Unix时间戳转换date time格式

2017-07-29

unix 时间戳(unix timestamp) 也叫unix时间(unix time)，是unix系统，类unix系统的一种时间表示方式，指的是：从格林威治时间1970年01月01日00时00分00秒起至现在的总秒数。
Note: 内核版本比较低的Linux系统由于将Unix时间戳存储为32位，它能被表示的最后时间是2038年1月19日03:14:07（UTC），因此会导致2038年问题。
Unix时间戳有10位（秒级），也有13位（毫秒级），也有19位（纳秒级）等。
eg.

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unix time: 1501292159   # 秒级：10位   
可以转换成
date time: 2017/7/29 9:35:59

首先来看下我们下面要用到的两种数据类型的定义：
unix time: time_t
date time: struct tm

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// time_t 定义
typedef	__time32_t time_t;
typedef __int32 __time32_t;
// tm 结构定义
struct tm {
        int tm_sec;     /* seconds after the minute - [0,59] */
        int tm_min;     /* minutes after the hour - [0,59] */
        int tm_hour;    /* hours since midnight - [0,23] */
        int tm_mday;    /* day of the month - [1,31] */
        int tm_mon;     /* months since January - [0,11] */
        int tm_year;    /* years since 1900 */
        int tm_wday;    /* days since Sunday - [0,6] */
        int tm_yday;    /* days since January 1 - [0,365] */
        int tm_isdst;   /* daylight savings time flag */
        };

下面给出用c++实现的两种时间格式的相互转换：

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/*
 * Learn to transform unix time step to datetime
 */
#include <iostream>
#include <ctime> 
const std::string weekdays[] = {
        "Sunday", "Monday","Tuesday","Wendsday","Thursday","Friday","Saturday"
};
tm unix_2_datetime(time_t unix_time) {
    // transform unxi time to date time
    auto tick = (time_t) unix_time;  // if your input is long long: change it to 'time_t' first
    struct tm tm_ = *localtime(&tick);
    return tm_;
}
time_t datetime_2_unix(tm date_time) {
    // tranform date time to unix time
    time_t unix_time = mktime(&date_time);
    return unix_time;
}
void learn_struct_tm(const tm date_time) {
    std::cout<<"\n#: Some members of struct 'tm': "<<std::endl;
    std::cout<<"> weekday: "<<weekdays[date_time.tm_wday]<<std::endl;
    std::cout<<"> hour: "<<date_time.tm_hour<<std::endl;
    std::cout<<"> min: "<<date_time.tm_min<<std::endl;
}
int main() {
    // get current unix time
    time_t unix_time;
    time(&unix_time);
    // transform between unix time and date time
    tm date_time = unix_2_datetime(unix_time);
    unix_time = datetime_2_unix(date_time);
    std::cout<<"#: Time format transform: "<<std::endl;
    std::cout<<"> date time is: "<<asctime(&date_time);
    std::cout<<"> unix time is: "<<unix_time<<std::endl;
    // more usage about struct tm
    learn_struct_tm(date_time);
    return 0;
}

运行结果：

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#: Time format transform:
> date time is: Sat Jul 29 10:22:44 2017
> unix time is: 1501294964
#: Some members of struct 'tm':
> weekday: Saturday
> hour: 10
> min: 22