c++ - time_t转换格式问题

Question

我正在尝试创建一个易于访问的 TimeDate 变量，但在转换时遇到了问题。在 time.h 中，我如何将 time_t(自 1/1/1970 以来的秒数)转换为当前本地时区(如果适用，补偿夏令时)，以便:

time_t Seconds;

变成:

struct TimeDate
{
    short YYYY;
    unsigned char MM;
    unsigned char DD;

    unsigned char HH; //Non-DST, non-timezone, IE UTC (user has to add DST and TZO to get what they need)
    unsigned char MM;
    unsigned char S;

    char TZ[4]; //This can be optionally a larger array, null terminated preferably
    char TZO; //Timezone Offset from UTC        

    char DST; //Positive is DST (and amount of DST to apply), 0 is none, negative is unknown/error
};

在过程中不使用任何字符串文字(时区名称的条形图)(以保持高效)？这也考虑到了闰年。如果 TimeDate 可以转换回 time_t，则奖励。

Answer 1

C 标准库(可在 C++ 中使用 ctime 访问)正是为此目的提供了 localtime(或为 UTC 提供了 gmtime)。之后如果标准结构不能满足您的需求，您可以将生成的 struct tm 塞进您自己的结构中。

它没有提供的一件事是时区本身，但您可以通过使用 strftime 和 %Z 来获得它(以及 ISO 8601 格式的偏移量)和 %z 格式字符串

---

举例来说，这是一个演示此操作的程序:

#include <iostream>
#include <cstdlib>
#include <ctime>

int main(void) {
    time_t t;
    struct tm *tim;
    char tz[32];
    char ofs[32];

    std::system ("date");
    std::cout << std::endl;

    t = std::time (0);
    tim = std::localtime (&t);
    std::strftime (tz, sizeof (tz), "%Z", tim);
    std::strftime (ofs, sizeof (ofs), "%z", tim);

    std::cout << "Year:        " << (tim->tm_year + 1900) << std::endl;
    std::cout << "Month:       " << (tim->tm_mon + 1) << std::endl;
    std::cout << "Day:         " << tim->tm_mday << std::endl;
    std::cout << "Hour:        " << tim->tm_hour << std::endl;
    std::cout << "Minute:      " << tim->tm_min << std::endl;
    std::cout << "Second:      " << tim->tm_sec << std::endl;
    std::cout << "Day of week: " << tim->tm_wday << std::endl;
    std::cout << "Day of year: " << tim->tm_yday << std::endl;
    std::cout << "DST?:        " << tim->tm_isdst << std::endl;
    std::cout << "Timezone:    " << tz << std::endl;
    std::cout << "Offset:      " << ofs << std::endl;

    return 0;
}

当我在我的盒子上运行它时，我看到:

Wed Sep 28 20:45:39 WST 2011

Year:        2011
Month:       9
Day:         28
Hour:        20
Minute:      45
Second:      39
Day of week: 3
Day of year: 270
DST?:        0
Timezone:    WST
Offset:      +0800