Question

I have two classes, Mesh and MeshList. I want MeshList to have a function that can change the private members of Mesh. But it won’t compile and I don’t know why. Here’s my code.

Mesh.h

#ifndef _MESH_H
#define _MESH_H

#include "MeshList.h"
#include <iostream>

class Mesh
{
private:
    unsigned int vboHandle_;
    friend void MeshList::UpdateVBOHandle();
public:
    inline void Out() {std::cout << vboHandle_;}
};
#endif

Mesh.cpp

#include "Mesh.h"

MeshList.h

#ifndef _MESH_LIST_H
#define _MESH_LIST_H

#include "Mesh.h"


class MeshList
{

public:
    Mesh *mesh; //Line 11 Error
    void UpdateVBOHandle();
};
#endif

MeshList.cpp

#include "MeshList.h"

void MeshList::UpdateVBOHandle()
{
    *mesh->vboHandle_ = 4;
}

I get these errors:

MeshList.h (Line 11)

• error C2143: syntax error : missing ‘;’ before ‘*’
• error C4430: missing type specifier – int assumed. Note: C++ does not
  support default-int

• error C4430: missing type specifier – int assumed. Note: C++ does not
  support default-int

• mesh.h(11) : error C2653: ‘MeshList’ : is not a class or namespace
  name

• meshlist.cpp(5) : error C2248: ‘Mesh::vboHandle_’ : cannot access
  private member declared in class ‘Mesh’
• mesh.h(10) : see declaration of ‘Mesh::vboHandle_’
• mesh.h(8) : see declaration of ‘Mesh’
• meshlist.cpp(5) : error C2100: illegal indirection

Answer 1

Cyclic dependencies are explained in the other answers…

Here comes the solution:

In MeshList.h:

• replace #include "Mesh.h" with the forward declaration class Mesh; (You don’t need the include here, because you only declare a pointer to a Mesh)

In MeshList.cpp:

• add #include "Mesh.h" to your includes (you need the declaration, because you use the Mesh)

The last compile error, you mentioned is another problem:

*mesh->vboHandle_ = 4;

mesh is a pointer. Your code selects the member vboHandle_ and tries to dereference it (which fails). I suppose you mean:

mesh->vboHandle_ = 4; // <-- no leading asterisk