'\" t
.\" Copyright 1993, David Metcalfe <david@prism.demon.co.uk>
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH strstr 3 2026-08-10 "Linux man-pages 6.19"
.SH NAME
strstr \- string search substring
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.B #include <string.h>
.P
.BI "char *strstr(const char *" haystack ", const char *" needle );
.fi
.SH DESCRIPTION
.BR strstr ()
finds the first occurrence of the substring
.I needle
in the string
.IR haystack .
.P
The terminating null bytes (\[aq]\[rs]0\[aq]) are not compared.
.P
It is equivalent to
.P
.in +4n
.EX
memmem(haystack, strlen(haystack), needle, strlen(needle))
.EE
.in
.SH RETURN VALUE
.BR strstr (3)
returns a pointer to the beginning of the
located substring, or NULL if the substring is not found.
.P
If
.I needle
is the empty string,
the return value is always
.I haystack
itself.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR strstr ()
T}	Thread safety	MT-Safe
.TE
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
POSIX.1-2001, C89.
.SH SEE ALSO
.BR strcasestr (3),
.BR strchr (3),
.BR string (3),
.BR strpbrk (3),
.BR strsep (3),
.BR strspn (3),
.BR wcsstr (3)