NAME

strtok, strtok_r — string tokens

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <string.h>

char *
strtok(char * restrict str, const char * restrict sep);

char *
strtok_r(char *str, const char *sep, char **lasts);

DESCRIPTION

The strtok() 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.1”).

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.