C++时间和日期

C++ Date & Time

Instruction

C++标准库没有提供所谓的日期类型。C++继承了C语言用于日期和时间操作的结构和函数。
要使用日期和时间相关函数与数据结构，需要`#include <ctime>`

Data Struct & Function

Data Struct

1. 四个与时间相关的类型: clock_t, time_t, size_t, tm
2. tm struct

```
struct tm
{
int tm_sec;      // 0 - 59
int tm_min;      // 0 - 59
int tm_hour;     // 0 - 23
int tm_mday;     // 1 - 31
int tm_mon;      // 0 - 11
int tm_year;     // since 1900
int tm_wday;     // 0 - 6 (sunday = 0)
int tm_yday;     // 0 - 365
int tm_isdst;    // 夏令时
};
```

Functions

1. time_t time(time_t *time);
2. char *ctime(const time_t *time);              // Eg. Mon Apr 02 10.15.36 2018\n\0
3. struct tm *localtime(const time_t *time);
4. clock_t clock(void);
5. char *asctime(const struct tm *time);         // Eg. Mon Apr 02 10.15.36 2018\n\0
6. struct tm *gmtime(const time_t *time);
7. time_t mktime(struct tm *time);
8. double difftime(time_t time1, time_t time2);
9. size_t strftime(char *str, size_t maxsize, const char *format, const struct tm *timeptr);

10. string time format
%a      short weekday
%A      full weekday
%b      short month
%B      full month
%c      date and time   Eg. Mon Apr 02 10.15.36 2018
%d      month day
%H      24h format
%I      12h format
%j      year day
%m      month 01-12
%M      minutes 00-59
%p      AM or PM
%S      second  00-61
%U      week of year (the first day is sunday)
%w      weekday 0-6  \
%W      week of year (the first day is monday)
%x      date Eg. 08/19/12
%X      time Eg. 10.15.36
%y      short year 00-99 (since 1900)
%Y      full year
%Z      timezone name
%%      display a %