C++ tips

Define dynamic array

• To define a dynamic array

  int *p1 ;  
  p1 = new int [row] ;  
  
  // init
  for( i = 0 ; i < row ; i ++ )  
     p1[i] = rand () % 10 ;  
  
  // delete
  delete [] p1 ;
  

• To define a 2D dynamic array

  int** p2 = new int*[rows];
  for (int i = 0; i < rows; i ++) {
    p2[i] = new int[cols];
  }
  
  // init
  for(int i = 0 ; i < row ; i ++)
    for( j = 0 ; j < col ; j ++)  
        p2[i][j] = i*cols+j;  
  
  // delete
  for(int i = 0 ; i < row ; i ++)  
      delete []p2[i];  
  delete []p2;
  

• To define a 3D array

  int *** p3 ;  
  p3 = new int**[height ] ;  
  for( i = 0 ; i < height ; i ++ )  
    p3[i] = new int*[row] ;  
  for( i = 0 ; i < height ; i ++ )  
    for( j = 0 ; j < row ; j ++ )  
        p3[i][j] = new int[col] ;  
  
  // init
  for(i = 0 ; i < height ; i ++ )  
    for(j = 0 ; j < row ; j ++ )  
        for( k = 0 ; k < col ; k ++)  
            p3[i][j][k] = rand()%10 ; 
  
  // delete 
  for( i = 0 ; i < hight ; i ++ )  
    for( j = 0 ; j < row ; j ++ )  
        delete []p3[i][j] ;  
  for( i = 0 ; i < hight ; i ++ )  
    delete []p3[i] ;  
  delete []p3 ;  
  

  ​

To define a row major dynamic 2D array

int** h_data = new int*[rows];
h_data[0] = new int[rows * cols];
for (int i = 1; i < rows; ++i) 
    h_data[i] = h_data[i-1] + cols;

// init
for(int i = 0; i < rows; i++) // init
    for(int j = 0; j < cols; j++)
        h_data[i][j] = 0;

// delete
delete[] h_data[0];
delete[] h_data;