问C Linux中的定时器

EN

#include<stdio.h>
#include <sys/time.h>
#include <stdlib.h>
struct timeval cur;
double time(int a);
main() {
    time(0);
    printf("%lf\n",time(1));
    sleep(3);
    printf("%lf\n",time(1));
}

double time(int a) {
    double rtime;
    if(a==0) {
        gettimeofday(&cur,NULL);
        rtime=(double)(cur.tv_sec);
        printf("%lf\n",rtime);
    } else if(a==1) {
        gettimeofday(&cur,NULL);
        return((double)(cur.tv_sec-rtime));
    }
}