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#include <iostream>
using namespace std;
 
template <class T>
class test {
	private:
	T a;
	public:
	test(const T &b) : a(b) {}
	friend ostream & operator << (ostream &, const test &);
};
 
ostream & operator << (ostream &out, const test &t) {
	return out<<t.a;
}
 
int main() {
	test <double> T(3.141);
	cout<<T;
	return 0;
}

prog.cpp:10:55: warning: friend declaration 'std::ostream& operator<<(std::ostream&, const test<T>&)' declares a non-template function [-Wnon-template-friend]
  friend ostream & operator << (ostream &, const test &);
                                                       ^
prog.cpp:10:55: note: (if this is not what you intended, make sure the function template has already been declared and add <> after the function name here) 
prog.cpp:13:44: error: invalid use of template-name 'test' without an argument list
 ostream & operator << (ostream &out, const test &t) {
                                            ^
prog.cpp: In function 'std::ostream& operator<<(std::ostream&, const int&)':
prog.cpp:14:16: error: request for member 'a' in 't', which is of non-class type 'const int'
  return out<<t.a;
                ^

Standard output is empty