man3/memmem.3

.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
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.\" References consulted:
.\"     Linux libc source code
.\"     386BSD man pages
.\" Modified Sat Jul 24 18:50:48 1993 by Rik Faith (faith@cs.unc.edu)
.\" Interchanged 'needle' and 'haystack'; added history, aeb, 980113.
.TH MEMMEM 3  2021-03-22 "GNU" "Linux Programmer's Manual"
.SH NAME
memmem \- locate a substring
.SH SYNOPSIS
.nf
.BR "#define _GNU_SOURCE" "         /* See feature_test_macros(7) */"
.B #include <string.h>
.PP
.BI "void *memmem(const void *" haystack ", size_t " haystacklen ,
.BI "             const void *" needle ", size_t " needlelen  );
.fi
.SH DESCRIPTION
The
.BR memmem ()
function finds the start of the first occurrence
of the substring
.IR needle
of length
.I needlelen
in the memory
area
.I haystack
of length
.IR haystacklen .
.SH RETURN VALUE
The
.BR memmem ()
function returns a pointer to the beginning of the
substring, or NULL if the substring is not found.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR memmem ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
This function is not specified in POSIX.1,
but is present on a number of other systems.
.SH BUGS
.\" This function was broken in Linux libraries up to and including libc 5.0.9;
.\" there the
.\" .IR needle
.\" and
.\" .I haystack
.\" arguments were interchanged,
.\" and a pointer to the end of the first occurrence of
.\" .I needle
.\" was returned.
.\"
.\" Both old and new libc's have the bug that if
.\" .I needle
.\" is empty,
.\" .I haystack\-1
.\" (instead of
.\" .IR haystack )
.\" is returned.
In glibc 2.0, if
.I needle
is empty,
.BR memmem ()
returns a pointer to the last byte of
.IR haystack .
This is fixed in glibc 2.1.
.SH SEE ALSO
.BR bstring (3),
.BR strstr (3)