The date and time of the C++ date

May 11, 2021 C++

3. Format the time using the structure tm

The date and time of the C+ . .

The so-called date type is not available in the standard library of C+ . T he structure and functions of the C language for date and time operations are inherited by C. In order to use date- and time-related functions and structures, you need to refer to the header file in the C++ program.

There are four time-related types: clock_t, time_t, size_t, and tm. Type clock_t, size_t, and time_t can represent system time and date as some kind of integer.

The structure type tm saves the date and time as a C structure, which is defined as follows:

struct tm {
  int tm_sec;   // 秒，正常范围从 0 到 59，但允许至 61
  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，范围从 0 到 11
  int tm_year;  // 自 1900 年起的年数
  int tm_wday;  // 一周中的第几天，范围从 0 到 6，从星期日算起
  int tm_yday;  // 一年中的第几天，范围从 0 到 365，从 1 月 1 日算起
  int tm_isdst; // 夏令时
}

Here are some important functions on dates and times in C/C. All of these functions are part of the C/C?standard library, and you can see the details of each function in the C?standard library.

Serial number	Function & Description
1	*time_t time(time_t time);** This function returns the current calendar time of the system, since the number of seconds that have passed January 1, 1970.If the system does not have time, it returns .1.
2	*char ctime(const time_t time);* This returns a string pointer indicating local time, string form day month year hours:minutes:seconds year\n 。
3	*struct tm localtime(const time_t time);* This function returns a point to representative local time. tm Structure pointer.
4	clock_t clock(void); This function returns the time (generally the beginning of the program), the time used by the processor clock.Returns .1 if time is not available.
5	*char asctime ( const struct tm * time );** This function returns a pointer to the string, and the string contains information stored in the configuration of TIME, and the return form is: DAY MONTH DATE HOURS: Minutes: seconds year \ n \ 0.
6	*struct tm gmtime(const time_t time);* This function returns a pointer to the Time, TIME is a TM structure, and is also known as the GMT time (GMT) representation with coordination world (UTC).
7	*time_t mktime(struct tm time);** This function returns to the calendar time, which is equivalent to the time stored in the structure of Time.
8	double difftime ( time_t time2, time_t time1 ); This function returns a number of seconds between TIME1 and TIME2.
9	size_t strftime(); This function can be used to format the date and time as the specified format.

The current date and time

The following example gets the date and time of the current system, including local time and coordinated world time (UTC).

#include <iostream>
#include <ctime>

using namespace std;

int main( )
{
   // 基于当前系统的当前日期/时间
   time_t now = time(0);
   
   // 把 now 转换为字符串形式
   char* dt = ctime(&now);

   cout << "本地日期和时间：" << dt << endl;

   // 把 now 转换为 tm 结构
   tm *gmtm = gmtime(&now);
   dt = asctime(gmtm);
   cout << "UTC 日期和时间："<< dt << endl;
}

When the above code is compiled and executed, it produces the following results:

本地日期和时间：Sat Jan  8 20:07:41 2011

UTC 日期和时间：Sun Jan  9 03:07:41 2011

Format the time using the structure tm

The tm structure is particularly important when dealing with date- and time-related operations in C/C. T he tm structure holds the date and time as a C structure. M ost time-related functions use the tm structure. The following example uses the tm structure and various functions related to date and time.

Before you practice using structures, you need to have a basic understanding of the C structure and how to use the arrow-gt; operator to access structure members.

#include <iostream>
#include <ctime>

using namespace std;

int main( )
{
   // 基于当前系统的当前日期/时间
   time_t now = time(0);

   cout << "1970年1月1日到目前经过的秒数:" << now << endl;

   tm *ltm = localtime(&now);

   // 输出 tm 结构的各个组成部分
   cout << "年: "<< 1900 + ltm->tm_year << endl;
   cout << "月: "<< 1 + ltm->tm_mon<< endl;
   cout << "日: "<<  ltm->tm_mday << endl;
   cout << "时间: "<< 1 + ltm->tm_hour << ":";
   cout << 1 + ltm->tm_min << ":";
   cout << 1 + ltm->tm_sec << endl;
}

When the above code is compiled and executed, it produces the following results:

1970年1月1日到目前经过的秒数:1524456057
年: 2018
月: 4
日: 23
时间: 5:1:58

The date and time of the C++ date

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