another incomplete type Error C++

Question

Possible Duplicate:
Circular Dependencies / Incomplete Types

writing a litte c++ program and be confused....

got 4 classes, 2 important for this error...

got the error message "field 'dot' has incomplete type" in Line 13 and "expected ';' befor '(' token" in same Line

The Error seems to start in the Vector3.cpp, where only the include of the Vector3.h and the empty methodes

deleted the include "Vector3.h" in the Normal3 Header, thought will be running in a circle... not so well...

some ideas? hope so :) and ty for answers

Here are my two important classes:

#ifndef NORMAL3_H
#define NORMAL3_H


class Normal3 {


      public:

      double x, y, z;
      Normal3 mul(Normal3 n);
      Normal3 add(Normal3 n);
      Normal3 dot(Vector3 v); //Line 13

      Normal3(double x = 0, double y = 0, double z = 0)
                     : x(x), y(y), z(z)
      { }   

};

#endif //NORMAL3_H

AAAAAAAAAAAAAAAAAAAAAND

#ifndef VECTOR3_H
#define VECTOR3_H

#include "Normal3.h"

class Vector3 {

      public:

      double x, y, z, magnitude;

      Vector3 add(Vector3 v);
      Vector3 add(Normal3 n);
      Vector3 sub(Normal3 n);
      Vector3 mul(double c);
      double dot(Vector3 c);
      double dot(Normal3 n);
      Vector3 normalized();
      Normal3 asNormal();
      Vector3 refelctedOn(Normal3 n);

      Vector3(double x = 0, double y = 0, double z = 0, double m = 0)
                     : x(x), y(y), z(z), magnitude(m)
      { }

};

#endif //VECTOR3_H

Wich line gives the error? line 13 where? – tobspr Oct 23 '12 at 10:24 — tobspr, Oct 23 '12 at 10:24
I don't think that normal should be a different type from – Yakov Galka Oct 23 '12 at 10:31 — Yakov Galka, Oct 23 '12 at 10:31

score 3 · Accepted Answer · edited May 23 '17 at 12:27

3

It just means that the compiler does not know what Vector3 is at that point. If you declare it in advance, the error will disappear:

#ifndef NORMAL3_H
#define NORMAL3_H

class Vector3;  // Add this line

class Normal3 {
  // ...
};

UPDATE: As john says in his comment, it would be a good improvement to replace #include "Normal3.h" in Vector3.h with just another forward declaration, class Normal3;:

#ifndef VECTOR3_H
#define VECTOR3_H

class Normal3; // instead of #include "Normal3.h"

class Vector3 {
  // ...
};

You should try to keep #include directives in your headers to a minimum in order to avoid excessive compilation dependencies. You only need to include a header if it defines a type you are using (usually because a class you are defining has a data member of this type). If you are only using pointers or references to that type or function parameters of that type (as in your example), a forward declaration is enough.

edited May 23 '17 at 12:27

Community

1
1

answered Oct 23 '12 at 10:26

Gorpik

10,940
4
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1

I'd advise a similar change to vector3.h as well. Or since both classes seems quite tightly related put both into the same header file. – john Oct 23 '12 at 10:28
1

This is a differents classes. You can not use `forward declaration` for object, only for pointers and references – Ruu Oct 23 '12 at 10:32
@Ruu: I am not sure of what you mean. I agree with john's suggestion, I am updating my answer accordingly. – Gorpik Oct 23 '12 at 10:47
Gorpik, Sorry, i made mistake. Instead `This is a differents classes` i went to say `This is a differents files` – Ruu Oct 23 '12 at 10:55
really great, working, thanks, oke, will include less includes... – Bastian Globig Oct 23 '12 at 11:00

score 0 · Answer 2 · answered Oct 23 '12 at 10:43

0

your file normal3.h nothing know about Vector3.

I see that Vector3 v does not changes into dot, then you should write:

instead Normal3 dot(Vector3 v); //Line 13

as

#ifndef NORMAL3_H
#define NORMAL3_H

class Vector3;

class Normal3 {


      public:

      double x, y, z;
      Normal3 mul(Normal3 n);
      Normal3 add(Normal3 n);
      Normal3 dot(const Vector3 &v); //Line 13

      Normal3(double x = 0, double y = 0, double z = 0)
                     : x(x), y(y), z(z)
      { }   

};

#endif //NORMAL3_H

answered Oct 23 '12 at 10:43

Ruu

1,245
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got an error free compiling!! with this and the same changes in the Methode 'add' from Normal3. Thanks, looking foreward for more code xD – Bastian Globig Oct 23 '12 at 10:52
Passing `v` as a `const` ref may be a good idea or not, depending on the actual implementation of `dot()`, but it is not necessary to solve the problem here. You can declare a function that gets a parameter of a forward declared type by value. – Gorpik Oct 23 '12 at 10:59

another incomplete type Error C++

2 Answers2