如何正确将字符串转换为标准::时间::system_clock::time_point?

How to properly convert string to std::chrono::system_clock::time_point?

本文关键字：system clock time point 时间 字符串 转换 标准 何正确      更新时间：2023-10-16

对于像这样的类似问题，我得到了一些很好的答案。

然而，我的代码似乎在将字符串time_point转换为字符串并返回字符串一小时后给出输出。

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，但我无法解决这个问题。我的代码有什么问题？

您可以使用boost库进行时间管理。

看看 boost：:d ate_time：:p arse_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
*/

在boost：:d ate_time：:p arse_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 为这两种方法制作了一个包装函数，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);
}

如果你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};
}

不确定它有帮助，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));
}
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