.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
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.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
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.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sat Jul 24 17:56:43 1993 by Rik Faith (faith@cs.unc.edu)
.\" Added history, aeb, 980113.
.\" 2005-05-05 mtk: added strcasestr()
.\"
.TH STRSTR 3  2005-04-05 "GNU" "Linux Programmer's Manual"
.SH NAME
strstr, strcasestr \- locate a substring
.SH SYNOPSIS
.nf
.B #include <string.h>
.sp
.BI "char *strstr(const char *" haystack ", const char *" needle );
.sp
.B #define _GNU_SOURCE
.sp
.B #include <string.h>
.sp
.BI "char *strcasestr(const char *" haystack ", const char *" needle );
.fi
.SH DESCRIPTION
The
.BR strstr ()
function finds the first occurrence of the substring
\fIneedle\fP in the string \fIhaystack\fP.
The terminating \(aq\\0\(aq characters are not compared.

The
.BR strcasestr ()
function is like
.BR strstr (),
but ignores the case of both arguments.
.SH "RETURN VALUE"
These functions return a pointer to the beginning of the
substring, or NULL if the substring is not found.
.SH "CONFORMING TO"
The
.BR strstr ()
function conforms to C89 and C99.
The
.BR strcasestr ()
function is a non-standard extension.
.SH BUGS
Early versions of Linux libc (like 4.5.26) would not allow
an empty \fIneedle\fP argument for
.BR strstr ().
Later versions (like 4.6.27) work correctly,
and return \fIhaystack\fP when \fIneedle\fP is empty.
.SH "SEE ALSO"
.BR index (3),
.BR memchr (3),
.BR rindex (3),
.BR strcasecmp (3),
.BR strchr (3),
.BR strpbrk (3),
.BR strsep (3),
.BR strspn (3),
.BR strtok (3),
.BR wcsstr (3),
.BR feature_test_macros (7)
.SH COLOPHON
This page is part of release 3.22 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
