处理夏令时c++

给定输入日期和时间(字符串格式)，我试图使用ctime(如mktime)中给出的time函数获得历元时间。将time_t历元时间转换回日期和时间会得到比原始日期和时间少一个小时的日期和时间。我已经进行了一些讨论，说可能会有一个小时的调整，以适应夏令时。下面是代码:

//sample strptime program.
#include <iostream>
#include <ctime>
#include <string>
using namespace std;
long parseTime(string time) {
  cout << "Time entered = " << time << endl;
  long timeSinceEpoch;
  struct tm t;
  if(time.find("/") != string::npos) {
    //format of date is mm/dd/yyyy. followed by clock in hh:mm (24 hour clock).
    if(strptime(time.c_str(), "%m/%e/%Y %H:%M", &t) == NULL) {
      cout << "Error. Check string for formatting." << endl;
    }
  } else if(time.find("-") != string::npos) {
    //format of date is yyyy-mm-dd hh:mm:ss (hh in 24 hour clock format).
    cout << "I am here." << endl;
    if(strptime(time.c_str(), "%Y-%m-%e %H:%M:%S", &t) == NULL) {
      cout << "Error. Check string for formatting of new date." << endl;
    }
  }
  cout << "Details of the time structure:" << endl;
  cout << "Years since 1900 = " << t.tm_year << endl;
  cout << "Months since January = " << t.tm_mon << endl;
  cout << "Day of the month = " << t.tm_mday << endl;
  cout << "Hour = " << t.tm_hour << " Minute = " << t.tm_min << " second = " << t.tm_sec << endl;
  timeSinceEpoch = mktime(&t);
  time_t temp = mktime(&t);
  cout << "Time since epoch = " << timeSinceEpoch << endl;
  cout << "Reconverting to the time structure:" << endl;
  struct tm* t2 = localtime(&temp);
  cout << "Details of the time structure:" << endl;
  cout << "Years since 1900 = " << t2->tm_year << endl;
  cout << "Months since January = " << t2->tm_mon << endl;
  cout << "Day of the month = " << t2->tm_mday << endl;
  cout << "Hour = " << t2->tm_hour << " Minute = " << t2->tm_min << " second = " << t2->tm_sec << endl;
  return timeSinceEpoch;
}
int main(int argc, char *argv[]) {
  string date, t;
  cout << "Enter date: " << endl;
  cin >> date;
  cout << "Enter time: " << endl;
  cin >> t;
  struct tm time;
  string overall = date + " " + t;
  long result = parseTime(overall);
  cout << "Time in date + time = " << overall << " and since epoch = " << result << endl;
return 0;
}

麻烦的输入是:日期:2013-03-11时间:04:41:53

我的问题(s):
1. 检查tm_idst标志返回一个非零，表示夏令时生效。但是，我如何知道正在谈论的是哪个时区呢?
2. 上面给出的时间戳可能与我所在的时区不同。是否有一种方法来指定时区，以便正确设置tm_idst标志?
3.当我不确定时间戳记录在哪个时区时，我如何处理DST ?