freebsd-dev/lib/libc/string/strstr.3

.\" Copyright (c) 2001 Mike Barcroft <mike@FreeBSD.org>
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.\"     @(#)strstr.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD$
.\"
.Dd June 4, 1993
.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"
.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 strnstr
function
locates the first occurrence of the null-terminated string
.Fa little
in the string
.Fa big ,
where only the first number of characters, identified by
.Fa len ,
are searched.
Since the
.Fn strnstr
function is a
.Fx
specific API, it should only be used when portablility 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 ,
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
.Dq 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 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 strchr 3 ,
.Xr strcspn 3 ,
.Xr strpbrk 3 ,
.Xr strrchr 3 ,
.Xr strsep 3 ,
.Xr strspn 3 ,
.Xr strtok 3
.Sh STANDARDS
The
.Fn strstr
function
conforms to
.St -isoC .