Question

I have one class, called A, and it has it’s own header file. Then I have another class, called B, which also has it’s own header file. They each have their own .cpp file where I implement all of their functions.

I’m trying to have class B have a variable of class type A as a private variable, but I keep getting the error ‘A’ does not name a type

My code looks like this:

main.h:

#ifndef MAIN_H
#define MAIN_H

#include "A.h"
#include "B.h"

#endif

main.cpp:

#include "main.h"

int main( int argc, char* args[]) {
  B test;
}

A.h:

#ifndef A_H
#define A_H

#include "main.h"

class A {
  public:
    //public functions
  private:
    //private variables
};
#endif

B.h:

#ifndef B_H
#define B_H

#include "main.h"

class B {
  public:
    //public functions...
  private:
    A temp;
}
#endif

So all of my includes are in main.h, which includes A before B. B has a variable of type A, but it is included from being in main.h and B.h includes main.h. However, I keep getting an error saying:

error: 'A' does not name a type.

I’ve done some googling, and it seems like that means that A isn’t defined when you use it, but it should be defined there since it’s being included in main.h, right?

Answer 1

The problem is that A.h includes main.h, which includes B.h, which tries to use A.

The good way to organize your files would be this:

main.h:

// not needed

main.cpp:

#include "B.h" // for using class B

int main( int argc, char* args[]) {
  B test;
}

A.h:

#ifndef A_H
#define A_H

// no includes needed ATM

class A {
  //...
};
#endif

B.h:

#ifndef B_H
#define B_H

#include "A.h" // for using class A

class B {
  //public functions...
}
#endif

That way, B.h is self-contained and can be used without having to include anything else before it. That’s very important as soon as your project grows above the toy level it is at now. Why would anyone trying to use what header x.h provides need to know to also include f.h, m.h, and u.h?