Box2D Collision Issues - c++

Question

Very new at Box2D, would appreciate help.
I've got a simple function that takes in a b2World and b2Body*, where the body is supposed to fall until it collides with a ground box (already created in main())
The code is essentially as follows:
void snake::update(b2World world, b2Body* snake)
{
bool running = true;
Clock deltaClock;
Time deltaTime;
while (running)
{
deltaTime = deltaClock.getElapsedTime();
deltaClock.restart();
world.Step(deltaTime.asSeconds(), 6, 2);
position = snake->GetPosition();
char ch;
if (_kbhit())
{
ch = _getch();
if (ch == 'x')
{
running = false;
}
}
}
}
This code was originally implemented in main(), and it worked fine. However, when I tried to move it to its own function in a separate class, the collision no longer works... I've got no idea as to why, as it was literally copy/pasted, just changing around variable names to fit the parameters...
I've got no idea what's going wrong, and if you need any additional information, I'd be more than happy to provide.
Thanks in advance.

Answer 1

Basically the way you had your parameter set before you were passing the b2World object by value in your original function head.
void snake::update(b2World world, b2Body* snake)
This means you are creating a copy and if this copy is being modified, the original object that was passed to the function remains the same. With the & behind the type you are now passing the object by reference.
void snake::update(b2World& world, b2Body* snake)
This means there is no copy being created but instead the function works with the original object and thus, changes do affect it aswell.
So when you were using this loop before it was probably nested inside of your main function or whatever and could modify the original variable world which was declared in that scope. Now that you have moved it to a seperate function you have to tell the compiler you want to work with the original object.
Read more about passing by value and passing by reference here and here for example