get the classes under the specified class.

[Saile]

Hello. I'm working with classes at the moment. What i wanna do is to get/handle the class B from class A. I red that you can write the name of the class above both classes in this case, as you can do with functions, but the linker writes: "has initializer but incomplete type". I wonder of you can do something similar with vectors aswell.

class B;
 
class A
{
void get();
};
 
void A::get()
{
B b_class;
b_class.test();
}
 
class B
{
void test();
};
 
void B::test()
{
cout << "test" << endl;
}
 

[weaknessforcats]

class B; <<<<Forward reference

class A
{
void get();
};

void A::get()
{
B b_class; <<<<< Error
b_class.test();
}

class B
{
void test();
};

void B::test()
{
cout << "test" << endl;
}

I made a couple of marks in your code above. First, a class reference is an instruction to the compiler that a class exists even though the compiler has not yet seen the class declaration. Here it says B is a class.

So far, so good.

However in A::get(), there is an object b_class with a type of B. For the compiler to accept this, there must be a class B (there is according to the forward reference) and that class B must have a default constructor (which you can't tell from the forward reference). So you get a compile error.

You say you get a linker error. I doubt that. It's a compile error.

The forward reference is good enough for the compiler to allow a B* but not good enough for the compiler to allow a B object. When you need a B object, then you have to put the class B declaration before the class A declaration.

[Saile]

You mentioned "forward reference", so I searched for it on google and found out this way to solve it:

class B;
 
class A
{
public:
B *b;
void get();.
};
 
class B
{
void test();
};
 
void B::test()
{
cout << "test" << endl;
}
 
void A::get()
{
b = new B;
b->test();
}
 

And yes I misswrote, I ment compiler error. :)

[weaknessforcats]

Yep. That's the way.