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.\"	$OpenBSD: strtok.3,v 1.19 2007/05/31 19:19:32 jmc Exp $
.\"
.Dd $Mdocdate: May 31 2007 $
.Dt STRTOK 3
.Os
.Sh NAME
.Nm strtok ,
.Nm strtok_r
.Nd string token operations
.Sh SYNOPSIS
.Fd #include <string.h>
.Ft char *
.Fn strtok "char *str" "const char *sep"
.Ft char *
.Fn strtok_r "char *str" "const char *sep" "char **last"
.Sh DESCRIPTION
.Bf -symbolic
This interface is obsoleted by
.Xr strsep 3 .
.Ef
.Pp
The
.Fn strtok
function is used to isolate sequential tokens in a NUL-terminated string,
.Fa str .
These tokens are separated in the string by at least one of the
characters in
.Fa sep .
The first time that
.Fn strtok
is called,
.Fa str
should be specified; subsequent calls, wishing to obtain further tokens
from the same string, should pass a null pointer instead.
The separator string,
.Fa sep ,
must be supplied each time, and may change between calls.
.Pp
The
.Fn strtok_r
function is a version of
.Fn strtok
that takes an explicit context argument and is reentrant.
.Pp
The
.Fn strtok
and
.Fn strtok_r
functions return a pointer to the beginning of each subsequent token
in the string, after replacing the separator character itself with an
.Tn ASCII NUL
character.
When no more tokens remain, a null pointer is returned.
.Pp
Since
.Fn strtok
and
.Fn strtok_r
modify the string,
.Fa str
should not point to an area in the initialized data segment.
.Sh EXAMPLES
The following will construct an array of pointers to each individual word in
the string
.Va s :
.Bd -literal -offset indent
#define MAXTOKENS	128

char s[512], *p, *tokens[MAXTOKENS];
char *last;
int i = 0;

snprintf(s, sizeof(s), "cat dog horse cow");

for ((p = strtok_r(s, " ", &last)); p;
    (p = strtok_r(NULL, " ", &last))) {
	if (i < MAXTOKENS - 1)
		tokens[i++] = p;
}
tokens[i] = NULL;
.Ed
.Pp
That is,
.Li tokens[0]
will point to
.Qq cat ,
.Li tokens[1]
will point to
.Qq dog ,
.Li tokens[2]
will point to
.Qq horse ,
and
.Li tokens[3]
will point to
.Qq cow .
.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 strstr 3
.Sh STANDARDS
The
.Fn strtok
function conforms to
.St -ansiC .
.Sh BUGS
The System V
.Fn strtok ,
if handed a string containing only delimiter characters,
will not alter the next starting point, so that a call to
.Fn strtok
with a different (or empty) delimiter string
may return a non-null value.
Since this implementation always alters the next starting point,
such a sequence of calls would always return
.Dv NULL .