C++

Forum

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

LJones (7)
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.

1
2
3
4
5
6
7
8
9
 
//Base.h
class Base
{
    private:
        int pVar;
    protected:
        Base(int theVar) : pVar(theVar) {};
        int getBase() {return pVar;};
};

1
2
3
4
5
6
7
8
9
 
//Deriv.h
#include <iostream>
class Deriv : public Base
{
    public:
        Deriv() : Base(5) {};;
        ~Deriv();
        void test() {std::cout << getBaseVar();};
};

1
2
3
4
5
6
7
8
9
 
//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:

1
2
3
4
5
6
7
8
 
//Deriv.h
class Deriv : public Base
{
    public:
        Deriv() : Base(5) {};
        ~Deriv();
        void test();
};

1
2
3
4
5
6
 
//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.
Last edited on
Disch (13742)
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 (7)
Light reading complete with cliffs notes. Thanks.
Topic archived. No new replies allowed.