I can not figure out what is wrong with this header file.
#ifndef USER_H
#define USER_H
struct Node
{
User user;
Node * ptrNext;
};
class User
{
public:
User();
~User();
bool checkName( string name );
bool checkPass( string pass );
private:
string mName;
string mPass;
Node * ptrHead;
};
#endif
struct Node
{
User user;
Node * ptrNext;
};
When the compiler encounters the type User, it should give you an error because it has never seen that name before. It has no idea what you are referring to at that point. If you reverse the order of the struct and class declarations, you have the same problem because the name Node is in the class User. What to do? Think back to functions and function declarations, which are used for a similar situation.
In the case of functions that call each other(or call each other indirectly through a third function), you need to put a declaration of each function at the top of the file, and then the compiler won't complain because it has seen all the possible names before it encounters them in the functions. If you make a habit of putting function declarations at the top of the file for each of your function definitions like they teach in beginning C++ texts, then you don't have to worry about the order you define your functions, and you don't even need to know the reason for doing it.
The same type of solution applies to your header file problem. You need an incomplete User class declaration at the top of the file, so that the compiler has seen the name before it encounters it in the struct declaration:
class User;
struct Node
{
User user;
Node * ptrNext;
};
class User
{
...
...
}
That essentially tells the compiler that at some point you're going to declare a class called User and not to throw a hissy fit when it sees a variable of type User along the way. Unfortunately, the compiler is a very suspicious ogre, so if you don't include that incomplete class declaration at the top of the file, it automatically assumes you aren't ever going to declare the class, and in a regrettable act of paranoia it flags the use of a User variable as an error.
Last edited by 7stud; 04-23-2003 at 03:27 AM.
Actually I have tried to include the incomplete class declaration before the struct like you had explained but yet i get this error.
'user' uses undefined class 'User'
It is case sensitive.
It would have to be same the sameCode:'user' uses undefined class 'User'
Or simply what 7stud posted.Code:User uses
You cannot declare objects of an incomplete class; you must use pointers or references.
Last edited by Sang-drax : Tomorrow at 02:21 AM. Reason: Time travelling
Salem, thank you.
It makes complete sense now.
