Using class object in another class

[kingkush]

Im getting an error: use of undeclared identifier. I created an class with its own .h and .cpp. We'll call this ClassA and created a second class
with in its own files, we'll call this ClassB, that uses ClassA objects.

Class ClassB
{
public:
   vector<ClassA> errorHere      

Would i need to use inheritance?

[gunnerfunner]

Would i need to use inheritance?

you'd use inheritance when there is a relationship b/w the classes e.g. is-a relationships can be modelled with public inheritance, has-a relationships with private or protected nheritance etc. there are also other ways of usings object of one class in another – search containment / composition / layering in C++
a good reference is: C++ Primer Plus (5th edition) – Stephen Prata – Chapter 14 – section: Classes with Object Members
as for the little code snippet that you posted, class B needs to see the complete definition (not just declaration) of class A as you're using objects of (not pointers to) type A in B:

#include <iostream>
#include <vector>

class A{};//definition of class A
//class A; //declaration of class A - will produce incomplete type error message

class B{public: std::vector<A> m_VecOfA;};

int main()
{
    B b;
    std::cout << b.m_VecOfA.size() << "\n";//prints 0
}

[kingkush]

I was able to get it to work but I don't think its recognizing CardTemplate because the function is no longer working. Would forward declaration be a possible solution?

[JLBorges]

> Would i need to use inheritance?

No. You would need to #include "ClassA.h" before defining classB.

[kingkush]

I was under the impression including another class.h file in another was bad practice?

[JLBorges]

Including one header in another header gratuitously is bad practice.

There are many situations where one header needs to include another header; the general rule is: if you do not need it, do not include it. For instance, in many cases, it may be sufficient if we include the header in the implementation (.cpp) file.