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(){
        time (&now);
        seconds = difftime(now,start_time);
        if(seconds==){
            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 ;
}

输出

start_time local time and date: Fri May  ::
now local time and date: Fri May  ::
time spend 5.000000