重载 = 运算符

Question

I wrote the following test program:

 int main(int argc, char** argv)
   {

    ifstream inFile;
    inFile.open("D:\\C++\\Assignments\\in1.txt");
    if (!inFile) {
            cout << "Unable to open file";
            exit(1); // terminate with error
    }
    Complex a,b,c;
    inFile >> a;
    inFile >> b;
    ofstream out;
    out.open("D:\\C++\\Assignments\\out1.txt");
    out << a <<endl<< b<<endl;  // dumps data to a stream connected to a file
    out << c=a <<endl;
    out.close();



  return 0;
  }

I have overloaded = as following:

  void Complex::operator=(const Complex &a)//mulptiplication
  {
    real=a.real;
    imag=a.imag;
   }

But I am getting errors like: no match for ooperator <<. Can anyone help with the error?

Answer 1

This is your problem:

out << c=a <<endl;

You need to return a Complex&

Try this:

Complex& Complex::operator=(const Complex &a)//mulptiplication
{
  real=a.real;
  imag=a.imag;

  return *this;
}

The reason is that c=a yields a void and there is no operator<< that works for void on the left hand side

Just for clarity, you might rewrite as:

c = a;
out << c << endl;

ortang is also right that there must be an operator<< for the Complex class.

Answer 2

The problem lies in out << a << endl << b << endl , since you did not overload the operator<< for the Complex class i guess.

Take a look at this SO post how to overload the operator<< .

Answer 3

If real and imag are themselves of types with correct assign semantics (for example primitive types like int or double ), then it is redundant and error-prone to implement your own operator= . Just use the compiler-generated one.

Answer 4

Even with proper operators

out << c=a <<endl;

which is parsed as

(out << c) = (a <<endl);

the error occurs, due to operator precedence.