoring the global locale, the thread-specific locale, and the
.Fa locale
argument.
.Sh RETURN VALUES
If the argument to the
.Fn tolower
or
.Fn tolower_l
function is an upper-case letter, the corresponding lower-case letter
is returned if there is one; otherwise the argument is returned unchanged.
If the argument to the
.Fn _tolower
function is an upper-case letter, the corresponding lower-case letter
is returned; otherwise the output is undefined.
.Sh ENVIRONMENT
On systems supporting non-ASCII single-byte character encodings,
the results of
.Fn tolower
and
.Fn _tolower
may depend on the
.Ev LC_CTYPE
.Xr locale 1 .
.Sh SEE ALSO
.Xr isalnum 3 ,
.Xr isalpha 3 ,
.Xr isascii 3 ,
.Xr isblank 3 ,
.Xr iscntrl 3 ,
.Xr isdigit 3 ,
.Xr isgraph 3 ,
.Xr islower 3 ,
.Xr isprint 3 ,
.Xr ispunct 3 ,
.Xr isspace 3 ,
.Xr isupper 3 ,
.Xr isxdigit 3 ,
.Xr stdio 3 ,
.Xr toascii 3 ,
.Xr toupper 3 ,
.Xr towlower 3 ,
.Xr ascii 7
.Sh STANDARDS
The
.Fn tolower
and
.Fn _tolower
functions conform to
.St -ansiC ,
and
.Fn tolower_l
to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn tolower
function first appeared in
.At v7
and acquired the current semantics in
.At III ,
where
.Fn _tolower
first appeared.
.Pp
The
.Fn tolower_l
function has been available since
.Ox 6.2 .
.Sh CAVEATS
The argument
.Fa c
must be
.Dv EOF
or representable as an
.Vt unsigned char ;
otherwise, the result is undefined.