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c++ dynamic 2D array

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Guest Anonymous Poster
either,


  
int* c = new int[rows*cols];
c(x,y) = c[y*rows+x]

or

  
int** c = new int*[rows];
for (int i=0; i<rows; i++)
rows[i] = new int[cols];
c(x,y) = c[x][y];


the second one is slower to init

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I believe it''s something like this (I haven''t tested this code and it has been a while since I''ve done it):


  
// to create a 10x10 matrix

int **matrix;
matrix = new int *[10];
for(int i=0; i<10; ++i)
matrix[i] = new int[10];

matrix[0][5] = 1;
//...

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The ways posted will work, but if an exception is thrown in your program between the time the array is constructed and destructed the memory will not be freed unless you add some major ''try'' - ''catch'' blocks. A way around this is to use the STL and maybe do something of the following:


  
#include <vector>

class MyArray {
private:
int numRowsC;
int numColsC;
std::vector<std::vector<int> > arrayC;
public:
MyArray(int rows, int cols) : numRowsC(rows), numColsC(cols) {
arrayC.reserve(numColsC);
for (int i=0; i<numColsC; ++i) {
arrayC.push_back(std::vector<int>());
std::vector<int> & temp = arrayC.back();
temp.reserve(numRowsC);
for (int j=0; j<numRowsC; ++j) temp.push_back(int());
}
}

std::vector<int> & operator[](int i) { return arrayC[i]; }
};


int main() {
MyArray arr(10, 10);
arr[0][0] = 5;
int junk = arr[0][0];
return 0;
}



Templatize the above (or something similar) for further ease of use.

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