c - 用多个 if on curses 替换 switch

Question

我通过教程学习 curses 库，我在 curses 教程中用多个 if 替换了 switch 语句(switch 部分仍在注释中)，因为我更好地理解了 if 语句我的问题是，现在每次我按下一个键时，都会在新键之前使用之前输入的键，这是怎么回事？

int             main(int argc, char *argv[])
{WINDOW *my_win;
  int startx, starty, width, height;
  int ch;

  initscr();/* Start curses mode */
  cbreak();/* Line buffering disabled, Pass on                                                                   
            * everty thing to me */
  keypad(stdscr, TRUE);/* I need that nifty F1 */

  height = 3;
  width = 12;
  starty = (LINES - height) / 2;/* Calculating for a center placement */
  startx = (COLS - width) / 2;/* of the window*/
  printw("Press F1 to exit");
  refresh();
  my_win = create_newwin(height, width, starty, startx);
  /*                                                                                                             
  while((ch = getch()) != KEY_F(1))                                                                              
    {switch(ch)                                                                                                  
        {case KEY_LEFT:                                                                                          
            destroy_win(my_win);                                                                                 
            my_win = create_newwin(height, width, starty,--startx);                                              
            break;                                                                                               
        case KEY_RIGHT:                                                                                          
          destroy_win(my_win);                                                                                   
          my_win = create_newwin(height, width, starty,++startx);                                                
          break;                                                                                                 
        case KEY_UP:                                                                                             
          destroy_win(my_win);                                                                                   
          my_win = create_newwin(height, width, --starty,startx);                                                
          break;                                                                                                 
        case KEY_DOWN:                                                                                           
          destroy_win(my_win);                                                                                   
          my_win = create_newwin(height, width, ++starty,startx);                                                
          break;                                                                                                 
        }                                                                                                        
    }
  */
  while(42)
    {
      ch = getch();
    if(ch == KEY_LEFT)
      {
        destroy_win(my_win);
        my_win = create_newwin(height, width, starty,startx--);
      }
    else if(ch == KEY_RIGHT)
      {
        destroy_win(my_win);
        my_win = create_newwin(height, width, starty,startx++);
      }
    else if(ch == KEY_UP)
      {
        destroy_win(my_win);
        my_win = create_newwin(height, width, starty--,startx);
      }
    else if(ch == KEY_DOWN)
      {
        destroy_win(my_win);
        my_win = create_newwin(height, width, starty++, startx);
      }
    else
      {
        endwin();
        exit(0);
      }

  }
  endwin();/* End curses mode  */
  return 0;
}

WINDOW *create_newwin(int height, int width, int starty, int startx)
{WINDOW *local_win;

  local_win = newwin(height, width, starty, startx);
  box(local_win, 0 , 0);/* 0, 0 gives default characters                                                         
                         * for the vertical and horizontal                                                       
                         * lines*/
  wrefresh(local_win);/* Show that box */

  return local_win;
}

void destroy_win(WINDOW *local_win)
{
  /* box(local_win, ' ', ' '); : This won't produce the desired                                                  
   * result of erasing the window. It will leave it's four corners                                               
   * and so an ugly remnant of window.                                                                           
   */
  wborder(local_win, ' ', ' ', ' ',' ',' ',' ',' ',' ');
  /* The parameters taken are                                                                                    
   * 1. win: the window on which to operate                                                                      
   * 2. ls: character to be used for the left side of the window                                                 
   * 3. rs: character to be used for the right side of the window                                                
   * 4. ts: character to be used for the top side of the window                                                  
   * 5. bs: character to be used for the bottom side of the window                                               
   * 6. tl: character to be used for the top left corner of the window                                           
   * 7. tr: character to be used for the top right corner of the window                                          
   * 8. bl: character to be used for the bottom left corner of the window                                        
   * 9. br: character to be used for the bottom right corner of the window                                       
   */
  wrefresh(local_win);
  delwin(local_win);
}

Answer 1

switch 到 if 转换并不是您所做的唯一更改。您引入了如下错误，其中:

my_win = create_newwin(height, width, starty, --startx);

变成了:

my_win = create_newwin(height, width, starty, startx--);

也就是说，前缀减量变成了后缀，改变了传递给create_newwin()的值；前缀减量计算减量后的值，而后缀计算减量前的值。这意味着旧位置用于绘制窗口，产生的效果就好像错误与输入键有关，而问题实际上与输入键无关。

您对原始代码中的所有其他前缀增量执行了相同的操作。您应该将它们全部从后缀更改为前缀，代码将表现相同。