Question

I’m relatively new to C++. I was looking into the source code of Box2D to learn how professional people manage their code and found this kind of pairs quite a lot:

inline b2Body* b2World::GetBodyList()
{
    return m_bodyList;
}

inline const b2Body* b2World::GetBodyList() const
{
    return m_bodyList;
}

Questions that popped into my mind is, how do we know which function that we called? What’s the reasoning for this kind of pair?

Answer 1

The non-const version cannot be called on a const b2World; note that the return types of the methods are different. Try running

#include <iostream>

struct Foo
{
    void greet() { std::cout << "Hello, world!\n"; }
    void greet() const { std::cout << "Hello, const world!\n"; }
};

int main()
{
    Foo foo;
    foo.greet();

    Foo const &fooref(foo);
    fooref.greet();
}

See also the C++ FAQ Lite on const-correctness.