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  1. #include <iostream>
  2.  
  3. using namespace std;
  4.  
  5. template <typename T>
  6. T** create2DArray(unsigned nrows, unsigned ncols)
  7. {
  8.    T** ptr = new T*[nrows];  // allocate pointers
  9.    T* pool = new T[nrows*ncols];  // allocate pool
  10.    for (unsigned i = 0; i < nrows; ++i, pool += ncols )
  11.        ptr[i] = pool;
  12.    return ptr;
  13. }
  14.  
  15. template <typename T>
  16. void delete2DArray(T** arr)
  17. {
  18.    delete [] arr[0];  // remove the pool
  19.    delete [] arr;     // remove the pointers
  20. }
  21.  
  22. int main(){
  23.  
  24.     int rows = 6;
  25.     int columns = 3;
  26.  
  27.     // allocate from the stack.
  28.     double q[rows][columns];
  29.  
  30.     // allocate from the heap.
  31.     double ** a = create2DArray<double>(rows, columns);
  32.  
  33.     // populate the arrays.
  34.     for(int i = 0; i < rows; ++i){
  35.         for(int j = 0; j < columns; ++j){
  36.             a[i][j] = columns*i+j;
  37.             q[i][j] = columns*i+j;
  38.         }
  39.     }
  40.  
  41.     cout << "*****************" << endl;
  42.     cout << "Array indexing method." << endl;
  43.     cout << "*****************" << endl;
  44.  
  45.     // print the heap allocated array using array indexing.
  46.     for(int i = 0; i < rows; ++i){
  47.         for(int j = 0; j < columns; ++j){
  48.             cout << a[i][j] << '\t';
  49.         }
  50.         cout << endl;
  51.     }
  52.  
  53.     cout << "*****************" << endl;
  54.  
  55.     // print the stack allocated array using array indexing.
  56.     for(int i = 0; i < rows; ++i){
  57.         for(int j = 0; j < columns; ++j){
  58.             cout << q[i][j] << '\t';
  59.         }
  60.         cout << endl;
  61.     }
  62.  
  63.     cout << "*****************" << endl;
  64.     cout << "Pointer dereferencing method." << endl;
  65.     cout << "*****************" << endl;
  66.  
  67.     // print the heap allocated array.
  68.     for(int i = 0; i < rows; ++i){
  69.         for(int j = 0; j < columns; ++j){
  70.             cout << *(&a[0][0] + columns*i + j) << '\t';
  71.         }
  72.         cout << endl;
  73.     }
  74.  
  75.     cout << "*****************" << endl;
  76.  
  77.     // print the stack allocated array.
  78.     for(int i = 0; i < rows; ++i){
  79.         for(int j = 0; j < columns; ++j){
  80.             cout << *(&q[0][0] + columns*i + j) << '\t';
  81.         }
  82.         cout << endl;
  83.     }
  84.     cout << "*****************" << endl;
  85.  
  86.     // release the memory allocated to the heap.
  87.     delete2DArray<double>(a);
  88.  
  89.     return 0;
  90. }
Success #stdin #stdout 0s 16064KB
comments (?)
stdin 
Standard input is empty
stdout 
*****************
Array indexing method.
*****************
0	1	2	
3	4	5	
6	7	8	
9	10	11	
12	13	14	
15	16	17	
*****************
0	1	2	
3	4	5	
6	7	8	
9	10	11	
12	13	14	
15	16	17	
*****************
Pointer dereferencing method.
*****************
0	1	2	
3	4	5	
6	7	8	
9	10	11	
12	13	14	
15	16	17	
*****************
0	1	2	
3	4	5	
6	7	8	
9	10	11	
12	13	14	
15	16	17	
*****************
https://ideone.com/f7CufD
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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