Function must have exactly one argument

Question

I\'ve not coded in C++ for a long time and I\'m trying to fix some old code.

I\'m geting the error:

TOutputFile& TOutputFile::operator<<(TOutpu         


        

Answer 1

Operator overloaded functions which are defined as member functions accept only one parameter. In case of overloading << operator, more than one parameter is required. Making it a friend function solves this issue.

class {
    ...
    friend TOutputFile &operator<<(TOutputFile &OutFile, const T &a);
    ...
};

template<class T>
TOutputFile &operator<<(TOutputFile &OutFile, const T &a) {
    *OutFile.FFileID << a;
    return OutFile;
}

A function marked as friend will allow that function to access private member of the class to which it is a friend.

Answer 2

Check the reference

The overloads of operator>> and operator<< that take a std::istream& or std::ostream& as the left hand argument are known as insertion and extraction operators. Since they take the user-defined type as the right argument (b in a@b), they must be implemented as non-members.

Hence, they must be non-member functions, and take exactly two arguments when they are meant to be stream operators.

If you are developing your own stream class, you can overload operator<< with a single argument as a member function. In this case, the implementation would look something like this:

template<class T>
TOutputFile &operator<<(const T& a) {
  // do what needs to be done
  return *this; // note that `*this` is the TOutputFile object as the lefthand side of <<
}