C++Talk.NET

foo · Guest

I propose that a 2 dimensional matrix be added to the standard.

The following matrix class can be used to dynamically or statically
create a 2 dimensional matrix object.
template < class T, int ROW_T = 0, int COL_T = 0 >
class matrix_2d
{
public:
matrix_2d(int row, int col):m_row(row),m_col(col),
m_data((row!=0&&col!=0)?new T[row*col]:NULL){}
matrix_2d():m_row(ROW_T),m_col(COL_T), m_data(new T[ROW_T*COL_T])
{if (!COL_T || !ROW_T) {int x[ROW_T] = {{ROW_T}};int y[COL_T] =
{{x[0]}};}}
~matrix_2d(){if(m_data) delete []m_data;}
T* operator[](int i) {return (m_data + (m_col*i));}
T const*const operator[](int i) const {return (m_data +
(m_col*i));}
private:
const int m_row;
const int m_col;
T* m_data;
};

A two dimensional object can be created with a vector<vector
type, however there are several draw backs to the vector in vector
method.
The data structure of a vector<vector>> object does not accurately
replicate a C-Style 2 dimensional array.

int MyArray[5][10]; //A single block of data is allocated for C-Style
2D array
matrix_2d<int> MyArray(5, 10); //Single block of data is allocated for
matrix_2d

vector<vector MyArray(5);//This creates an array of pointers to
an array

The vector method requires further iteration through each array to
resize it to the required 2nd dimension of a 2 dimensional array.
In the test I've conducted, the operator[] is faster in the above
matrix_2d object then in a vector<vector> > object.

The matrix_2d object also initializes faster to the two dimensional
requirements.

IMHO, the matrix_2d class does a much better job of creating a two
dimensional array then a vector<vector>> object, and it's easier to
implement.

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Thorsten Ottosen · Guest

you might want to have a look at boost::multi_array<> first,

best regards

Thorsten

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foo · Guest

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foo · Guest

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