Question

Given a C-string: how would I be able to write a function that will get the next token in the string, and a function that will peek the next token and return that without using global variables?

What I’m trying to do is have a static variable that will hold the string, and when called, it would just increment a pointer, and it will reset that static variable throwing out the token that has been retrieved. The problem is: how would I be able to differentiate between the first call (when it will actually store the string) and the other calls, when I am just retrieving it?

Any thoughts on this?

EDIT:
Here’s what I have now that “works” but I want to make sure that it should actually work and its not just a coincidence of a pointer being null:

char next_token(char *line) {
    static char *p;
    if (p == NULL)
        p = line;
    else {
        char next_token = p[0];
        p++;
        return next_token;
    }
}

Answer 1

The code in your edit is wrong. You are handling the NULL case incorrectly.

I initially answered in terms of emulating strtok which seemed to be what you wanted, but you have clarified that you want single characters.

The if-condition should be:

if (line != NULL) p = line;

And you presumably remove the else so that code executes every time… Unless you don’t want a result on the first call (you should at least return a value though).

You call like this:

char token = next_token(line);

while( 0 != (token = next_token(NULL)) ) {
    // etc
}