tokenizing a string twice in c with strtok()

Question

I'm using strtok() in c to parse a csv string. First I tokenize it to just find out how many tokens there are so I can allocate a string of the correct size. Then I go through using the same variable I used last time for tokenization. Every time I do it a second time though it strtok(NULL, ",") returns NULL even though there are still more tokens to parse. Can somebody tell me what I'm doing wrong?

char* tok;
int count = 0;
tok = strtok(buffer, ",");
while(tok != NULL) {
    count++;
    tok = strtok(NULL, ",");
}

//allocate array

tok = strtok(buffer, ",");
while(tok != NULL) {
    //do other stuff
    tok = strtok(NULL, ",");
}

So on that second while loop it always ends after the first token is found even though there are more tokens. Does anybody know what I'm doing wrong?

Answer 1

strtok() modifies the string it operates on, replacing delimiter characters with nulls. So if you want to use it more than once, you'll have to make a copy.