Question

newbie here!

I am reading a code and I see the author frequently writing a member function as

const int func (const scalar& a) const
// etc

You see there are three const here, now I understand the middle one, const scalar& a, that aims to not change the object a, but what about the other two const?

Is it a good habit that I should do this all the time, to protect blahblah unchanged?

Thanks a lot!

Answer 1

The code you posted is not valid, it will not compile. However, if you consider

class MyClass {
  const int& func (const scalar& a) const {
    // ...
  }
};

The first const will specify that the return value is constant (i.e. immutable). The second const (const scalar& a) specifies that the function does not modify the value of the value of the argument a. The third const specifies that func is a constant member function, i.e. it does not modify the MyClass instance itself.