Question

I’ve tried many things to try and get this to work but nothing works and im really confused at what i have to do to fix this.

std::ostream& operator <<(std::ostream& os, const Book& b){
os<<b.getTitle()<<", "<<b.getYear();
return os;
}

friend std::ostream& operator<<(std::ostream&, const Book&);

and i keep getting this error

Book.cc: In function 'std::ostream& operator<<(std::ostream&, const Book&)':
Book.cc:45: error: no match for 'operator<<' in 'std::operator<< [with _CharT = char,  _Traits = std::char_traits<char>, _Alloc = std::allocator<char>](((std::basic_ostream<char,  std::char_traits<char> >&)((std::basic_ostream<char, std::char_traits<char> >*)os)), ((const  std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)((const  std::basic_string<char, std::char_traits<char>, std::allocator<char> >*)(& Book::getTitle()  const())))) << ", "'
Book.cc:44: note: candidates are: std::ostream& operator<<(std::ostream&, const Book&)

I’m really stumped at how to do this.
Thanks for the help.

Answer 1

It’s hard to tell without seeing Book, but this works [code]:

#include <string>
#include <iostream>

class Book
{
public:
  const std::string getTitle() const { return "title"; }
  const std::string getYear() const { return "year"; }
};

std::ostream& operator<<
(
  std::ostream& os,
  const Book& b
)
{
  os << b.getTitle() << ", " << b.getYear();
  return os;
}

int main()
{
  Book b;
  std::cout << b << std::endl;
}

Note that you don’t need to use friend unless operator<< needs to access non-public data or functions. How do you declare getTitle()?