Question

Suppose I write my code very defensively and always check the return types from all the functions that I call.

So I go like:

char* function() {
    char* mem = get_memory(100);  // first allocation
    if (!mem) return NULL;

    struct binder* b = get_binder('regular binder');  // second allocation
    if (!b) {
        free(mem);
        return NULL;
    }

    struct file* f = mk_file();  // third allocation
    if (!f) {
        free(mem);
        free_binder(b);
        return NULL;
    }

    // ...
}

Notice how quickly free() things get out of control. If some of the function fails, I have to free every single allocation before. The code quickly becomes ugly and all I do is copy paste everything over. I become a copy/paste programmer, even worse, if someone adds a statement somewhere in between, he has to modify all the code below to call the free() for his addition.

How do experienced C programmers go about this problem? I can’t figure anything out.

Thanks, Boda Cydo.

Answer 1

You could define a new label that would free the resources and then you could GOTO it whenever your code fails.

char* function()
{
    char* retval = NULL;
    char* mem = get_memory(100);  // first allocation
    if (!mem)
        goto out_error;

    struct binder* b = get_binder('regular binder');  // second allocation
    if (!b)
        goto out_error_mem;

    struct file* f = mk_file();  // third allocation
    if (!f)
        goto out_error_b;

    /* ... Normal code path ... */
    retval = good_value;

  out_error_b:
    free_binder(b);
  out_error_mem:
    free(mem);
  out_error:
    return retval;
}

Error management with GOTO was already discussed here:
Valid use of goto for error management in C?