14.8. strtok()

Tokenize a string.


#include <string.h>
char *strtok(char *str, const char *delim);


If you have a string that has a bunch of separators in it, and you want to break that string up into individual pieces, this function can do it for you.

The usage is a little bit weird, but at least whenever you see the function in the wild, it's consistently weird.

Basically, the first time you call it, you pass the string, str that you want to break up in as the first argument. For each subsequent call to get more tokens out of the string, you pass NULL. This is a little weird, but strtok() remembers the string you originally passed in, and continues to strip tokens off for you.

Note that it does this by actually putting a NUL terminator after the token, and then returning a pointer to the start of the token. So the original string you pass in is destroyed, as it were. If you need to preserve the string, be sure to pass a copy of it to strtok() so the original isn't destroyed.

Return Value

A pointer to the next token. If you're out of tokens, NULL is returned.


// break up the string into a series of space or
// punctuation-separated words
char *str = "Where is my bacon, dude?";
char *token;

// Note that the following if-do-while construct is very very
// very very very common to see when using strtok().

// grab the first token (making sure there is a first token!)
if ((token = strtok(str, ".,?! ")) != NULL) {
    do {
        printf("Word: \"%s\"\n", token);

        // now, the while continuation condition grabs the
        // next token (by passing NULL as the first param)
        // and continues if the token's not NULL:
    } while ((token = strtok(NULL, ".,?! ")) != NULL);

// output is:
// Word: "Where"
// Word: "is"
// Word: "my"
// Word: "bacon"
// Word: "dude"

See Also

strchr(), strrchr(), strspn(), strcspn()