A header file do not recognize another

cpit · #1 21-Mar-2008, 14:39

Hi all,

I'm trying to create a method that receive an object as an argument. I get it working when the two classes are defined in the same file.h. However, I would like to know how to do that with two files.h.

For instance, this is my code that works,

CPP / C++ / C Code:

//file classes.h

class Cvalues{
		
	public:
	int x,y;
	void set_values(int,int);
	void get_values();	
};

class Ccalc{
	int x,y;
	
	public:
	int sum(int, int);
	int sum(Cvalues&);
};

Now, I would like to write a class in each file (classes1.h, classes2.h)

CPP / C++ / C Code:

//file classes1.h

class Cvalues{
		
	public:
	int x,y;
	void set_values(int,int);
	void get_values();	
};

and

CPP / C++ / C Code:


//file classes2.h
class Ccalc{
	int x,y;
	
	public:
	int sum(int, int);
	int sum(Cvalues&); <-- Here is my dude!
};

How can I do to classes2.h to recognize the type Cvalues of classes1.h?

Thank you.

fakepoo · #2 21-Mar-2008, 15:02

Quote:

Originally Posted by cpit

How can I do to classes2.h to recognize the type Cvalues of classes1.h?

In classes2.h, put the line:

CPP / C++ / C Code:

#include "classes1.h"

at the top of the file.

Peter_APIIT · #3 22-Mar-2008, 22:00

You also can add a forward declaration if two classes are related to each other.

class a;
class b
{
}

if class b using object of class a and vice versa.

I hope this help

sheree · #4 28-Mar-2008, 05:16

I recommand fakepoo suggestion

it is the easiest solution

C++_Bandit · #5 28-Mar-2008, 06:03

Actually, fakepoo's solution is not only easier it is the standard way you include files that you have created in any program.

Also, don't forget to optimize your code using #ifndef, you don't need to make your x and y values public since you have a function to get those values(which needs to be int so you can return them. So your final code should look like:

CPP / C++ / C Code:

//file classes1.h
#ifndef CLASSES1.H
#define CLASSES1.H

class Cvalues
{
   int x,y;

public:
   void set_values(int, int);
   int get_values();
};

#endif

CPP / C++ / C Code:


//file classes2.h
#ifndef CLASSES2.H
#define CLASSES2.H

#include "classes1.h"

class Ccalc
{
   int x,y;

public:
   int sum (int, int);
   int sum (Cvalues&);
};

#endif

These suggestions should help when you try to debug your code. I hope it makes sense.

L7Sqr · #6 28-Mar-2008, 08:44

Be careful. Most times the #include solution will work, but consider the following:

CPP / C++ / C Code:

//File one.hpp
#ifndef ONE
#define ONE
#include "two.hpp"
class One {
   Two * two;
};
#endif


//File two.hpp
#ifndef TWO
#define TWO
#include "one.hpp"
class Two {
   One * one;
};
#endif

That will not compile; you will get 'no type' errors. However, if you change both of the files so that it is a forward declaration instead of an include

CPP / C++ / C Code:

//In File one.hpp
//Change #include "two.hpp" to
class Two;

//In file two.hpp
//Change #include "one.hpp" to
class One;

You will have no trouble. The caveat is that you now have to use pointers.
It may not be often that you run into such a situation, but it does happen. And when it does, it is nice to know that you have options.

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