Throwing values to Matrix Class?

[kindgnice]

Hello professionals,

I tried throwing values to these Matrix44 class function but I failed...

#include <iostream>
#include <cmath>

template<typename T>
class Matrix44
{
public:
	Matrix44() {}
	const T* operator [] (uint8_t i) const { return m[i]; }
	T* operator [] (uint8_t i) { return m[i]; }
	// initialize the coefficients of the matrix with the coefficients of the identity matrix
	T m[4][4] = { { 1,0,0,0 },{ 0,1,0,0 },{ 0,0,1,0 },{ 0,0,0,1 } };

	//Multiplying two-dimensional array matrices 4x4.[not yet called]
	Matrix44 operator * (const Matrix44& rhs) const
	{
		Matrix44 mult;
		for (uint8_t i = 0; i < 4; ++i) {
			for (uint8_t j = 0; j < 4; ++j) {
				mult[i][j] = m[i][0] * rhs[0][j] +
					m[i][1] * rhs[1][j] +
					m[i][2] * rhs[2][j] +
					m[i][3] * rhs[3][j];
			}
		}

		return mult;
	}

};


typedef Matrix44<float> Matrix44f;

int main() {
	std::cout << "Multiplying 2 matrices";
	std::cout << Matrix44<float>({ 1,2,3,4 }, { 5,6,7,8 }, { 9,10,11,12 }, { 13,14,15,16 }); //error
	system("pause");
	return 0;
	
}

What should I edit with my statement in line 38?

For example:

If I will multiply the matrices M1*M2 like:

M1 = | 1 2 3 4 |
| 1 2 3 4 |
| 1 2 3 4 |
| 1 2 3 4 |

M2 = | 1 2 3 4 |
| 1 2 3 4 |
| 1 2 3 4 |
| 1 2 3 4 |

I would like to ask how will I successfully throw these values to the Matrix class function above to get the answer:

M3 = | 10 20 30 40 |
| 10 20 30 40 |
| 10 20 30 40 |
| 10 20 30 40 |

[kindgnice]

I would like to ask if do I have to initialize a set of array values to rhs as well?

[JLBorges]

#include <iostream>
#include <iomanip>
#include <complex>

template< typename T > struct Matrix44
{
    // inplicitly defaulted default consteructor

    static constexpr std::size_t N = 4 ;
    using row_type = T[N] ; // a row is an array of N T

    row_type& operator[] ( std::size_t row_num ) noexcept { return m[row_num] ; }
    const row_type& operator[] ( std::size_t row_num ) const noexcept { return m[row_num] ; }

	T m[N][N] {} ; // initialise to all T{}

    // note: within the class template definition, the template name Matrix44 (without any template arguments)
    //       means Matrix44<T> (in jargon, this is known as 'the injected-class-name)
    //       the following line is equivalent to: static Matrix44<T> identity() // return an identity matrix
    static Matrix44 identity() // return an identity matrix
    {
        return
        {
            {
                { T{1}, T{},  T{},  T{} },
                { T{},  T{1}, T{},  T{} },
                { T{},  T{},  T{1}, T{} },
                { T{},  T{},  T{},  T{1} }
            }
        };
    }

    // overloaded as a non member function
    /* note: to overload as a member function, declare
       Matrix44 operator* ( const Matrix44& b ) const
       and change 'a' to '(*this)': result[i][j] += (*this)[i][k] * b[k][j];  */
    friend Matrix44 operator* ( const Matrix44& a, const Matrix44& b )
    {
        Matrix44 result ; // note: initialised to all zeroes

        for( std::size_t i = 0 ; i<N ; ++i )
            for( std::size_t j = 0 ; j<N ; ++j )
                for( std::size_t k = 0 ; k<N ; ++k )
                    result[i][j] += a[i][k] * b[k][j];

        return result ;
    }

    friend std::ostream& operator<< ( std::ostream& stm, const Matrix44& mtx )
    {
        for( std::size_t i = 0 ; i < N ; ++i )
        {
            // warning: hard-coded std::setw(16) for brevity
            for( const auto& v :  mtx[i] ) stm << std::setw(16) << v ;
            stm << '\n' ;
        }
        return stm ;
    }
};

int main()
{
    std::ios_base::Init init{} ;

    // note: { { {}, {}, {}, {}, } }
    const Matrix44<double> a { { { 1,2,3,4 }, { 5,6,7,8 }, { 9,10,11,12 }, { 13,14,15,16 } } } ;

    std::cout << a << '\n' ;
    std::cout << a * Matrix44<double>::identity() << '\n' ; // multiply with identity matrix
    std::cout << a*a << '\n' ; // multiply with itself

    Matrix44< std::complex<double> > b { { { 1,2,3,4 }, { 5,6,7,8 }, { 9,10,11,12 }, { 13,14,15,16 } } } ;
    using namespace std::literals ;
    for( std::size_t i = 0 ; i < b.N ; ++i ) for( auto& cmplx : b[i] ) cmplx += 0.1i ; 

    std::cout << b << '\n' ;
    std::cout << b * Matrix44< std::complex<double> >::identity() << '\n' ; // multiply with identity matrix
    std::cout << b*b << '\n' ; // multiply with itself
}

http://coliru.stacked-crooked.com/a/fc3915d31ca96234

[kindgnice]

Thank you @JLBorges. :)