time.h 详细介绍

< ctime> (time.h)包含获得和使用日期和时间信息的函数的定义。

一、Macro constants（宏常量）

CLOCKS_PER_SEC：滴答声/秒，时间的单位
NULL：空指针

二、types（类型）

clock_t：时钟类型，表示时钟滴答数的基本数据类型
size_t：无符号整型
time_t：时间类型，表示时间
struct tm：时间结构，包含日历、时间

Member	Type	Meaning	Range
tm_sec	int	seconds	after the minute0-60*
tm_min	int	minutes	after the hour 0-59
tm_hour	int	hours	since midnight 0-23
tm_mday	int	day	of the month 1-31
tm_mon	int	months	since January 0-11
tm_year	int	years	since 1900
tm_wday	int	days	since Sunday 0-6
tm_yday	int	days	since January 1 0-365
tm_isdst	int	Daylight	Saving Time flag

三、时间操作

1、clock_t clock (void);

描述：从特定时间开始消耗的时间，如果失败，返回-1。

/* clock example: frequency of primes */
#include <stdio.h>      /* printf */
#include <time.h>       /* clock_t, clock, CLOCKS_PER_SEC */
#include <math.h>       /* sqrt */int frequency_of_primes (int n) {int i,j;int freq=n-1;for (i=2; i<=n; ++i) for (j=sqrt(i);j>1;--j) if (i%j==0) {--freq; break;}return freq;
}int main ()
{clock_t t;int f;t = clock();printf ("Calculating...\n");f = frequency_of_primes (99999);printf ("The number of primes lower than 100,000 is: %d\n",f);t = clock() - t;printf ("It took me %d clicks (%f seconds).\n",t,((float)t)/CLOCKS_PER_SEC);return 0;
}

2、double difftime (time_t end, time_t beginning);

描述：计算从beginning到end的时间(end-beginning)（单位/秒）。

/* difftime example */
#include <stdio.h>      /* printf */
#include <time.h>       /* time_t, struct tm, difftime, time, mktime */int main ()
{time_t now;struct tm newyear;double seconds;time(&now);  /* get current time; same as: now = time(NULL)  */newyear = *localtime(&now);newyear.tm_hour = 0; newyear.tm_min = 0; newyear.tm_sec = 0;newyear.tm_mon = 0;  newyear.tm_mday = 1;seconds = difftime(now,mktime(&newyear));printf ("%.f seconds since new year in the current timezone.\n", seconds);return 0;
}

3、time_t mktime (struct tm * timeptr);

描述：

返回timeptr指针描述的时间，如果时间未描述，返回-1。
localtime的逆变换
忽略结构成员tm_wday and tm_yday；其他成员及时超出有效范围，也将解释。

/* mktime example: weekday calculator */
#include <stdio.h>      /* printf, scanf */
#include <time.h>       /* time_t, struct tm, time, mktime */int main ()
{time_t rawtime;struct tm * timeinfo;int year, month ,day;const char * weekday[] = { "Sunday", "Monday","Tuesday", "Wednesday","Thursday", "Friday", "Saturday"};/* prompt user for date */printf ("Enter year: "); fflush(stdout); scanf ("%d",&year);printf ("Enter month: "); fflush(stdout); scanf ("%d",&month);printf ("Enter day: "); fflush(stdout); scanf ("%d",&day);/* get current timeinfo and modify it to the user's choice */time ( &rawtime );timeinfo = localtime ( &rawtime );timeinfo->tm_year = year - 1900;timeinfo->tm_mon = month - 1;timeinfo->tm_mday = day;/* call mktime: timeinfo->tm_wday will be set */mktime ( timeinfo );printf ("That day is a %s.\n", weekday[timeinfo->tm_wday]);return 0;
}

4、time_t time (time_t* timer);

描述：

获取当前时间。
如果时间指针不为NULL，将返回其指向的时间。
不能取得时间，返回-1.
返回的时间基于： 00:00 hours, Jan 1, 1970 UTC

/* time example */
#include <stdio.h>      /* printf */
#include <time.h>       /* time_t, struct tm, difftime, time, mktime */int main ()
{time_t timer;struct tm y2k = {0};double seconds;y2k.tm_hour = 0;   y2k.tm_min = 0; y2k.tm_sec = 0;y2k.tm_year = 100; y2k.tm_mon = 0; y2k.tm_mday = 1;time(&timer);  /* get current time; same as: timer = time(NULL)  */seconds = difftime(timer,mktime(&y2k));printf ("%.f seconds since January 1, 2000 in the current timezone", seconds);return 0;
}

四、转换

1、char* asctime (const struct tm * timeptr);

描述：

返回timeptr指针的时间，用C-字符串描述返回类型为：Www Mmm dd hh:mm:ss yyyy（星期 月 日 时分秒 年）输出在新一行，以空字符串结束

/* asctime example */
#include <stdio.h>      /* printf */
#include <time.h>       /* time_t, struct tm, time, localtime, asctime */int main ()
{time_t rawtime;struct tm * timeinfo;time ( &rawtime );timeinfo = localtime ( &rawtime );printf ( "The current date/time is: %s", asctime (timeinfo) );return 0;
}

2、char* ctime (const time_t * timer);

描述：

返回timer指针的时间，用C-字符串描述返回类型为：Www Mmm dd hh:mm:ss yyyy（星期 月 日 时分秒 年）输出在新一行，以空字符串结束和asctime(localtime(timer))一样

/* ctime example */
#include <stdio.h>      /* printf */
#include <time.h>       /* time_t, time, ctime */int main ()
{time_t rawtime;time (&rawtime);printf ("The current local time is: %s", ctime (&rawtime));return 0;
}

3、struct tm * gmtime (const time_t * timer);

描述：

利用timer填充tm结构体把time_t时间转化为UTC time

/* gmtime example */
#include <stdio.h>      /* puts, printf */
#include <time.h>       /* time_t, struct tm, time, gmtime */#define MST (-7)
#define UTC (0)
#define CCT (+8)int main ()
{time_t rawtime;struct tm * ptm;time ( &rawtime );ptm = gmtime ( &rawtime );puts ("Current time around the World:");printf ("Phoenix, AZ (U.S.) :  %2d:%02d\n", (ptm->tm_hour+MST)%24, ptm->tm_min);printf ("Reykjavik (Iceland) : %2d:%02d\n", (ptm->tm_hour+UTC)%24, ptm->tm_min);printf ("Beijing (China) :     %2d:%02d\n", (ptm->tm_hour+CCT)%24, ptm->tm_min);return 0;
}

4、struct tm * localtime (const time_t * timer);

描述：

利用timer填充tm结构体把time_t时间转化为 local time

/* localtime example */
#include <stdio.h>      /* puts, printf */
#include <time.h>       /* time_t, struct tm, time, localtime */int main ()
{time_t rawtime;struct tm * timeinfo;time (&rawtime);timeinfo = localtime (&rawtime);printf ("Current local time and date: %s", asctime(timeinfo));return 0;
}

5、·size_t strftime (char* ptr, size_t maxsize, const char* format,const struct tm* timeptr );

描述：

把timeptr中的时间，以特定的格式，复制到ptr中以format格式，复制时间timeptr到ptr，最多maxsize字符。ptr：目的数组，存储C-字符串maxsize：包括末尾空字符，复制到ptr的最大字符数format：格式返回值：返回复制到ptr的字符数（不包括末尾空字符），若超出范围maxsize，返回0

/* strftime example */
#include <stdio.h>      /* puts */
#include <time.h>       /* time_t, struct tm, time, localtime, strftime */int main ()
{time_t rawtime;struct tm * timeinfo;char buffer [80];time (&rawtime);timeinfo = localtime (&rawtime);strftime (buffer,80,"Now it's %I:%M%p.",timeinfo);puts (buffer);return 0;
}

specifier	Replaced by	Example
%a	Abbreviated	weekday name *
%A	Full weekday name *	Thursday
%b	Abbreviated month name *	Aug
%B	Full month name *	August
%c	Date and time representation *	Thu Aug 23 14:55:02 2001
%C	Year divided by 100 and truncated to integer (00-99)	20
%d	Day of the month, zero-padded (01-31)	23
%D	Short MM/DD/YY date, equivalent to %m/%d/%y	08/23/01
%e	Day of the month, space-padded ( 1-31)	23
%F	Short YYYY-MM-DD date, equivalent to %Y-%m-%d	2001-08-23
%g	Week-based year, last two digits (00-99)	01
%G	Week-based year	2001
%h	Abbreviated month name * (same as %b)	Aug