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.Dd March 30, 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 CONFORMING TO
.Fn memmem
started as a GNU extension but is now available in at least
the GNU, musl, bionic, OpenBSD, NetBSD, macOS, and Illumos C runtime libraries.
.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.