Question

I’m not very familiar with C++ programming. I know the basics of programming in it (syntax, pointers, etc.) and I’ve built a few basic programs with it and done some basic debugging at work. I am puzzled by this line of code from Box2D, specifically the Box2dTest project from Cocos2D:

// Define the ground body.
b2BodyDef groundBodyDef;
groundBodyDef.position.Set(0, 0); // bottom-left corner

How is it that one can do this without having initialized groundBodyDef? I know this isn’t an Objective-C thing because the C++ examples for Box2D itself are just like this.

Answer 1

groundBodyDef actually is initialized!

I think you expected something along the lines of:

b2BodyDef *groundBodyDef = new b2BodyDef();

which is actually still valid, but it is initialized on the heap. In your version, groundBodyDef is initialized on the stack, much like you would initialize an int on the stack.

As it is called without parameters, the default constructor is used.