#include <sys/time.h>
#include <sys/select.h>
#include <unistd.h>
#define STDIN 0
/*標(biāo)準(zhǔn)輸入設(shè)備的描述字為0 */

main()
{
   	struct timeval tv;
	fd_set readfds;

	tv.tv_sec=2;

	tv.tv_usec=500000;
	/*設(shè)置時(shí)間片為2.5秒 */
	FD_ZERO(&readfds);
	FD_SET(STDIN,&readfds);
	/*設(shè)置讀文件集readfds為標(biāo)準(zhǔn)輸入，不關(guān)心writefds和exceptfds */
	select(STDIN+1,&readfds,NULL,NULL,&tv);

	if(FD_ISSET(STDIN,&readfds))
      		printf("A key was pressed!\n");
	else
      		printf("Timed out.\n");
}