How to properly return reference to class member?

Hi, suppose this class:

Code:

---

class Foo {
 
    protected:
    QPoint& bar() const;
 
    private:
    QPoint m_bar;
};
 
QPoint& Foo::bar() const {
    return m_bar;
}

---

I get this error:

error: invalid initialization of reference of type ‘QPoint&’ from expression of type ‘const QPoint’

However it works if I change it to this:

Code:

---

QPoint& Foo::bar() const {
    return (QPoint&) m_bar;
}

---

1) I don't understand why the compiles says my QPoint is const.
2) Is it ok to leave the cast there?

A method can't be const if it returns a non-const reference. Either make that method non-const or make the reference const. This is basic C++, you know... I'm moving the thread to a proper forum.

1. You declared the member function bar() to be const; that implies that the class and all its data members (excepting any that are declared mutable) are treated as const within that function.

2. No. You should either return a const reference, return a value instead of a reference, or remove the const specifier from the function.

Which you choose depends on how you intend the return value to be used. If you don’t have a clear reason for using a reference (const or not), for a small data structure like QPoint you should probably be returning a value.

Quote:

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Originally Posted by Coises

for a small data structure like QPoint you should probably be returning a value.

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Or a const reference.

Thank you both!