Deletion of pointer to incomplete type 'Point'; no destructor called

Question

I have 2 files:

Point.h:

class Point {
    int x;
    int y;
    char* name;
   public:
     Point() { name = new char[5]; }
    ~Point() { delete[] name; }
};

and: Line.h:

class Point;
class Line {
    Point* p;
  public:
    Line() {
      p = new Point[2];
      ....
      ...
    }
    ~Line() {
       delete[] p;
    }
};

but when I compile, I got the next error:

deletion of pointer to incomplete type 'Point'; no destructor called

any help appreciated!

Doone

Note: std::string name; and std::array<Point, 2>. Get rid of the icky extra functions you have to take care of when dynamically allocating memory like that. – Fincher

Please see here to make this warning be treated as an error... like it should be...: #4751380 (#pragma warning (error: 4150)) – Reyna

Answer 1

You need to add #include "Point.h" into your file Line.h. You can only construct and delete complete types.

Alterntively, remove the member function definitions from Line.h, and put them in a separate file Line.cpp, and include Point.h and Line.h in that file. This is a typical dependency reduction technique which makes code faster to compile, although at a potential loss of certain inlining opportunities.

Neoterism

@vonbrand - good style dictates including it. Headers should be compilable on their own; there are fewer mysterious errors that way. – Arnettaarnette

@vonbrand - having spent most of my career writing and maintaining libraries and providing technical support, I strongly disagree. Telling users that they have to include half a dozen prerequisite headers before they can use your header is a headache, and provides no benefit to the implementor or to the user. – Arnettaarnette

@vonbrand: Honestly, after reading your comment, I can't imagine you have done any serious development in C or C++. That's just insane; of course you will often include files in a header. There is simply no way around it in real world code, and there's nothing wrong with it either. If you're writing headers that have fragile dependencies then that is the problem. – Hardandfast

So uhh... Why the heck does my code compile and run in c++ with this just being a warning? The default behavior should be to error... – Reyna

Looks like I can hack it into proper operation with this...: #4751380 (#pragma warning (error: 4150)) – Reyna

Answer 2

You have forward declared Point, which is fine for declaring a pointer or reference, but not fine for anything else in which the compiler would need to know the definition of the forward declared class.

If you need the forward declaration in the header file (do you? If not, just #include "Point.h" in Line.h ) then implement your Line functions in an implementation file which #includes Point.h.

Hardandfast

Answer 3

To expand a bit on a suggestion other people gave -- a line is always defined by two end points. There isn't much point in defining these points as a heap-allocated memory. Why not make the two points regular members of the Line class? This will save memory, improve performace and lead to a cleaner code as well. You'll have to include "Point.h" for this to work, though.

Commiserate

you're right, but this kind of simple code is where many people start learning about dynamic memory – Deprave

Answer 4

forward declaration sample with a namespace.

// my header.h
namespace Poco {
    class TextConverter;
}

Citadel