const at the end of one method giving error

Question

I don't understand why I get error with che const at the end of my method. The method print doesn't change any class member, right?

class Hello{

public:
   int get_member() {return member_;};
   void print() const {
       cout<<get_member()<<endl; 
   };

private:
   int member_;

 };

The error message is: error passing "const Hello" as "this" argument of 'int Hello:: get_member()' discards qualifiers [-fpermissive]

You are calling a non-cv qualified function from a cv-qualified one. Don't do that. Declare `get_member` as `const` which it should probably be anyway. — Captain Obvlious, Apr 10 '14 at 23:12
possible duplicate of [constant function](http://stackoverflow.com/questions/5348285/constant-function) — Jerry Coffin, Apr 10 '14 at 23:19

score 3 · Accepted Answer · answered Apr 10 '14 at 23:12

3

int get_member() const {return member_;}

Should fix it. You can't call a non-const member from a const member as it breaks the 'promise' of const. If you could there would be no guarantee that the object isn't modified during the call.

answered Apr 10 '14 at 23:12

qeadz

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Actually, you can, you just have to promise to the compiler that it's all right (casting). Reneging on the promise is punished with UB. – Deduplicator Apr 10 '14 at 23:15
You are correct that the result of calling a non-const member from a const can be achieved through casting. I'm glad you pointed it out - it's good for readers of this question to know. However I strongly feel it should be added that changing the cv qualifiers on something needs very careful consideration before being done. If at all possible, avoid doing it. – qeadz Apr 11 '14 at 00:53

const at the end of one method giving error

1 Answers1