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c++ dynamic 2D array

Started by HeadInjury11 Mar 23, 2003 at 8:21 PM 4 replies 250+ views

Original Post

HeadInjury11

Mar 23, 2003 at 8:21 PM

greetings how do I dynamically allocate memory for the rows and the columns in a 2Darray/matrix?

YoshiN

Mar 23, 2003 at 8:27 PM

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;
//...

YoshiN

Mar 23, 2003 at 8:27 PM

AP beat me to it

HeadInjury11

Author

HeadInjury11

Mar 23, 2003 at 9:05 PM

thank you very much peoples

David ONeil

Mar 24, 2003 at 9:58 AM

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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