How can i prevent class redefinition problem ?

hi all,

suppose there are three files a.h,b.h,c.h
which contain classes a,b,c respectively.
and let c.h included in b.h and b.h included in a.h.

Code:

---

//c.h
 
class c
{ ....
};
//b.h
#include c.h
class c
{...
}
//a.h
#include b.h
#include c.h
class a
{...
}

---

On compiling there comes an error of class redeclaration ..... how can we prevent this ?

ok putting the b.h file in #ifndef ... #endif block solved the problem ... :o

Quote:

---

Originally Posted by ankurjain

hi all,

suppose there are three files a.h,b.h,c.h
which contain classes a,b,c respectively.
and let c.h included in b.h and b.h included in a.h.

Code:

---

//c.h
 
class c
{ ....
};
//b.h
#include c.h
class c
{...
}
//a.h
#include b.h
#include c.h
class a
{...
}

---

On compiling there comes an error of class redeclaration ..... how can we prevent this ?

---

The standard way is

Generic header file

Code:

---

#ifndef <FILENAME>_H
#define <FILENAME>_H
 
class <ClassName>
{
};
#endif // <FILENAME>_H

---

In example

Code:

---

// a.h
#ifndef a_h
#define a_h
 
class a
{
 
};
#endif // a_h

---

Code:

---

// b.h
#ifndef b_h
#define b_h
 
#include "a.h"
 
class b
{
 
};
#endif // b_h

---

Code:

---

// c.h
#ifndef c_h
#define c_h
 
#include "a.h"
#include "b.h"
 
class c
{
 
};
#endif // c_h

---

In this way the second inclusion of "a.h" are ignored by precompiler.

If you use Visual C++, you can also try:
#pragma once
at the top of each header file, this makes the compiler read the header just once.

Quote:

---

Originally Posted by gfunk

If you use Visual C++, you can also try:
#pragma once
at the top of each header file, this makes the compiler read the header just once.

---

Beware that this solution isn't portable.

Put all Class declaration in One generic header file.
such as:

Code:

---

//className.h
#ifndef CLASS_NAME_H
#define CLASS_NAME_H
class a;
class b;
class c;
//....
 
#endif //CLASS_NAME_H

---