Thread: error with 2 header files calling each other

i get error when i compile..
here is my code

Code:

/*this is my header file for my file called C.h*/
#ifndef _C_H_
#define _C_H_
#include "I.h"
using namespace std;
class C {
 public:
    void get_foo(int, int);
    void set_bar(int,I*);
    void monkey(int, I*);
    void cow(I*);
 private:
    I * stinky; 
};
#endif

Code:

/*This is my header file for my file called I.h*/
#ifndef _I_H_
#define _I_H_
#include "C.h"
using namespace std;
class I{
 public:
      void get_monkey(int, C *);
 private:
      C * hello;
};
#endif

Now when i compile my program i get errors relating to all the lines that contain the type of other header file.
so in the I.h i get errors on all the lines that have the type C.
and in the C.h i get errors on all the lines that have the type I.

Code:

In file included from I.h:3,
                 from I.cpp:2:
C.h:31: error: type specifier omitted for parameter `Item'
C.h:31: error: syntax error before `*' token
C.h:33: error: type specifier omitted for parameter `Item'
C.h:33: error: syntax error before `*' token
C.h:34: error: `Item' was not declared in this scope
C.h:34: error: syntax error before `)' token
C.h:49: error: syntax error before `*' token
make: *** [I.o] Error 1

/*ignore the line numbers because i have removed all the irrelevant functions for this example*/
but here line 31 is referring to
   void set_bar(int,I*);
from the C.h file.

Elad, that is a forward declaration, and it is the correct way to go about things. You can forward declare I in C.h and then include C.h in I.h, or simply forward declare I and C in the right files.

Don't forget to include I.h in C.c and C.h in I.c! If you don't, it won't work because the compiler still needs to know how the whole class is laid out.

And I think forward declarations won't work for templates because the implementation is in the header file (thus the compiler needs to know where the fields and methods are). Could be wrong on this one...haven't written a template class in awhile.

PK

thanks