Question

I’m a little confused about how C++ handles includes.

I have something like:

typedef struct {
  //struct fields
} Vertex;

#include "GenericObject.h"

Now in GenericObject.h I have:

class GenericObject {
  public:
    Vertex* vertices; 
}

When I try to compile, the compiler says:

ISO C++ forbids declaration of ‘Vertex’ with no type

How do I get GenericObject.h to know about Vertex?

I was under the impression that anything defined before an #include, was available in the included files.

And lastly, could you give me some tips on how to correctly use #include without introducing too much redundancy or circular includes.

Thanks.

Answer 1

Two things, first you want it to just be…

struct Vertex
{
//struct fields
};

That is a properly defined struct in C++.
Now you either need to include Vertex.h, or what ever file contains the vertex struct, in your generic object header,

#include "Vertex.h"
class GenericObject {
public:
   Vertex* vertices; 
};

or forward declare it as so…

struct Vertex;
class GenericObject {
  public:
    Vertex* vertices; 
};

don’t #include “GenericObject.h” from “Vertex.h”.