linux c 编程 ------ 获取时间，计算程序执行时间

#include <time.h>
#include <stdio.h>
#include <unistd.h>

int main(int argc, char argv[])
{
    time_t t;

    time(&t);
    printf(" second is %ld\n",t);

    sleep();

    t = time(NULL);
    printf(" second is %ld\n",t);

    return ;
}