derivative classes cause compiler to fail only if split between .h and .cpp file

[LJones]

I have a base class from which I'm trying to inherit members for various other classes. The only problem is that if I split up the derived class into a header and a cpp file, it won't compile. I've got the shortest example I can come up with.

//Base.h
class Base
{
    private:
        int pVar;
    protected:
        Base(int theVar) : pVar(theVar) {};
        int getBase() {return pVar;};
};

//Deriv.h
#include <iostream>
class Deriv : public Base
{
    public:
        Deriv() : Base(5) {};;
        ~Deriv();
        void test() {std::cout << getBaseVar();};
};

//main.cpp
#include <cstdlib>
#include <iostream>
#include "Base.h"
#include "Deriv.h"
int main(int argc, char *argv[])
{
    return 0;
}

The code above will compile. However, if I try to separate Deriv into 2 separate files as follow, the compile will fail:

//Deriv.h
class Deriv : public Base
{
    public:
        Deriv() : Base(5) {};
        ~Deriv();
        void test();
};

//Deriv.cpp
#include <iostream>
void Deriv::test()
{
    std::cout << getBaseVar();
}

the compiler will complain that Deriv has not been declared in the cpp file. I can solve this problem by adding #include "Deriv.h" at the top of Deriv.cpp, only to have the compiler complain about an expected class-name before '{' token on line 2 of Deriv.h. THIS I can fix by adding #include "Base.h" at the top of Deriv.h, at which point the compiler complains about class redefinition. At that point, I can compile and run the program by removing #include "Base.h" from main.cpp. However, as I have already included Base.h in Deriv.h at that point, I am unable to include it anywhere else to derive any more classes from it, as the compiler will complain about redefinition. Thus, the only way I can derive multiple classes from a given class is to contain all of my code in the derivative classes' header files.

[Disch]

Read this article: http://www.cplusplus.com/forum/articles/10627/


Basically:

1) You should include guard your headers
2) Deriv.h should be including Base.h
3) Deriv.cpp should be including Deriv.h

[LJones]

Light reading complete with cliffs notes. Thanks.