Ошибка в конструкторе класса Book

/*эт так, для примера лишь накалякано*/
 
#include <iostream>
//#include "Library.h"
 
#include <vector>
#include <algorithm>
#include <string>
#include <iostream>
 
class Library
{
    struct Book
    {
        std::string auth;
        std::string title;
        int year;
 
        void show() const;
    };
 
    std::vector<Book> catalogue;
 
public:
 
    enum { AUTH, TITLE, YEAR };
 
    void add_book(const Book& book);
    void add_book(const std::string & auth, const std::string & title, int year);
    void show();
    void sort(int by);
};
 
//#include "Library.h"
 
void Library::Book::show() const
{
    std::cout << auth << " " << title << " " << year << "\n";
}
 
void Library::add_book(const Book& book)
{
    catalogue.push_back(book);
}
 
void Library::add_book(const std::string & auth, const std::string & title, int year)
{
    catalogue.push_back({auth, title, year});
}
 
void Library::show()
{
    for(const auto & book : catalogue)
        book.show();
}
 
void Library::sort(int by = 0)
{
    switch(by)
    {
    case AUTH:
        std::sort(catalogue.begin(), catalogue.end(), [](const Book& a, const Book& b){ return a.auth < b.auth; });
        break;
    case TITLE:
        std::sort(catalogue.begin(), catalogue.end(), [](const Book& a, const Book& b){ return a.title < b.title; });
        break;
    case YEAR:
        std::sort(catalogue.begin(), catalogue.end(), [](const Book& a, const Book& b){ return a.year < b.year; });
        break;
    default:
        break;
    }
}
 
int main()
{
    Library lib0;
 
    lib0.show();
 
    lib0.add_book({"A&B Str~", "Monday starts at saturday", 1965});
    lib0.add_book({"I.Ilf & E.Petrov", "Twelve chairs", 1928});
    lib0.add_book("A&B Str~", "Bug in the anthill", 1979);
 
    lib0.show();
    std::cout << "\n";
 
    lib0.sort(Library::TITLE);
    lib0.show();
    std::cout << "\n";
 
    lib0.sort(Library::YEAR);
    lib0.show();
    std::cout << "\n";
 
 
    lib0.add_book("B. Stroustrup", "Design and Evolution of C++", 1994);
 
    lib0.sort(Library::AUTH);
    lib0.show();
    std::cout << "\n";
 
    return 0;
}