What is the recommended way to use defer to free values only on an error path (rather than all paths)? Currently I use goto for this:

    void* p1 = malloc(...);
    if (!p1) goto err1;
    void* p2 = malloc(...);
    if (!p2) goto err2;
    void* p3 = malloc(...);
    if (!p3) goto err3;

    return {p1, p2, p3};

    err3: free(p2);
    err2: free(p1);
    err1: return NULL;

With defer I think I would have to use a "success" boolean like this:

    bool success = false;

    void* p1 = malloc(...);
    if (!p1) return NULL;
    defer { if (!success) free(p1) }

    void* p2 = malloc(...);
    if (!p2) return NULL;
    defer { if (!success) free(p2) }

    void* p3 = malloc(...);
    if (!p3) return NULL;
    defer { if (!success) free(p3) }

    success = true;
    return {p1, p2, p3};

I'm not sure if this has really improved things. I do see the use-case for locks and functions that allocate/free together though.