How to custom ostream c++

Question

i have a class:

class Y{
   public:
       int x;
       Y();
};

Main:

int main(){
    Y y;
    y.x = 10;
    y << mystream;

    return 0;
}

I just wanna to cause any action when y<<mystream is typed. I tried in my class header like those:

friend Y mystream(Y y);
friend ostream mystream(ostream o, Y y)

And etc. but nothing didn't work. Any ideas to custom this stream?

Best regards!

You'll need to overload the << operator. https://stackoverflow.com/questions/476272/how-to-properly-overload-the-operator-for-an-ostream — DThought, Nov 28 '17 at 12:32
Possible duplicate of [How to properly overload the << operator for an ostream?](https://stackoverflow.com/questions/476272/how-to-properly-overload-the-operator-for-an-ostream) — YSC, Nov 28 '17 at 12:36
Why `y << stream` instead of `stream << y`, since the latter is how the `<<` operator is usually invoked on a stream. — Alnitak, Nov 28 '17 at 12:56

score 1 · Answer 1 · answered Nov 28 '17 at 12:42

1

You can overload the insertion operator "<<" to take a class A object as its LHS and an ostream object as its rhs:

class A{
    public:
        int x;

        friend ostream& operator << (A& lhs, ostream& out){
            out << lhs.x;
            return out;
        }
};



int main(){

    A a;
    a.x = 7;
    a << cout; // 7

    cout << endl;
    return 0;
}

answered Nov 28 '17 at 12:42

Raindrop7

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1

The `<<` operator should take the `ostream&` as its first parameter, not the second, so you can do `cout << a << endl`. Writing it so you do `a << cout` is wrong. – Alnitak Nov 28 '17 at 12:54
ok, I see the OP wrote it that way, so downvote reversed, but the point still remains – Alnitak Nov 28 '17 at 12:55
@Alnitak: I know but this is what the OP wanted. – Raindrop7 Nov 28 '17 at 12:55
@Alnitak: what is really wrong? In my class I am free to reverse the parameters. But I know it is something we are not used to. Especially when writing: `myClassOblj << cout << anotherValue << endl;` Yes it's unreadable. – Raindrop7 Nov 28 '17 at 13:01

score 0 · Answer 2 · answered Nov 28 '17 at 12:35

You have to overload the '<<' operator in the class then you can use it for custom output stream. Also when passing the object of ostream, make sure that they are passed by reference. You can refer to this site for example http://www.geeksforgeeks.org/overloading-stream-insertion-operators-c/

score 0 · Answer 3 · answered Nov 28 '17 at 13:32

I dont't need:

A a; cout<<a; // or a<<cout;

For example I can do this for cout in main:

    ostream& cause(ostream& out)
    {
    out<<"My stream is here";
    return out;
    }

    int main()
    {
    cout<<cause; // Print here 'my stream is here'
return 0;
    }

I just wanna get this behaviour for my class instead of std::cout, so i wanna write in main:

A a; a<<cause; // i want to manipulate stream(?)

How to custom ostream c++

3 Answers3