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Manual Pages  — STRTOK


strtok – string tokens



Standard C Library (libc, -lc)


#include <string.h>

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

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


This interface is obsoleted by strsep(3).

The strtok() function is used to isolate sequential tokens in a null-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 implementation will behave as if no library function calls strtok().

The strtok_r() function is a reentrant version of strtok(). The context pointer last must be provided on each call. The strtok_r() function may also be used to nest two parsing loops within one another, as long as separate context pointers are used.

The strtok() and strtok_r() functions return a pointer to the beginning of each subsequent token in the string, after replacing the token itself with a NUL character. When no more tokens remain, a null pointer is returned.


The following uses strtok_r() to parse two strings using separate contexts:
char test[80], blah[80];
char *sep = "\\/:;=-";
char *word, *phrase, *brkt, *brkb;

strcpy(test, "This;is.a:test:of=the/string\\tokenizer-function.");

for (word = strtok_r(test, sep, &brkt); word; word = strtok_r(NULL, sep, &brkt)) { strcpy(blah, "blah:blat:blab:blag");

for (phrase = strtok_r(blah, sep, &brkb); phrase; phrase = strtok_r(NULL, sep, &brkb)) { printf("So far we're at %s:%s\n", word, phrase); } }


memchr(3), strchr(3), strcspn(3), strpbrk(3), strrchr(3), strsep(3), strspn(3), strstr(3), wcstok(3)


The strtok() function conforms to ISO/IEC 9899:1990 ("ISO C90"). The strtok_r() function conforms to IEEE Std 1003.1-2001 ("POSIX.1").


Wes Peters <Mt wes@softweyr.com>, Softweyr LLC

Based on the FreeBSD 3.0 implementation.


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.

STRTOK (3) January 22, 2016

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