play_again3.c

unix linux 编程实践源代码

/* play_again3.c
 *	purpose: ask if user wants another transaction
 *	 method: set tty into chr-by-chr, no-echo mode
 *		 set tty into no-delay mode
 *		 read char, return result
 *	returns: 0=>yes, 1=>no, 2=>timeout
 *	 better: reset terminal mode on Interrupt
 */
#include	<stdio.h>
#include	<termios.h>
#include	<fcntl.h>
#include	<string.h>

#define	ASK		"Do you want another transaction"
#define	TRIES	   3	                                   /* max tries */
#define SLEEPTIME  2                                       /* time per try */
#define	BEEP       putchar('\a')                           /* alert user */

main()
{
	int	response;

	tty_mode(0);				/* save current mode	*/
	set_cr_noecho_mode();			/* set -icanon, -echo	*/
	set_nodelay_mode();			/* noinput => EOF	*/
	response = get_response(ASK, TRIES);	/* get some answer	*/
	tty_mode(1);				/* restore orig mode	*/
	return response;
}
get_response( char *question , int maxtries)
/*
 * purpose: ask a question and wait for a y/n answer or maxtries
 *  method: use getchar and complain about non-y/n input
 * returns: 0=>yes, 1=>no, 2=>timeout
 */
{
	int	input;

	printf("%s (y/n)?", question);			/* ask		*/
	fflush(stdout);					/* force output	*/
	while ( 1 ){
		sleep(SLEEPTIME);			/* wait a bit	*/
		input = tolower(get_ok_char());        	/* get next chr */
		if ( input == 'y' )
			return 0;
		if ( input == 'n' )
			return 1;
		if ( maxtries-- == 0 )			/* outatime?	*/
			return 2;			/* sayso	*/
		BEEP;
	}
}
/*
 *  skip over non-legal chars and return y,Y,n,N or EOF
 */
get_ok_char()
{
	int c;
	while( ( c = getchar() ) != EOF && strchr("yYnN",c) == NULL )
		;
	return c;
}

set_cr_noecho_mode()
/* 
 * purpose: put file descriptor 0 into chr-by-chr mode and noecho mode
 *  method: use bits in termios
 */
{
	struct	termios	ttystate;

	tcgetattr( 0, &ttystate);		/* read curr. setting	*/
	ttystate.c_lflag    	&= ~ICANON;	/* no buffering		*/
	ttystate.c_lflag    	&= ~ECHO;	/* no echo either	*/
	ttystate.c_cc[VMIN]  	=  1;		/* get 1 char at a time	*/
	tcsetattr( 0 , TCSANOW, &ttystate);	/* install settings	*/
}

set_nodelay_mode()
/*
 * purpose: put file descriptor 0 into no-delay mode
 *  method: use fcntl to set bits
 *   notes: tcsetattr() will do something similar, but it is complicated
 */
{
	int	termflags;

	termflags = fcntl(0, F_GETFL);		/* read curr. settings	*/
	termflags |= O_NDELAY;			/* flip on nodelay bit	*/
	fcntl(0, F_SETFL, termflags);		/* and install 'em	*/
}

/* how == 0 => save current mode,  how == 1 => restore mode */
/* this version handles termios and fcntl flags             */

tty_mode(int how)
{
	static struct termios original_mode;
	static int            original_flags;
	if ( how == 0 ){
		tcgetattr(0, &original_mode);
		original_flags = fcntl(0, F_GETFL);
	}
	else {
		tcsetattr(0, TCSANOW, &original_mode); 
		fcntl( 0, F_SETFL, original_flags);	
	}
}