Question

Guys, I am very new to c++. I have just wrote this class:

class planet
{
public:
 float angularSpeed;
 float angle;
};

Here is a function trying to modify the angle of the object:

void foo(planet* p) 
{
  p->angle = p->angle + p->angularSpeed;
}

planet* bar = new planet();
bar->angularSpeed = 1;
bar->angle = 2;
foo(bar);

It seem that the angle in bar didn’t change at all.

Answer 1

Note that you are passing bar by pointer, not by reference. Pass-by-reference would look like this:

void foo(planet& p)  // note: & instead of *
{
    p.angle += p.angularSpeed;   // note: . instead of ->
}

Pass-by-reference has the added benefit that p cannot be a null reference. Therefore, your function can no longer cause any null dereferencing error.

Second, and that’s a detail, if your planet contains only public member variables, you could just as well declare it struct (where the default accessibility is public).

PS: As far as I can see it, your code should work; at least the parts you showed us.