如何将字符串正确转换为std :: chrono :: system_clock :: time_point？

Question

我已经对类似one的类似问题给出了一些好的答案。

但是我的代码似乎在一小时后将字符串转换为time_point并返回到字符串后才提供输出。

给出错误答案的代码：

#include <string>
#include <ctime>
#include <chrono>
#include <iomanip>
#include <iostream>
#include <sstream>

using date_time = std::chrono::system_clock::time_point;

std::string dateTimeToString(date_time time) {
    std::time_t now_c = std::chrono::system_clock::to_time_t(time);
    auto tm = std::localtime(&now_c);
    char buffer[32];
    std::strftime(buffer, 32, "%Y-%m-%d %H:%M:%S", tm);
    return std::string(buffer);
}

date_time stringToDateTime(const std::string &s) {
    std::tm timeDate = {};
    std::istringstream ss(s);
    ss >> std::get_time(&timeDate, "%Y-%m-%d %H:%M:%S");
    return std::chrono::system_clock::from_time_t(mktime(&timeDate));
}

int main() {
    std::string birthday = "2000-06-05 20:20:00";
    std::cout << "Two birthday dates: \n" << birthday << " \nsecond one:\n" << dateTimeToString(stringToDateTime(birthday))
              << "\n******************\n";
    return 0;
}

和输出：

两个生日日期：2000-06-05 20:20:00第二个：2000-06-05 21:20:00

---

我以为这与时区有关，但是我无法解决此问题。我的代码有什么问题？

Answer 1

您可以使用boost库进行时间管理。

看boost::date_time::parse_date(const std::string& s, int order_spec = ymd_order_iso)：

//! Generic function to parse a delimited date (eg: 2002-02-10)
/*! Accepted formats are: "2003-02-10" or " 2003-Feb-10" or
 * "2003-Feburary-10"
 * The order in which the Month, Day, & Year appear in the argument
 * string can be accomodated by passing in the appropriate ymd_order_spec
 */

并且在boost::date_time::parse_delimited_time_duration(const std::string& s)：

//! Creates a time_duration object from a delimited string
/*! Expected format for string is "[-]h[h][:mm][:ss][.fff]".
 * If the number of fractional digits provided is greater than the 
 * precision of the time duration type then the extra digits are 
 * truncated.
 *
 * A negative duration will be created if the first character in
 * string is a '-', all other '-' will be treated as delimiters.
 * Accepted delimiters are "-:,.". 
 */

Boost为这两种方法都提供了包装器功能，可以解析日期时间字符串：

template<class time_type>
inline time_type parse_delimited_time(const std::string& s, char sep) {
    typedef typename time_type::time_duration_type time_duration;
    typedef typename time_type::date_type date_type;

    //split date/time on a unique delimiter char such as ' ' or 'T'
    std::string date_string, tod_string;
    split(s, sep, date_string, tod_string);
    //call parse_date with first string
    date_type d = parse_date<date_type>(date_string);
    //call parse_time_duration with remaining string
    time_duration td = parse_delimited_time_duration<time_duration>(tod_string);
    //construct a time
    return time_type(d, td);

}

如果您想要一个不同的日期格式解析器，我做了一个稍微不同的实现：

posix_time::ptime parse_dmy_time(const std::string &s, char sep) {
    typedef typename posix_time::ptime::time_duration_type time_duration;
    typedef typename posix_time::ptime::date_type date_type;

    //split date/time on a unique delimiter char such as ' ' or 'T'
    std::string date_string, tod_string;
    split(s, sep, date_string, tod_string);
    //call parse_date with first string
    auto d = parse_date<date_type>(date_string, ymd_order_dmy);
    //call parse_time_duration with remaining string
    auto td = parse_delimited_time_duration<time_duration>(tod_string);
    //construct a time
    return {d, td};
}

Answer 2

不确定是否有帮助，但对我有用。在两个步骤中添加UTC偏移量和TZ信息（%z和%Z）：

std::string dateTimeToString(date_time time) {
    std::time_t now_c = std::chrono::system_clock::to_time_t(time);
    auto tm = std::localtime(&now_c);
    char buffer[32];
    std::strftime(buffer, 32, "%Y-%m-%d %H:%M:%S%z %Z", tm);
    return std::string(buffer);
}

date_time stringToDateTime(const std::string& s) {
    std::tm timeDate = {};
    std::istringstream ss(s);
    ss >> std::get_time(&timeDate, "%Y-%m-%d %H:%M:%S%z %Z");
    return std::chrono::system_clock::from_time_t(mktime(&timeDate));
}