日期、时间库使用备注

日期、时间库
c/c++ 标准库
clock():返回程序消耗处理器时间
示例：

/* 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;
}

difftime:函数计算两个时间的差值

/* 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;
}

mktime:将struct tm结构转成time_t的类型。

/* 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;
}

time：获取当前时间转换成time_t 类型

/* 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;
}

转换：
asctime：转换struct tm结构 变为字符串。
示例：

/* 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;
}

ctime：将time_t 转换成字符串

/* 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;
}

gmtime：转换time_t 为 struct tm UTC 时间

/* 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;
}

localtime 函数将time_t 转换成本地struct tm结构。

/* 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;
}

strftime struct tm结构格式化时间为字符串
%a Abbreviated weekday name * Thu
%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
%H Hour in 24h format (00-23) 14
%I Hour in 12h format (01-12) 02
%j Day of the year (001-366) 235
%m Month as a decimal number (01-12) 08
%M Minute (00-59) 55
%n New-line character (’\n’)
%p AM or PM designation PM
%r 12-hour clock time * 02:55:02 pm
%R 24-hour HH:MM time, equivalent to %H:%M 14:55
%S Second (00-61) 02
%t Horizontal-tab character (’\t’)
%T ISO 8601 time format (HH:MM:SS), equivalent to %H:%M:%S 14:55:02
%u ISO 8601 weekday as number with Monday as 1 (1-7) 4
%U Week number with the first Sunday as the first day of week one (00-53) 33
%V ISO 8601 week number (01-53) 34
%w Weekday as a decimal number with Sunday as 0 (0-6) 4
%W Week number with the first Monday as the first day of week one (00-53) 34
%x Date representation * 08/23/01
%X Time representation * 14:55:02
%y Year, last two digits (00-99) 01
%Y Year 2001
%z ISO 8601 offset from UTC in timezone (1 minute=1, 1 hour=100)
If timezone cannot be determined, no characters +100
%Z Timezone name or abbreviation *
If timezone cannot be determined, no characters CDT
%% A % sign %

• The specifiers marked with an asterisk (*) are locale-dependent.
  Note: Yellow rows indicate specifiers and sub-specifiers introduced by C99. Since C99, two locale-specific modifiers can also be inserted between the percentage sign (%) and the specifier proper to request an alternative format, where applicable:
  Modifier Meaning Applies to
  E Uses the locale’s alternative representation %Ec %EC %Ex %EX %Ey %EY
  O Uses the locale’s alternative numeric symbols %Od %Oe %OH %OI %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy

示例：

/* 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;
}

c++ 库：
chrono

boost库：
date_time库
参考：https://blog.csdn.net/u010261063/article/details/86555905