C and C++ how do I get an example of the current system time
- 2020-05-27 06:40:39
- OfStack
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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