C++ won't let me make friends

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 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 m…

Accepted Answer

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
```

C++ won't let me make friends

Solution

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