c++ 实现等待5s

#include <stdio.h>      /* puts, printf */
#include <time.h>       /* time_t, struct tm, time, localtime */
int main ()
{
    struct tm * timeinfo;
    double seconds;
    time_t start_time,now;
    
    time (&start_time);
    
    while(1){
        time (&now);
        seconds = difftime(now,start_time);
        if(seconds==5){
            break;
        }
    }
    
    timeinfo = localtime (&start_time);
    printf ("start_time local time and date: %s", asctime(timeinfo));
    timeinfo = localtime (&now);
    printf ("now local time and date: %s", asctime(timeinfo));
    
    printf("time spend %f\n",seconds);
    return 0;
}

start_time local time and date: Fri May 24 10:24:40 2019
now local time and date: Fri May 24 10:24:45 2019
time spend 5.000000