struct timeval 和 struct timespec

DESCRIPTION
The functions gettimeofday and settimeofday can get and set the time as
well as a timezone. The tv argument is a timeval struct, as specified in <sys/time.h>:

       struct timeval {
      time_t tv_sec; /* seconds */
      suseconds_t tv_usec; /* microseconds */
};
        其中返回的timeval值为Epoch（00:00:00 1970-01-01 UTC）到创建struct timeval时的时间，tv_sec为秒数部分，tv_usec为微秒数部分（10的-6次方秒）。比如当前程序运行的tv_sec为1244770435，tv_usec为442388，即当前时间距Epoch时间1244770435秒，442388微秒。

测试代码如下：
#include <stdio.h>
#include <sys/time.h>
#include <time.h>
int gettimeofday(struct timeval *tv, struct timezone *tz);
int main(int argc,char * argv[]){
      struct timeval tv;
      while(1){
            gettimeofday(&tv,NULL);
                   printf("time %u:%u/n",tv.tv_sec,tv.tv_usec);
          sleep(2);
      }
   return 0;
}

运行结果如下：
time 1259471701:970193
time 1259471703:971529
time 1259471705:973225
time 1259471707:974921

timespec
/* POSIX.1b structure for a time value. This is like a `struct timeval' but
   has nanoseconds instead of microseconds. */
struct timespec
{
    __time_t tv_sec;        /* Seconds. */
    long int tv_nsec;       /* Nanoseconds. */
};

 

与struct timeval 不同，将结构体内成员微秒变换成纳秒