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c++iostreamistream

no operator >> matches these operands

I've been trying to overload the >> operator. I have a class that has two private variables:

Class Complex
{
 private:
    double real;
    double imaginary;
};

In addition I have a friend function that overloads the >> operator:

friend istream & operator>>(istream &is, Complex &c)

In the implementation of the function I've tried many ways to write into the variable of object c but I keep getting an error no operator >> matches these operands

I looked around and read that I need to write into a reference of the variable, so I tried the following:

istream & operator>>(istream &is, Complex &c)
{
using std::cout;
double &r = c.real;
cout << "real: "  << is >> r;
    return is;
}

However this still gives me the same error. I'm slightly confused as I tried is >> c.real and didn't work.

On one of the answers in a similar SO question, someone suggested writing into a local variable and setting the object variable it, something like:

double d;
cin >> d;
setReal(d);

I'm trying to find a more simpler way to achieve this rather than using a method or setting the variable to a local one.

The solution could be a simple one, but I'm really just a beginner in C++, so please take it easy on me :P.

Test case:

using std::cin;
Complex c;
cin >> c;

Exact error message:

Error   1   error C2678: binary '>>' : no operator found which takes a left-hand operand of type 'std::basic_ostream<_Elem,_Traits>' (or there is no acceptable conversion)
Solution

  • The error is on this line:

    cout << "real: "  << is >> r;

    This is interpreted as

    ((cout << "real: ") << is) >> r

    The problem here is that you can't have a line like this where you switch from outputting to cout and start reading from is. A better way to do this would be

    cout << "real: ";
is >> r;

    That said, this is a very bad idea. You should not have operator >> display a prompt, since it means that if you want to read in an object of your type from a file, every time you do so you will get the prompt "real" displayed on-screen. You should have operator >> just read the representation, and explicitly prompt before reading if that's what you want to do.

    Hope this helps!