.\" Copyright (c) 2005 Pascal Gloor <pascal.gloor@spale.com>
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. The name of the author may not be used to endorse or promote
.\"    products derived from this software without specific prior written
.\"    permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd June 29, 2023
.Dt MEMMEM 3
.Os
.Sh NAME
.Nm memmem
.Nd "locate a byte substring in a byte string"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In string.h
.Ft "void *"
.Fo memmem
.Fa "const void *big" "size_t big_len"
.Fa "const void *little" "size_t little_len"
.Fc
.Sh DESCRIPTION
The
.Fn memmem
function
locates the first occurrence of the byte string
.Fa little
in the byte string
.Fa big .
.Sh RETURN VALUES
If
.Fa little_len
is zero
.Fa big
is returned (that is, an empty little is deemed to match at the beginning of
big);
if
.Fa little
occurs nowhere in
.Fa big ,
.Dv NULL
is returned;
otherwise a pointer to the first character of the first occurrence of
.Fa little
is returned.
.Sh SEE ALSO
.Xr memchr 3 ,
.Xr strchr 3 ,
.Xr strstr 3
.Sh STANDARDS
.Fn memmem
conforms to
.St -p1003.1-2024 .
.Sh HISTORY
The
.Fn memmem
function first appeared in
.Fx 6.0 .
It was replaced with an optimized O(n) implementation from the musl libc
project in
.Fx 12.0 .
.An Pascal Gloor Aq Mt pascal.gloor@spale.com
provided this man page along with the previous implementation.
.Sh BUGS
This function was broken in Linux libc up to and including version 5.0.9
and in GNU libc prior to version 2.1.
Prior to
.Fx 11.0
.Nm
returned
.Dv NULL
when
.Fa little_len
equals 0.