C/C++ how do I get an example of the current system time

The system time dependent functions in the C library are defined in < time.h > In the header file, C++ is defined in < ctime > In the header file.

1. time time_t * () function

The function definition is as follows:

time_t time (time_t* timer);

Gets the unix timestamp starting at the current system calendar time UTC 1970-01-01 00:00:00

Parameter: timer access result time pointer variable of type time_t, pointer variable can be null. If the timer pointer is not null, the time() function returns a value variable that points to the same memory address as the timer pointer 1. Otherwise, if the timer pointer is null, the time() function returns an time_t variable time.

Returns value, if successful, gets the current system calendar time, otherwise returns -1.

2. Structure struct tm

变量	类型	说明	范围
tm_sec	int	每分钟的秒数	[0 - 61]
tm_min	int	每小时后面的分钟数	[0 - 59]
tm_hour	int	凌晨开始的小时数	[0 - 23]
tm_mday	int	从每月份开始算的天数	[1 - 31]
tm_mon	int	从1月份开始的月份数	[0 - 11]
tm_year	int	从1900年开始的年数
tm_wday	int	从每周天开始算的天数	[0 - 6]
tm_yday	int	1年的第几天，从零开始	[0 - 365]
tm_isdst	int	夏令时

Here are a few things to note:

1. The range of tm_sec in C89 is [0-61], which is corrected to [0-60] in C99. The usual range is [0-59], with some systems having 60-second jumps.

2. tm_mon starts from zero, so January is 0 and November 102 is 11.

3. Local time conversion function localtime(time_t*)

The function prototype

struct tm * localtime (const time_t * timer);

Convert calendar time to local time, from a timestamp starting in 1970 to a time data structure starting in 1900

4. Source code and compilation

current_time.cpp

#include <cstdio>
#include <ctime>

int main(int argc, char* argv[]) {
  time_t rawtime;
  struct tm *ptminfo;

  time(&rawtime);
  ptminfo = localtime(&rawtime);
  printf("current: %02d-%02d-%02d %02d:%02d:%02d\n",
      ptminfo->tm_year + 1900, ptminfo->tm_mon + 1, ptminfo->tm_mday,
      ptminfo->tm_hour, ptminfo->tm_min, ptminfo->tm_sec);
  return 0;
}

Compile and run

$ g++ current_time.cpp

$ ./a.out

current: 2017-07-26 23:32:46

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