双重指针法，分配二维数组内存

#include<iostream>
 using namespace std;
 int ROW = 5;
 int COL = 5;
 int main()
 {
      int **a = new int*[ROW];
      for(int i = 0; i < ROW; i++)
          a[i] = new int[COL];
      for(int r = 0; r < ROW; r++)
          for(int c = 0; c < COL; c++)
              a[r][c] = 6;
      for(int i = 0; i < ROW; i++)
      {
          for(int j = 0; j < COL; j ++)
              cout << a[i][j] << " ";
          cout << endl;
      }
      for(int i = 0; i < ROW; i ++)
          delete[] a[i];
      delete[] a;
      int **b = NULL;
      b = (int**)malloc(sizeof(int*) * ROW);
      for(int r = 0; r < ROW; r++)
          b[r] = (int*)malloc(sizeof(int) * COL);
      for(int i = 0; i < ROW; i ++)
      {       for(int j = 0; j < COL; j++)
          {
              cout << b[i][j] << " ";
          }
          cout << endl;
      }
      for(int i = 0; i < ROW; i++)
          delete[] b[i];//这里一定要释放彻底
      delete[] b;
     return 0;