Question

I have implemented a write function for my class but iam getting error:

class Fa{
private:
  string Q_;
  string F_;

public:
   void write(ostream& out = cout) const{
   out<<Q_<<endl;
   out<<F_<<endl;
   }
};

Error:default argument given for parameter 1 of `void Fa::write(std::ostream&) const’

Can anybody please tell me what does this error mean and how could i avoid it?

Answer 1

You are missing includes and namespaces:

#include <iostream>
#include <string>

class Fa{
  private:
    std::string Q_;
    std::string F_;

  public:
    void write(std::ostream& out = std::cout) const{
      out << Q_<< std::endl;
      out << F_<< std::endl;
    }
};

If you have a header and a cpp file, in the header file specify the default argument:

  /* ... */
  public:
    void write(std::ostream& out = std::cout) const;
  /* ... */

and in the cpp file do not:

    void Fa::write(std::ostream& out) const {
       /* ... */
    }