public header class constructor

Question

I am new at building distributable libraries written in C++ and I am getting a bit lost. I have created a .cpp file with wrappers for all functions I want the library to offer users, and I have written 2 .h files, one public and one private. Below is a dummy example of my header files:

public.h:

class myclass
{
public:
    public_function();
private:
}

private.h:

class myclass
{
public:
    public_function();
private:
    anotherClass instanceofClass;
}

Note that the implementation of public_function() uses the "instanceofClass" in the code. I have been able to compile with no problem the code using the private class and to compile and link the library with external programs using the public header and the compiled library. When executing that code, though, I am getting segmentation faults that I suspect have to do with lack of proper initialization of "instanceofClass".

Am I doing the right thing? Am I forced to instantiate "instanceofClass" inside the implementation of public_function() for it to be initialized properly, or is there anything else I should do instead?

Thanks a lot.

Answer 1

You can't declare the same class 'myclass' in two different ways. There has to be a single class definition. If you want to hide the implementation's API you want to use the 'Pimpl' idiom. So your public class has a single pointer to a private class. For example:

public.h

class myclass_private;
class myclass {
    private:
        myclass_private* pimpl; 
    public:
        myclass();
        void public_function();
};

public.cpp

myclass::myclass() {
    pimpl = new myclass_private;
}

void myclass::public_function() {
     pimpl->private_function();
}

private.h

class myclass_private {
    public:
        void private_function(); 
};