C\C++时间处理函数[获取系统时间，求时间差，格式化输出等]

/////////////////////////////////////////////////////////
//
//  test_time.c
//
//  Copyright (C) 2011 huangkangquan@scut2008
//
//  Description: this file include the time.h, practice
//               the time type and function.
//  		 1.There types of time:
//  		 	clock_t;time_t;struct tm;
//
//  		 2.Time process function:
//  		 	clock_t clock(void);
//  		   	double difftime(time_t time1,time_t time2);
//	  		time_t mktime(struct tm * timeptr);
//  		   	time_t time(time_t *timer);
//
//  		 3.Time translation function:
//  		        char * asction(const struct tm * timeptr);
//  		        char * ctime(const time_t * timer);
//  		        struct tm * gmtime(const time_t * timer);
//                      struct tm * localtime(const time_t * timer);
//                      size_t strftime(char * restrict s,size_t maxsize,
//                      		const char * restrict format,
//                      		const struct tm  * restrict timeptr);
//
//  Sorry about my poor English,just for practicing.
//
/////////////////////////////////////////////////////////
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <windows.h>/*for Sleep*/

time_t cur_time;
time_t cur_time2;
clock_t cur_clock;  /*how much clicks since the program begin*/
struct tm * tm_time;

void get_current_time()/*get current time by three ways*/
{
cur_time = time(NULL);  /* the first method*/
time(&cur_time2); 	/*the second method*/
cur_clock = clock();	/*the third method*/
}

void display_what_can_get()
{
printf("cur_time = %g\n",(double)cur_time);
printf("cur_time2 = %g\n",(double)cur_time2);
printf("cur_clock = %g\n",(double)cur_clock);
printf("CLOCKS_PER_SEC = %g\n",(double)CLOCKS_PER_SEC);

Sleep(2000);
time_t now_time = time(NULL);
printf("Running time: %g sec.\n",difftime(now_time,cur_time));

clock_t now_clock = clock();
printf("Running time: %g sec.\n",(now_clock - cur_clock)/(double)CLOCKS_PER_SEC);
printf("Running clocks: %g times.\n",(double)(now_clock - cur_clock));
printf("CLOCKS_PER_SEC: %g\n",(double)CLOCKS_PER_SEC);

}

void display_tm(struct tm * tm_time)
{
printf("tm_year:\t%d\n",tm_time->tm_year);
printf("tm_mon :\t%d\n",tm_time->tm_mon);
printf("tm_mday:\t%d\n",tm_time->tm_mday);
printf("tm_hour:\t%d\n",tm_time->tm_hour);
printf("tm_min :\t%d\n",tm_time->tm_min);
printf("tm_sec :\t%d\n",tm_time->tm_sec);
}

void translate_type()
{
// from time_t to struct tm
//initial_tm(tm_time);
time_t my_time = time(NULL);
printf("local time:\n");
tm_time = localtime(&my_time);/*get the local time*/
display_tm(tm_time);
printf("GMT time\n");
tm_time = gmtime(&cur_time);
display_tm(tm_time);
// from struct tm to time_t
time_t time = mktime(tm_time);

// print the string
printf("%s\n",ctime(&my_time));
printf("%s\n",asctime(localtime(&my_time)));
printf("%s\n",asctime(gmtime(&my_time)));

// strftime() just like the other formate I/O function,it's complicated,because has a lot of format term.
}

int main()
{
get_current_time();
display_what_can_get();
translate_type();
return 0;
}

运行结果：



clock_t是指该程序开始启动后的时钟滴答，从上面的程序测试可看出 CLOCKS_PER_SEC 为 1000.

time_t 是一种日历时间，事实上clock_t与time_t是与实现有关的类型，可能是作为整数也可能时浮点数存储，C标准只是将其规定为“算术运算类型”，

我将它强制转为浮点输出来观察了。

struct tm 把时间分解为时分秒等，包括tm_sec,tm_min,tm_hour,tm_mday,tm_mon,tm_year,tm_wday,tm_yday,tm_isdst.

需要注意的一点是tm_mon是当前日历显示-1，比如当前是9月，此时tm_mon会是8.

localtime()产生的是本地时间，gmtime产生的是GMT（格林尼治）时间。

ctime(time_t * t)    等价于  asctime(localtime(time_t * t));

strftime()与其他格式化输入输出差不多，但转换符号是不同的。

获取时间差，可以用 difftime(time_t1,time_t2);见程序。