Question

I have a class called foo1 and in foo1.h I have

class foo1
{
public:
int var;
foo1();
};

There is also another class called foo2, in which I have an object based on foo1:

class foo2
{
public:
foo1 *afoo1;
foo2();
void func1(int,int);
};

My question is that how I can have access to afoo1->var. If I use afoo1->var in foo2.cpp, everything looks fine and it compiles with no error. But when I run it in the command prompt window, a window pups up and asks to close the program. I guess this is because I am violating memory access, the cause of which could be afoo1->var.

Can anyone help me with this?

Thanks

Extra Note

I make a dll file from foo2, and use it in another program, the source code of which I do not have any access to. Just to make things clarified a bit more.

Answer

I had made two mistakes. The first one was that I was referencing to Null. afoo1 = new foo1(); in the constructor of foo2 took care of that.

The second one was that I had not included foo1.cpp in my makefile. I know, stupid mistake.

Answer 1

You need to do foo2Instance->afoo1->var, inside the foo2 methods this will just be afoo1->var. If that is crashing it’s more likely because you’re not initializing afoo1 in foo2’s constructor.

#ifndef FOO1_H
#define FOO1_H 

class foo1
{
public:
int var;
foo1() { var = 0; } //make sure the constructor is in fact defined. 
// if it isn't implemented it would cause that linker error.
};

#endif

Make sure you have #include "foo1.h" in foo2.h

   // constructor and deconstructor, these are in the cpp file.
   foo2::foo2()
   {
        afoo1 = new foo1();
   }
   foo2::~foo2()
   {
        delete afoo1;
   }

If you’re getting a NullReferenceException it’s likely because you’re missing that line in the constructor. afoo2->afoo1 is fine when afoo1 == NULL however, if you try to access a property of afoo1 you will crash every time. NULL->someProperty is never okay.