Question

I more or less have an idea, but I’m not sure if I’ve even got the right idea and I was hoping maybe I was just missing something obvious. Basically, I have and array of strings (C strings, so basically an array of pointers to character arrays) like so:

char **words;

Which I don’t know how many words I’ll have in the end. As I parse the string, I want to be able to resize the array, add a pointer to the word, and move on to the next word then repeat.

The only way I can think of is to maybe start with a reasonable number and realloc every time I hit the end of the array, but I’m not entirely sure that works. Like I want to be able to access words[0], words[1], etc. If I had char **words[10] and called

realloc(words, n+4)  //assuming this is correct since pointers are 4 bytes

once I hit the end of the array, if I did words[11] = new word, is that even valid?

Answer 1

Keep track of your array size:

size_t arr_size = 10;

And give it an initial chunk of memory:

char **words = malloc( arr_size * sizeof(char*) );

Once you have filled all positions, you may want to double the array size:

size_t tailIdx = 0;

while( ... ) {
    if( tailIdx >= arr_size ) {
        char **newWords;
        arr_size *= 2;
        newWords = realloc(words, arr_size * sizeof(char*) );
        if( newWords == NULL ) { some_error() };
        words = newWords;
    }
    words[tailIdx++] = get_next_word();
}

...

free(words);