.\" Copyright (c) 2001 Mike Barcroft <mike@FreeBSD.org>
.\" Copyright (c) 1990, 1991, 1993
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.\" This code is derived from software contributed to Berkeley by
.\" Chris Torek and the American National Standards Committee X3,
.\" on Information Processing Systems.
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.\"     @(#)strstr.3	8.1 (Berkeley) 6/4/93
.\"
.Dd October 11, 2001
.Dt STRSTR 3
.Os
.Sh NAME
.Nm strstr , strcasestr , strnstr
.Nd locate a substring in a string
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In string.h
.Ft char *
.Fn strstr "const char *big" "const char *little"
.Ft char *
.Fn strcasestr "const char *big" "const char *little"
.Ft char *
.Fn strnstr "const char *big" "const char *little" "size_t len"
.In string.h
.In xlocale.h
.Ft char *
.Fn strcasestr_l "const char *big" "const char *little" "locale_t loc"
.Sh DESCRIPTION
The
.Fn strstr
function
locates the first occurrence of the null-terminated string
.Fa little
in the null-terminated string
.Fa big .
.Pp
The
.Fn strcasestr
function is similar to
.Fn strstr ,
but ignores the case of both strings.
.Pp
The
.Fn strcasestr_l
function does the same as
.Fn strcasestr
but takes an explicit locale rather than using the current locale.
.Pp
The
.Fn strnstr
function
locates the first occurrence of the null-terminated string
.Fa little
in the string
.Fa big ,
where not more than
.Fa len
characters are searched.
Characters that appear after a
.Ql \e0
character are not searched.
Since the
.Fn strnstr
function is a
.Fx
specific API, it should only be used when portability is not a concern.
.Sh RETURN VALUES
If
.Fa little
is an empty string,
.Fa big
is returned;
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 EXAMPLES
The following sets the pointer
.Va ptr
to the
.Qq Li Bar Baz
portion of
.Va largestring :
.Bd -literal -offset indent
const char *largestring = "Foo Bar Baz";
const char *smallstring = "Bar";
char *ptr;

ptr = strstr(largestring, smallstring);
.Ed
.Pp
The following sets the pointer
.Va ptr
to
.Dv NULL ,
because only the first 4 characters of
.Va largestring
are searched:
.Bd -literal -offset indent
const char *largestring = "Foo Bar Baz";
const char *smallstring = "Bar";
char *ptr;

ptr = strnstr(largestring, smallstring, 4);
.Ed
.Sh SEE ALSO
.Xr memchr 3 ,
.Xr memmem 3 ,
.Xr strchr 3 ,
.Xr strcspn 3 ,
.Xr strpbrk 3 ,
.Xr strrchr 3 ,
.Xr strsep 3 ,
.Xr strspn 3 ,
.Xr strtok 3 ,
.Xr wcsstr 3
.Sh STANDARDS
The
.Fn strstr
function
conforms to
.St -isoC .
.Sh HISTORY
The
.Fn strnstr
function was introduced by
.Fx 4.5
and is non-standard.