Question

I am having a problem with friend functions.

I figure this is the only part of the code needed.. My problem is with this function. It says the problem is with the first line, but I don’t know how accurate that is.

friend ostream & operator << (ostream & b, Book & a)
    {
    b.setf(ios::fixed | ios::showpoint);
    b.precision(2);
    b << "Title     :  \"" << a.title << "\"\n"
    << "Author      : \"" << a.author << "\"\n"
    << "Price       : $" << a.price / 100.0 << endl
    << "Genre       : " <<a.genre << endl
    << "In stock? " << (a.status ? "yes" : "no") << endl
    << endl;
    return b;
    }

I get the errors :
lab10.cpp:95: error: can’t initialize friend function âoperator<<â

lab10.cpp:95: error: friend declaration not in class definition

Thanks in advance

Answer 1

You have to specify the function is friend of which class. You either put that function in the class declaration:

class Book{
...
  friend ostream & operator << (ostream & b, Book & a)
    {
    b.setf(ios::fixed | ios::showpoint);
    b.precision(2);
    b << "Title     :  \"" << a.title << "\"\n"
    << "Author      : \"" << a.author << "\"\n"
    << "Price       : $" << a.price / 100.0 << endl
    << "Genre       : " <<a.genre << endl
    << "In stock? " << (a.status ? "yes" : "no") << endl
    << endl;
    return b;
  }
};

The other way is to declare it as a friend inside the class, and define it in some other place:

class Book{
...
    friend ostream & operator << (ostream & b, Book & a);
};

…

// Notice, there is no "friend" in definition!
ostream & operator << (ostream & b, Book & a)
    {
    b.setf(ios::fixed | ios::showpoint);
    b.precision(2);
    b << "Title     :  \"" << a.title << "\"\n"
    << "Author      : \"" << a.author << "\"\n"
    << "Price       : $" << a.price / 100.0 << endl
    << "Genre       : " <<a.genre << endl
    << "In stock? " << (a.status ? "yes" : "no") << endl
    << endl;
    return b;
}