field 'class' has an incompatible 'class'

Question

I get these errors:

node.h:12:2: error: 'Student' does not name a typeStudent student; 
node.h:17:14: error: 'Student' does not name a typeNode( const Student& );
node.h:20:25: error: 'Student' does not name a type
void setStudent( const Student& );
node.h:21:2: error: 'Student' does not name a type
Student getStudent() const { return student; }

this is what happens when I remove the include node.h from student.h

node.cpp:13: first defined here
node.cpp.o: In function `Node::~Node()'
node.cpp:13: multiple definition of `Node::Node()'
node.cpp:13: first defined here
node.cpp.o: In function `Node::~Node()':
node.cpp:17: multiple definition of `Node::Node(Node const&)'
main.cpp.o:node.cpp:17: first defined here
node.cpp.o: In function `Node::~Node()':
node.cpp:17: multiple definition of `Node::Node(Node const&)'
main.cpp.o:C:node.cpp:17: first defined here
node.cpp.o: In function `Node::Node(Student const&)':
node.cpp:25: multiple definition of `Node::Node(Student const&)'
node.cpp:25: first defined here

in node.h

#pragma once
#ifndef node_h
#define node_h
#include "student.h"
class Node
{
private:
   Student student; 
   Node* nextPtr;
   Node* prevPtr;
public:
   Node();
   Node( const Student& );
   Node( const Node& );
   virtual ~Node() {}
   void setStudent( const Student& );
   Student getStudent() const { return student; } //second error here
   //linked list needs to be set as a friend
   friend class dblinkedlist;
};
#endif

in student.h I do not see why this is not working properly I have tried changing the code many times, but to no avail.

  #ifndef STUDENT_H
  #define STUDENT_H
  #include <stdio.h>
  #include <string>
  #include "node.h"
  using namespace std;
 class Student 
 {
 private:
    string FirstName;
    string LastName;
    int idNumber;
    double Gpa;
 public:
    //constructors
    Student();
    Student( string, string, int, double );
    //copy construtor
    Student( const Student& );
    //destructor
    virtual ~Student(){}
    //set/get for private data
    void setidNumber( int i );
    int getidNumber() const { return idNumber; }
    void setFirstName( string );
    string getFirstName( string ) const { return FirstName; }
    void setLastName( string );
    string getLastName( string ) const { return LastName; }
    void setGpa( double g );
    double getGpa( double ) const { return Gpa; }
    void setStudent( const Student& );
    Student getStudent() const { return *this; }
    //overloaded assignment
    Student operator=( const Student& );
    //overloaded << and >>
    friend ostream& operator<<( ostream&, const Student& );
    friend istream& operator>>( istream&, Student& );
    //overloaded ==
    friend bool operator==( const Student&, const Student& );
    //make Node class a friend
    friend class Node;
  }; 
 #endif

I have tried some other methods in trying to fix the error but have come to no conclusion, any help is greatly appreciated.

If you forward-declare a class, it can only be used as a pointer or a reference. `Student student` is neither of these, and so the full definition of `Student` is required. I'd assume it's in student.h, but you didn't include this file. — Neil Kirk, Mar 24 '15 at 02:34
possible duplicate of ["Field has incomplete type" error](http://stackoverflow.com/questions/12466055/field-has-incomplete-type-error) — Neil Kirk, Mar 24 '15 at 02:35
Remove `#include "node.h"` from Student.h, that should clear things up. You can put it in Student.cpp (after including Student.h) if needed. — M.M, Mar 24 '15 at 03:03
@MattMcNabb I did exactly as you have stated but I get the error I posted above — CodeHero, Mar 24 '15 at 03:13
either you've mucked something up in your makefile / project file, or one of your files is doing `#include "node.cpp"` — M.M, Mar 24 '15 at 03:16

score 2 · Answer 1 · answered Mar 24 '15 at 02:53

The problem is that student.h includes node.h, which needs the full definition of Student, so it includes student.h, but as we are already processing student.h the header guards have been defined and nothing is there, so it continues in node.h and gets to a Student variable, but it hasn't been defined yet, because even though we started with student.h, we never actually got to the Student class.

The solution is to remove the include for node.h from student.h

I did do that but I got alot of errors. Posted above. – CodeHero Mar 24 '15 at 03:14 — CodeHero, Mar 24 '15 at 03:14

Ron Thompson · Answer 2 · 2015-03-24T02:38:37.890

1

I'm deeply confused by the two lines:

#include "student.h"
class Student;

I don't believe the second is necessary.

What this is doing is saying "hey compiler, go get the definition of the class Student from this here header file so that I can use it in this class and you'll know about its members and methods and we will both be happy" immediately followed by "hey compiler, forget about that complete class definition I just gave you, instead, I'm declaring that a class Student exists, but I'm only going to tell you more about it later". The compiler is correctly confused.

edited Mar 24 '15 at 02:38

answered Mar 24 '15 at 02:34

Ron Thompson

1,086
6
12

It gives me an error stating that Student does not name a type then if I do that – CodeHero Mar 24 '15 at 02:36
@CodeHero: Include the Student.h file and the other error message (in your main question), please. – Ron Thompson Mar 24 '15 at 02:39
@RonThompson I added my student.h file and the error I get if I remove the class Student; line – CodeHero Mar 24 '15 at 02:49

Ron Thompson · Accepted Answer · 2015-03-24T02:56:27.920

1

For your second (first?) error, you've got both headers including each other. And I don't understand why, since the only reference to Node in Student is to friend it, and the only thing Node uses from Student is get & setStudent(), which are public methods. I'd try to remove the friend class Node and the #include "node.h" to see if that makes a difference.

edited Mar 24 '15 at 02:56

answered Mar 24 '15 at 02:50

Ron Thompson

1,086
6
12

I tried removing both and it just gives me 'multiple definiton' errors – CodeHero Mar 24 '15 at 02:58
@CodeHero: Post the updated code and the new errors. We will get this. – Ron Thompson Mar 24 '15 at 03:00
@CodeHero: Also, I'm noticing your missing an `#endif` in node.h at the bottom. – Ron Thompson Mar 24 '15 at 03:06
@CodeHero: I noticed your update, which still has `class Student;` is that there in your code? – Ron Thompson Mar 24 '15 at 03:09
no it isnt in my code, I forgot to remove it there. – CodeHero Mar 24 '15 at 03:11
@CodeHero: Now the errors are referencing the node.cpp file. Gonna need to see that. You aren't including the .cpp file anywhere are you? I can't think of why it would give you multiple definitions unless you were doing that. – Ron Thompson Mar 24 '15 at 03:13
Brilliance! I did not even see I did it but I did it in my main.cpp which silly me overlooked and did for some reason. – CodeHero Mar 24 '15 at 03:16
This was my first painful lesson in C++. I vividly remember it. **NEVER INCLUDE .CPP FILES** You will have a bad day. Also, if I helped, please accept my answer :) – Ron Thompson Mar 24 '15 at 03:19

field 'class' has an incompatible 'class'

3 Answers3