NAME
strtok, strtok_r —
string tokens
LIBRARY
library “libc”
SYNOPSIS
#include
<string.h>
char *
strtok(char
* restrict str, const
char * restrict sep);
char *
strtok_r(char
*str, const char
*sep, char
**lasts);
DESCRIPTION
Thestrtok()
function is used to isolate sequential tokens in a nul-terminated string,
str. These tokens are separated in the string by at
least one of the characters in sep. The first time that
strtok() is called, str should
be specified; subsequent calls, wishing to obtain further tokens from the same
string, should pass a null pointer instead. The separator string,
sep, must be supplied each time, and may change between
calls.
The
strtok()
function returns a pointer to the beginning of each subsequent token in the
string, after replacing the separator character itself with a
NUL character. Separator characters at the beginning
of the string or at the continuation point are skipped so that zero length
tokens are not returned. When no more tokens remain, a null pointer is
returned.
The
strtok_r()
function implements the functionality of strtok()
but is passed an additional argument, lasts, which
points to a user-provided pointer which is used by
strtok_r() to store state which needs to be kept
between calls to scan the same string; unlike
strtok(), it is not necessary to limit tokenizing to
a single string at a time when using strtok_r().
EXAMPLES
The following will construct an array of pointers to each individual word in the string s:
#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)), i++) {
if (i < MAXTOKENS - 1)
tokens[i] = p;
}
tokens[i] = NULL;
That is, tokens[0] will point to
"cat", tokens[1] will point to
"dog", tokens[2] will point to
"horse", and tokens[3] will point to
"cow".
SEE ALSO
index(3), memchr(3), rindex(3), strchr(3), strcspn(3), strpbrk(3), strrchr(3), strsep(3), strspn(3), strstr(3)
STANDARDS
The strtok() function conforms to
ANSI X3.159-1989 (“ANSI C89”).
The strtok_r() function conforms to
IEEE Std 1003.1c-1995
(“POSIX.1c”).
BUGS
The System V strtok(), if handed a string
containing only delimiter characters, will not alter the next starting
point, so that a call to 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 NULL.