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error in a simple "get-method"

General and Gameplay Programming Programming

Started by Enselic November 16, 2003 09:34 AM

4 comments, last by Enselic 20 years, 5 months ago

Enselic

829

Author

November 16, 2003 09:34 AM

This doesn''t make any sense to me. I have this:


class core_c
{
public:
    renderer_c*     rendererPointer() const;
    
private:
    renderer_c      _Renderer;
};

renderer_c* core_c :: rendererPointer() const
{
    return &_Renderer;
}

This is spitten out when I try to compile it with VC++.NET:


error C2440: ''return'' : cannot convert from ''const renderer_c *'' to ''renderer_c *'' Conversion loses qualifiers

Why is this? Taking away the const keyword is not only bad design, but it means that I have to convert more const-methods to non-consts one.

[s]--------------------------------------------------------[/s]chromecode.com - software with source code

brassfish89

122

November 16, 2003 09:41 AM

That member is const, so therefore anything it returns must be const (if you return a pointer of a member the user could modify that part of the class). Remove the const and it should work.

Enigma

1,410

November 16, 2003 09:47 AM

OK, I have to admit that I''m not fully up on how const works is situations like this, but my understanding of it is this:

1. Saying that the member function is const means you''re promising not to change any member variables.
2. Returning a pointer to a member variables means that the variable can be changed.
3. 1 & 2 conflict

To solve this you should either:

1. make the member function return type const
2. make the member function non-const

If this is wrong in anyway then please correct me,

Enigma

Enselic

829

Author

November 16, 2003 09:49 AM

Oh well, I guess I'll have to make them non-constant since the point is really just to encapsulate the core classes I have, in ONE core-class. I wonder why I didn't just make the members private in the first place since the point is that the core classes should be editable.

[edited by - Enselic on November 16, 2003 10:52:06 AM]

[s]--------------------------------------------------------[/s]chromecode.com - software with source code

Anonymous

November 16, 2003 11:08 AM

Be warned, you cant use non const member functions on const objects, you might be better off creating two of the same function, one for const, one for none const.