时间相关库<ctime>解析

原创作品，转载请注明来源：http://www.cnblogs.com/shrimp-can/p/5649487.html 

一、定义的类型

1.clock_t：时钟类型

2.size_t：unsigned int

3.time_t：时间类型

4.struct tm：结构，成员如下：

Member	Type	Meaning	Range
tm_sec	int	seconds after the minute	0-60*
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

二、定义的宏

1.NULL：空指针

2.CLOCKS_PER_SEC:每秒的时钟周期

三、时间操作函数

1.clock：clock_t clock (void);

返回当前时钟周期，转换为s除以CLOCKS_PER_SEC

2.difftime：double difftime (time_t end, time_t beginning);

计算geginning和end之间的时间单位秒

3.mktime：time_t mktime (struct tm * timeptr);

返回timeptr指向的时间，timeptr也会更新其他的。

  time_t rawtime;
  struct tm * timeinfo;
  int year, month ,day;
  const char * weekday[] = { "Sunday", "Monday",
                             "Tuesday", "Wednesday",
                             "Thursday", "Friday", "Saturday"};
  printf ("Enter year: "); fflush(stdout); scanf ("%d",&year);
  printf ("Enter month: "); fflush(stdout); scanf ("%d",&month);
  printf ("Enter day: "); fflush(stdout); scanf ("%d",&day);
  time ( &rawtime );
  timeinfo = localtime ( &rawtime );
  timeinfo->tm_year = year - 1900;
  timeinfo->tm_mon = month - 1;
  timeinfo->tm_mday = day;
  mktime ( timeinfo );
  printf ("That day is a %s.
", weekday[timeinfo->tm_wday]);
输出为：

Enter year: 2000
Enter month: 5
Enter day: 20
That day is a Saturday.

4.time：time_t time (time_t* timer);

得到当前的日历时间，存储在timer中，如果获取失败返回空指针，成功返回当前日历时间

四、时间转化相关函数

1.asctime：char* asctime (const struct tm * timeptr);

将tm类型的时间转化为字符串的形式，返回的字符串如Www Mmm dd hh:mm:ss yyyy

2.ctime：char* ctime (const time_t * timer);

将time_t类型的时间转化为字符串的形式，返回的字符串如：Www Mmm dd hh:mm:ss yyyy

3.gmtime：struct tm * gmtime (const time_t * timer);

将time_t的时间类型转化为UTC时间，相应的时间存储在结构tm中

4.localtime：struct tm * localtime (const time_t * timer);

使用timer中的时间填充localtime

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

将结构tm描述的时间按format格式拷贝到字符串ptr中，最大maxsize字符。formate格式如下：

  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);

 输出为：

Now it's 03:21PM.

specifier	Replaced by	Example
%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 (' ')
%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	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 (00-53)	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	%

参考：http://www.cplusplus.com/reference/ctime/