Linux-C语言中gettimeofday()函数的使用方法（转载）
1.简介：
在C语言中可以使用函数gettimeofday()函数来得到时间。它的精度可以达到微妙
2.函数原型：
#include<sys/time.h>
int gettimeofday(struct timeval*tv,struct timezone *tz )
3.说明：
gettimeofday()会把目前的时间用tv 结构体返回，当地时区的信息则放到tz所指的结构中
4.结构体：
1>timeval
struct timeval{
long tv_sec;/*秒*/
long tv_usec;/*微妙*/
}；
2>timezone 结构定义为：
struct timezone{
int tz_minuteswest;/*和greenwich 时间差了多少分钟*/
int tz_dsttime;/*type of DST correction*/
}
3>在gettimeofday()函数中tv或者tz都可以为空。如果为空则就不返回其对应的结构体。
4>函数执行成功后返回0，失败后返回-1，错误代码存于errno中。
5.程序实例：
#include<stdio.h>
#include<sys/time.h>
#include<unistd.h>
int main()
{
struct timeval tv;
struct timezone tz;
gettimeofday(&tv,&tz);
printf(“tv_sec:%d\n”,tv.tv_sec);
printf(“tv_usec:%d\n”,tv.tv_usec);
printf(“tz_minuteswest:%d\n”,tz.tz_minuteswest);
printf(“tz_dsttime:%d\n”,tz.tz_dsttime);
}
说明：在使用gettimeofday()函数时，第二个参数一般都为空，因为我们一般都只是为了获得当前时间，而不用获得timezone的数值
gettimeofday()
Get the current time
Synopsis:
#include <sys/time.h>
int gettimeofday( struct timeval * when,
void * not_used );
Arguments:
- when
- A pointer to a timeval structure where the function can store the time. The struct timeval contains the following members:
- time_t tv_sec — the number of seconds since the start of the Unix Epoch.
- suseconds_t tv_usec — the number of microseconds.
- not_used
- This pointer must be NULL or the behavior of gettimeofday() is unspecified. This argument is provided only for backwards compatibility.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
Description:
The gettimeofday() function returns the current time in when in seconds and microseconds, since the Unix Epoch, 00:00:00 January 1, 1970 Coordinated Universal Time (UTC) (formerly known as Greenwich Mean Time (GMT)).
Returns:
0 for success, or -1 if an error occurs (errno is set).
Errors:
- EFAULT
- An error occurred while accessing the when buffer.
