ahamid555 ahamid555 - 4 years ago 135
C++ Question

list initialization for a matrix class

I am trying to write a matrix class for linear algebra calculations. I have almost finished writing what I wanted. but I have a little trouble in creating a constructor that uses list initialization to create a matrix.
this is my class data members:

template <typename T>
class Matx
{
private:
// data members
//rows and columns of matrix
int rows, cols;
//pointer to pointer to type T
T** matrix;


and this is my code for initialization:

template <typename T>
Matx<T>::Matx(T* ptM[], int m, int n) : rows(m), cols(n)
{
matrix = new T*[rows];
for (int i = 0; i < rows; i++)
matrix[i] = new T[cols];
for (int i = 0; i < rows; i++)
for (int j = 0; j < cols; j++)
matrix[i][j] = *(ptM[i] + j);
}


in main:

double mat[][5] = { {5,5,-1,7,54},{4,-9,20,12,-6},{9,-18,-3,1,21},{ 61,-8,-10,3,13 },{ 29,-28,-1,4,14 } };
double* pm[5];
for (int i=0;i<5;i++)
pm[i]=mat[i];
Matx<double> yourMat = Matx<double>(pm, 5,5);


but I think there is a better way to do it.
what I want is to be able to initialize it like arrays. something like this:

Matx<double> yourMat = { {5,5,-1,7,54},{4,-9,20,12,-6},{9,-18,-3,1,21},{ 61,-8,-10,3,13 },{ 29,-28,-1,4,14 } };


Is it possible?

Answer Source

It is definitely possible, I have made constructors that use initializer lists for similar classes. A constructor like this should do the job:

template <typename T>
Matx<T>::Matx(std::initializer_list<std::initializer_list<T>> listlist) {
    rows = (int)(listlist.begin()).size();
    cols = (int)listlist.size();

    matrix = new T*[rows];

    for (int i = 0; i < rows; i++) {
        matrix[i] = new T[cols];
        for (int j = 0; j < cols; j++) {
            matrix[i][j] = (listlist.begin()+i)[j];
        }
    }
}
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