operator overloading<< error

Question

Im trying to overload the operator<<

const ostream & operator<<(const ostream& out, const animal& rhs){
    out << rhs.a;
    return out;
}

it seems that im getting an error because im return a const and also because the first argument is const refrence to an ostream object.

cout << objectOfAnimal1 << objectOfAnimal2 ;

it work just fine if I change the the return type and the operator signature to this one:

ostream & operator<<(ostream& out, const animal& rhs)

You are trying to write data into the ostream, that's not a very const operation! — FatalError
– FatalError, Commented May 3, 2012 at 15:46
const means the object won't be modified; when you write cout << objectofanimal1 you are writing to the ostream that you marked as const. the compiler is smart enough to know that it can't be const — user1200540
– user1200540, Commented May 3, 2012 at 15:53
A specific question would have helped this post. We can all infer the question, but I suspect we will all infer slightly different questions. — Robᵩ
– Robᵩ, Commented May 3, 2012 at 16:11

Alok Save · Accepted Answer · 2012-05-03 15:45:59Z

4

You need to have:

ostream & operator<<(ostream& out, const animal& rhs)

In your code You are trying to modify a const ostream object, and so you get the errors.
It should not be const.

answered May 3, 2012 at 15:45

Alok Save

208k56 gold badges449 silver badges540 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

yes I know that will work, but why when I change it const it wont work. thanks

@AlexDan: The point is, it cannot be const! because you are modifying the object state.

Im not changing anything about the ostream object

@AlexDan: Yes you are. You are streaming rhs.a into it (in the expression out << rhs.a).

@AlexDan: you're feeding stream with data; when you eat a lot of donuts, you're getting fat, hence going through changes. No const, no const at all.

|

Griwes · Accepted Answer · 2012-05-03 15:45:35Z

1

ostream & operator<<(ostream& out, const animal& rhs){
out << rhs.a;
return out;
}

You've already explained what is probable reason of problem and you really didn't try it out?

answered May 3, 2012 at 15:45

Griwes

9,0892 gold badges47 silver badges71 bronze badges