Accessing private members in a class

Question

I need to access an object from a DLL, do some manipulations to the object and feed the object to another function. The trouble is the fields I need to change are private.

I don't want to change the private modifier for the fields in the original class because the class was written a long time ago and is used in many places. However, the place where I am manipulating the class I need most of the fields without protection (it is a hack). What is the best way to do it?

Note: I am not allowed to change the original class

Answer 1

If you can see the original class you can make a mock class with the same bit pattern and cast the original object to the mock class object

Example below

Original class

class ClassWithHiddenVariables
{
private:
    int a;
    double m;

}; 

Mock class

 class ExposeAnotherClass
    {
    public:
        int a_exposed;
        double m_exposed;
    };

When you want to see members of the ClassWithHiddenVariables object, use reinterpret_cast to cast to ExposeAnotherClass

 ClassWithHiddenVariables obj;
    obj.SetVariables(10, 20.02);    
    ExposeAnotherClass *ptrExposedClass;
    ptrExposedClass = reinterpret_cast<ExposeAnotherClass*>(&obj);  
    cout<<ptrExposedClass->a_exposed<<"\n"<<ptrExposedClass->m_exposed;