How to simply output the current date and time in C++

Recommended study: "c Tutorial"

First introduce the 2 data types.

One is time_t, A variable related to the time function. The defined variable records the number of seconds that have passed since January 1, 1970, also known as timestamp.

The other is the structuretm,

struct tm
{
   int tm_sec;         // 秒，范围从 0 到 59
   int tm_min;         // 分，范围从 0 到 59
   int tm_hour;        // 小时，范围从 0 到 23
   int tm_mday;        // 一月中的第几天，范围从 1 到 31
   int tm_mon;         // 月份，范围从 0 到 11
   int tm_year;        // 自 1900 起的年数
   int tm_wday;        // 一周中的第几天，范围从 0 到 6
   int tm_yday;        // 一年中的第几天，范围从 0 到 365
   int tm_isdst;       // 夏令时
};

Then there are three functions related to time processing,

time_t time(time_t *time);

Generally, time(NULL) can be used to get the timestamp of the current time zone.

struct tm *localtime(const time_t *timer);

Convert time_t type to pointer of tm structure of local time.

size_t strftime(char *str, size_t maxsize, const char *format, const struct tm *timeptr)

str -- This is a pointer to the destination array to which the resulting C string will be copied.

maxsize -- This is the maximum number of characters to be copied to str.

format -- This is a C string containing any combination of ordinary characters and special format specifiers. These format specifiers are replaced by the function with corresponding values ​​representing the times specified in tm.

Format specifier:

Abbreviated month nameMar##%B%c##%d1405 231AM or PM name##%S Seconds (00-61) %UThe number of weeks in the year, with the first Sunday as the first day of the first week (00-53)Decimal number representation Day of the week, Sunday is represented as 0 (0-6) 08/19/12%X02:50:06Year, last two digits (00-99) 01Year

Specifier	Meaning	Instance
##%a	Abbreviated day of the week name	Sun
%A	Full day of the week name	Sunday
##%b
##Full month name	March
Date and time representation	Sun Aug 19 02 :56:02 2012
The day of the month ( 01-31)	19	##%H
Hour in 24 hour format (00-23)		% I
Hour in 12-hour format (01-12)		%j
Day of the year (001-366)		##%m
The month represented by decimal number (01-12) 08		%M
Points (00-59) 55		##%p
PM
02
33	##%w
4	##%W	The number of weeks in the year, with the first Monday as the first day of the first week (00-53)
34	##%x	##Date representation
		Time representation
##%y
%Y			2012
%Z	时区的名称或缩写	CDT
%%	一个 % 符号	%

4行代码实现在屏幕输出当前时间：

char str[50];
time_t now = time(NULL);
strftime(str, 50, "%x %X", localtime(&now));
cout << str << endl;

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