time.h 详细介绍

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