#include        <stdio.h>
#include        <curses.h>
#include        <signal.h>
#include        <fcntl.h>
#include        <string.h>
/* some global settings main and the handler use */

#define        MESSAGE        "hello"
#define BLANK   "     "

int        row;        /* current row                */
int        col;        /* current column        */
int        dir;        /* where we are going        */
int        delay;        /* bigger => slower        */
int        done;

void        on_input(int);        /* handler for keybd    */
void        enable_kbd_signals();

int main()
{
        initscr();
        crmode();
        noecho();
        clear();

        signal(SIGIO,on_input); /* install a handler        */
        //enable_kbd_signals();   /* turn on kbd signals      */  //为什么注释掉这一句后，字符串就可以自动移动？？为什么有这句的时候，必须要按"上下左右"键才可以使得字符串进行移动？

        row   = 10;                /* start here                */
        col   = 0;
        dir   = 1;                /* add 1 to col number        */
        delay = 200;                /* 200ms = 0.2 seconds  */
        done  = 0;

        while(!done)
        {
                usleep(delay);
                move_msg();
        }
        endwin();
        return 0;
}

/*
* called after each sleep period
*/

move_msg()
{
        move( row, col );
        addstr( BLANK );
        col += dir;                        /* move to new column        */
        move( row, col );                /* then set cursor        */
        addstr( MESSAGE );                /* redo message                */
        move(0,COLS-1);
        refresh();                        /* and show it                */

        /*
         * now handle borders
         */
        if ( dir == -1 && col <= 0 )
                dir = 1;
        else if ( dir == 1 && col+strlen(MESSAGE) >= COLS )
                dir = -1;
}

/*
*  called when a keystroke appears
*/
void on_input(int signum)
{
        int        c = getch();                  /* grab the char */

        switch ( c ){
                case 'Q':
                case EOF: done = 1;
                          break;
                case ' ': dir = -dir;
                          break;
                case 'f': if ( delay > 2 )
                                  delay >>= 1;
                          break;
                case 's': delay <<= 1;
                          break;
        }
}

/*
* install a handler, tell kernel who to notify on input, enable signals
*/
void enable_kbd_signals()
{
        int  fd_flags;

        fcntl(0, F_SETOWN, getpid());
        fd_flags = fcntl(0, F_GETFL);
        fcntl(0, F_SETFL, (fd_flags|O_ASYNC));
}