Can someone explain the use of 'const' in this case

I was reading my C++ book for class, but it didn't tell how, or why const was used in this case:

Code:

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bool String:: operator!() const {
  return length == 0;
}

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Thanks!

Edit: Excuse the space between ":: operator" I had to put it there or the BB thought I was trying to use a smiley. lol

'const' on a member function like that is a promise that the function will not change the object to which it belongs (that is, it makes no modifications to '*this'). The one exception is that it can modify member data declared to be 'mutable'.

What does *this mean, I haven't seen it before?

I just looked up mutable. Basically, anti-const.

Quote:

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Originally posted by steve_demaio
What does *this mean, I haven't seen it before?

I just looked up mutable. Basically, anti-const.

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Well this is a pointer to the class (not the class itself, but each and every object of a class has a 'this' pointer). So *this is dereferencing the pointer (just as you might any other kind of pointer).

>>Edit: Excuse the space between ":: operator" I had to put it there or the BB thought I was trying to use a smiley. lol

You can disable smilies in a post by checking off the corresponding box below the edit-control you type your reply in...

Ahh, thank you. That's much clearer now. Here is one scenario though.

Take this function:

Code:

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double Complex::realPart() const{               
  cout << *this << endl;
  return rp;
}

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*this refers to rp in this case right?

I don't think it is possible for *this to refer to rp...I assume rp is private data:

Code:

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class Complex
{
public:
//...
double realPart() const;

private:
double rp;
};


double Complex::realPart() const
{
cout<<*this<<endl; //operator << must be overloaded for const Complex&
return rp;
}

int main()
{
Complex myComplex;
double x=myComplex.realPart();
}

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In that case *this would refer to the myComplex object...