Eroare de compilare: user.cpp: In function ‘int main()’: user.cpp:10:16: error: no match for ‘operator<<’ (operand types are ‘std::ifstream {aka std::basic_ifstream<char>}’ and ‘int’) OUTPUT_FILE<<x+y; ~~~~~~~~~~~^~~~~ user.cpp:10:16: note: candidate: operator<<(int, int) <built-in> user.cpp:10:16: note: no known conversion for argument 1 from ‘std::ifstream {aka std::basic_ifstream<char>}’ to ‘int’ In file included from /usr/include/c++/6/istream:39:0, from /usr/include/c++/6/fstream:38, from user.cpp:1: /usr/include/c++/6/ostream:628:5: note: candidate: template<class _CharT, class _Traits, class _Tp> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&&, const _Tp&) operator<<(basic_ostream<_CharT, _Traits>&& __os, const _Tp& __x) ^~~~~~~~ /usr/include/c++/6/ostream:628:5: note: template argument deduction/substitution failed: user.cpp:10:20: note: ‘std::ifstream {aka std::basic_ifstream<char>}’ is not derived from ‘std::basic_ostream<_CharT, _Traits>’ OUTPUT_FILE<<x+y; ^ In file included from /usr/include/c++/6/istream:39:0, from /usr/include/c++/6/fstream:38, from user.cpp:1: /usr/include/c++/6/ostream:574:5: note: candidate: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const unsigned char*) operator<<(basic_ostream<char, _Traits>& __out, const unsigned char* __s) ^~~~~~~~ /usr/include/c++/6/ostream:574:5: note: template argument deduction/substitution failed: user.cpp:10:20: note: ‘std::ifstream {aka std::basic_ifstream<char>}’ is not derived from ‘std::basic_ostream<char, _Traits>’ OUTPUT_FILE<<x+y; ^ In file included from /usr/include/c++/6/istream:39:0, from /usr/include/c++/6/fstream:38, from user.cpp:1: /usr/include/c++/6/ostream:569:5: note: candidate: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const signed char*) operator<<(basic_ostream<char, _Traits>& __out, const signed char* __s) ^~~~~~~~ /usr/include/c++/6/ostream:569:5: note: template argument deduction/substitution failed: user.cpp:10:20: note: ‘std::ifstream {aka std::basic_ifstream<char>}’ is not derived from ‘std::basic_ostream<char, _Traits>’ OUTPUT_FILE<<x+y; ^ In file included from /usr/include/c++/6/istream:39:0, from /usr/include/c++/6/fstream:38, from user.cpp:1: /usr/include/c++/6/ostream:556:5: note: candidate: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const char*) operator<<(basic_ostream<char, _Traits>& __out, const char* __s) ^~~~~~~~ /usr/include/c++/6/ostream:556:5: note: template argument deduction/substitution failed: user.cpp:10:20: note: ‘std::ifstream {aka std::basic_ifstream<char>}’ is not derived from ‘std::basic_ostream<char, _Traits>’ OUTPUT_FILE<<x+y; ^ In file included from /usr/include/c++/6/ostream:638:0, from /usr/include/c++/6/istream:39, from /usr/include/c++/6/fstream:38, from user.cpp:1: