给定一个输入日期和时间(字符串格式)，我试图使用time中提供的ctime函数(例如mktime)来获取其时间。将time_t纪元时间转换回日期和时间会导致日期和时间比原始时间少一小时。我已经进行了一些讨论，这些讨论都说在夏令时的情况下可能会调整一小时。这是代码:
//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:
1.检查
tm_idst标志返回非零值，表示DST生效。但是，我怎么知道正在谈论哪个时区？2.上面给出的时间戳可能未与我所在的时区记录在一起。是否可以指定时区，以便正确设置
tm_idst标志？3.如果不确定时间戳记在哪个时区，该如何处理DST？
最佳答案
原始的C++很少包含时区数据，并且在要格式化的时间中没有时区规范，因此在某些时间段您会得到不一致的结果-例如时钟返回后的重复时间。这就是为什么始终建议在UTC中记录所有时间戳的原因-即从不将时区应用于记录的时间戳，将其记录在GMT中，然后以该值作为显示变量来回移动，这样就可以得到总计掌控。
Linux / BSD还有一些其他字段可用于确定时区以及与UTC的偏移量-例如在Linux上，它是__tm_gmtoff字段，在BSD(/ Mac OS X)中，它称为tm_gmtoff。
还有一个标记时区的附加字段，在Linux上是__tm_zone，在BSD(/ Mac OS X)中是tm_zone，但是只有在获取本地时间时才会填充该字段。
我稍微修改了您的示例，并得到以下输出:
Time entered = 2013-04-05 15:00
I am here.
Error. Check string for formatting of new date.
Details of the time structure:
Years since 1900 = 113
Months since January = 3
Day of the month = 5
Hour = 15 Minute = 0 second = 0
gmtoff = 0
Time since epoch = 1365174000
Reconverting to the time structure:
Details of the time structure:
Years since 1900 = 113
Months since January = 3
Day of the month = 5
Hour = 16 Minute = 0 second = 0
gmtoff = 3600
Zone = IST
Time in date + time = 2013-04-05 15:00 and since epoch = 1365174000
但是，如果您在Windows中使用此结构，则必须使用另一种机制，因为它没有这两个额外的字段。