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String tokens
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#include <string.h>
char strtok (char *str, const char *sep)
char strtok_r (char *str, const char *sep, char **last)


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.

Example - String tokens
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").


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.