2008/3/19 Wesley Smith <wesley.hoke@xxxxxxxxx>:
> Vec3 *v = vectors;
> for(int i=0; i < 100; i++) {
> Vec3 v_rand;
> v_rand.random(); //make a random vector;
>
> *v++ += v_rand;
> }
>
>
> /////example 2
>
> Vec3 *v = vectors;
> Vec3 v_rand;
> for(int i=0; i < 100; i++) {
> v_rand.random(); //make a random vector;
>
> *v++ += v_rand;
> }
>
>
> Clearly there are scope differences between the 2 examples, but in
> terms of performance, how do compilers handle these situations.
The first version needs to have a ctor and dtor call invoked on every
iteration of the loop. Depending on what they do that will slow the
code down. If you insert a printf() call in Vec3's constructor and
destructor you'll see the difference. With GCC 4+ you can also use
-fdump-tree-gimple to get a C-like representation of your program.
Diego.
