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#include <iostream>
#include <fstream>
 
using namespace std;
 
const size_t SIZE =4;
 
template<typename T>
class Matrix
{
private:
    T arr[SIZE][SIZE];
    friend  ostream& operator << (ostream &, const Matrix &);
    friend  istream& operator >> (istream &, Matrix &);
    void initialize();// функция которая заполняет матрицу как единичную
 
public:
    Matrix() {}
    Matrix(const Matrix<T>&);
    const Matrix& operator=(const Matrix<T>&);
    const Matrix& operator*(const Matrix<T>&);
    void  operator*=(const Matrix<T> &);
    T* operator[](int row);
};
 
template< typename T>
ostream & operator<<(ostream & os, const Matrix<T> & rhs)
{
    for (int i(0); i < SIZE; ++i)
    {
        for (int j(0); j < SIZE; ++j)
        {
            os << rhs.arr[i][j] << ' ';
        }
        os << endl;
    }
    return os;
}
 
template< typename T>
istream & operator>>(istream&  is, Matrix<T> & rhs)
{
    for (int i(0); i < SIZE; ++i)
    {
        for (int j(0); j < SIZE; ++j)
        {
            is >> rhs.arr[i][j];
        }
    }
    return is;
}
 
int main()
{
	Matrix <int> m;
	ifstream("input.txt") >> m;
 
	return 0;
}

prog.cpp:13:60: warning: friend declaration 'std::ostream& operator<<(std::ostream&, const Matrix<T>&)' declares a non-template function [-Wnon-template-friend]
     friend  ostream& operator << (ostream &, const Matrix &);
                                                            ^
prog.cpp:13:60: 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:14:54: warning: friend declaration 'std::istream& operator>>(std::istream&, Matrix<T>&)' declares a non-template function [-Wnon-template-friend]
     friend  istream& operator >> (istream &, Matrix &);
                                                      ^
/home/qLEnJR/ccfFikXL.o: In function `main':
prog.cpp:(.text.startup+0x34): undefined reference to `operator>>(std::istream&, Matrix<int>&)'
collect2: error: ld returned 1 exit status

Standard output is empty