STRTOK(3) FreeBSD Library Functions Manual STRTOK(3)


strtok, strtok_rstring 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 = strtok_r(NULL, sep, &brkt)) 
    strcpy(blah, "blah:blat:blab:blag"); 
    for (phrase = strtok_r(blah, sep, &brkb); 
         phrase = strtok_r(NULL, sep, &brkb)) 
        printf("So far we're at %s:%s\n", word, phrase); 


The strtok() function conforms to ISO/IEC 9899:1990 (“ISO C90”).


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

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.
November 27, 1998 FreeBSD