asprintf - when to use free()?

asprintf says

The functions asprintf() and vasprintf() are analogs of sprintf(3) and vsprintf(3), except that they allocate a string large enough to hold the output including the terminating null byte, and return a pointer to it via the first argument. This pointer should be passed to free(3) to release the allocated storage when it is no longer needed.

Here is my C code

void function(){
    char *out = NULL;
    int parts[16] = {1,2,05,003};
    asprintf(&out, "%d.%d.%d.%d", parts[0], parts[1], parts[2], parts[3]);
  //  free(out);
}

int main(void){
    function();
    return 0;
}

When the function is monitored on the debug mode, I see that the variable is already destroyed when it returns from the function. Why I don't need to free() the code above?

Could you tell me in what cases of asprintf I need to use free?

btw, I have "gcc version 4.7.2 (Ubuntu/Linaro 4.7.2-2ubuntu1)"

You need to call free().

The variable leaves the scope, so the actual value of the variable (the address that free() needs) is lost at that point, creating a memory leak.

The free() function is interested in the address of memory previously returned by malloc() or some other heap allocation call, not at all in your particular variable.

You could do:

char *out = NULL, *a, *b, *c, *d, *e;
int parts[16] = {1,2,05,003};
asprintf(&out, "%d.%d.%d.%d", parts[0], parts[1], parts[2], parts[3]);
a = b = c = d = e = out;

and that's just five more variables holding copies of the same address going out of scope. The heap subsystem (as reached through the malloc()/free() calls) knows nothing about this, of course.