Question

Can someone please give me an example of how public and private headers work? I have done some reading on the net but I can’t seem to find much useful information with sample codes. I was advised that I should use private headers to separate the public and private parts of my code for creating a static library. After some reading I have a general idea of how it works, but would really appreciate a good example to get me started. Specifically, what I don’t quite understand is how to put the interface functions in my public header, and the private variables/functions in my private header? Thanks!

EDIT:

Maybe I’m not wording my question right, but what I meant is, for example, I have myMath.h and myMath.cpp, and myMath.h has:

class myMath{
public:
    void initialise(double _a, double _b);
    double add();
    double subtract();

private:
    double a;
    double b;
};

And myMath.cpp has the implementations of the functions. How can I make it so that myMath.h only has the three public functions, and the private variables are defined in another file (e.g. myMath_i.h), and these three files are in such a way that after I create a static library, only myMath.h is needed by users. This also means myMath.h cannot #include myMath_i.h. So something like:

myMath.h:

class myMath{
public:
    void initialise(double _a, double _b);
    double add();
    double subtract();
}

and myMath_i.h:

class myMath{
private:
    double a;
    double b;
}

Of course that’s not possible because then I’ll be redefining the class myMath…

Answer 1

You have two header files MyClass.h and MyClass_p.h and one source file: MyClass.cpp.

Lets take a look at what’s inside them:

MyClass_p.h:

// Header Guard Here
class MyClassPrivate
{
public:
    int a;
    bool b;
    //more data members;
}

MyClass.h:

// Header Guard Here
class MyClassPrivate;
class MyClass
{
public:
    MyClass();
    ~MyClass();
    void method1();
    int method2();
private:
    MyClassPrivate* mData;
}

MyClass.cpp:

#include "MyClass.h"
#include "MyClass_p.h"

MyClass::MyClass()
{
    mData = new MyClassPrivate();
}

MyClass::~MyClass()
{
    delete mData;
}

void MyClass::method1()
{
    //do stuff
}

int MyClass::method2()
{
    return stuff;
}

Keep your data in MyClassPrivate and distribute MyClass.h.