I want to check lots of files which the LastWriteTimes are the same as the date of the system's yesterday or not. My question is how to set the date-time of yesterday in the SYSTEMTIME format.
The following is my code.
bool checkLastWriteTime(FILETIME ftLastWriteTime)
{
SYSTEMTIME stUTC, stLocal;
// Convert the last-write time to local time.
FileTimeToSystemTime(&ftLastWriteTime, &stUTC);
SystemTimeToTzSpecificLocalTime(NULL, &stUTC, &stLocal);
// Build a string showing the date and time.
_tprintf(TEXT("%02d/%02d/%d %02d:%02d\n"),
stLocal.wMonth, stLocal.wDay, stLocal.wYear,
stLocal.wHour, stLocal.wMinute);
SYSTEMTIME localTime;
GetLocalTime(&localTime);
//
//How to get the date of yesterday from localTime?
//
if (stLocal.wYear == localTime.wYear && stLocal.wMonth == localTime.wMonth && stLocal.wDay == localTime.wDay)
{
return true;
}
else
{
return false;
}
}
"Yesterday" is a range. It is pretty easy to calculate when it ended, that happened at 12 am this morning:
SYSTEMTIME now;
GetLocalTime(&now);
SYSTEMTIME stYesterdayEnd = { now.wYear, now.wMonth, now.wDayOfWeek, now.wDay };
FILETIME ftYesterdayEnd;
SystemTimeToFileTime(&stYesterdayEnd, &ftYesterdayEnd);
It started 24 hours before that. So you need to subtract as many 100 nanosecond units from ftYesterdayEnd. A bit tricky with FILETIME, we'll use a LARGE_INTEGER to make it easy:
LARGE_INTEGER liYesterdayBeg = { ftYesterdayEnd.dwLowDateTime, ftYesterdayEnd.dwHighDateTime };
ULONGLONG oneday = 24ULL * 60 * 60 * 1000 * 1000 * 10;
liYesterdayBeg.QuadPart -= oneday;
FILETIME ftYesterdayBeg = { liYesterdayBeg.LowPart, liYesterdayBeg.HighPart };
Now you're set to write your function:
bool wasWrittenYesterday(FILETIME ftLastWriteTime)
{
// As above
//...
return ftLastWriteTime >= ftYesterdayBeg && ftLastWriteTime < ftYesterdayEnd
}
You need to convert SYSTEMTIME to FILETIME, then subtract the day and reconvert to SYSTEMTIME.
Something like this:
FILETIME ft;
ULARGE_INTEGER uli;
__int64 oneDay;
GetLocalTime(&localTime);
SystemTimeToFileTime(&localTime, &ft);
memcpy(&uli, (ULARGE_INTEGER *)&ft, sizeof(ULARGE_INTEGER));
// get one day in 100ns parts
oneDay = (__int64)10 * (__int64)1000 * (__int64)1000;
oneDay *= (__int64)60 * (__int64)60 * (__int64)24;
// subtract one day
uli.QuadPart -= oneDay;
FileTimeToSystemTime((LPFILETIME)&uli, &localTime);
After running this code localTime contains now minus 24 hours.
See also Remarks within SYSTEMTIME reference
Related
I am trying to add days to a formatted date in C++, but without any success.
The date is passed as a SYSTEMTIME type, and days to add in long type.
In the following code example i am adding the days in a date converted to long, and this is wrong, i am using this just as an example.
long FormatDate(SYSTEMTIME* cStartTime, long daysToAdd)
{
UCHAR szToday[16];
sprintf((char*)szToday, "%04d%02d%02d", cStartTime->wYear, cStartTime->wMonth, (cStartTime->wDay));
long finalDate = atol((char*)szToday) + daysToAdd // e.g. if szToday is "20210601" and daysToAdd is 10, then finalDate is 20210611
return finalDate;
}
Thanks.
After some search and debugging i am using the following code, and it's working.
Note that hour, minute, second and millisecond from CustomDate must be set, otherwise it won't work.
In this scenario i'm adding seconds, so it could be more generic. So when i need to convert to days i do this: daysToAdd * 24 * 60 * 60.
SYSTEMTIME AddSeconds(SYSTEMTIME s, INT64 seconds) {
FILETIME f;
SystemTimeToFileTime(&s, &f);
(INT64&)f += seconds * 10000000L;
FileTimeToSystemTime(&f, &s);
return s;
}
void Func()
{
INT64 daysToAdd = 15;
SYSTEMTIME customDate;
customDate.wYear = 2021;
customDate.wMonth = 1;
customDate.wDay = 1;
customDate.wHour = 0;
customDate.wMinute = 0;
customDate.wSecond = 0;
customDate.wMilliseconds = 0;
INT64 secondsToAdd = daysToAdd * 24 * 60 * 60;
SYSTEMTIME finalDate = AddSeconds(customDate, secondsToAdd);
}
I need to take the current local time, including milliseconds, and pass it to some embedded device. This device has now idea about calendar time, but has its own timer with 1 ms accuracy. So, when this device receives the current timestamp, it opens log file and writes this timestamp to the beginning. From now, it writes different messages to the log, each one with number of milliseconds elapsed from this initial time. Finally, embedded device log file is uploaded to the host and should be parsed, with all relative time intervals converted back to full calendar time. The first part in the host program looks like this:
struct timestamp
{
int year; // 0-based
int month; // [1-12]
int day; // [1-31]
int hour; // [0-23]
int minute; // [0-59]
int sec; // [0-59]
int ms; // [0-999]
};
timestamp time_point_to_timestamp(std::chrono::time_point<std::chrono::system_clock> tp)
{
auto seconds = std::chrono::time_point_cast<std::chrono::seconds>(tp);
auto fraction = tp - seconds;
auto milliseconds = std::chrono::duration_cast<std::chrono::milliseconds>(fraction);
time_t tt = std::chrono::system_clock::to_time_t(tp);
tm* ptm = localtime(&tt);
timestamp t;
t.year = ptm->tm_year + 1900;
t.month = ptm->tm_mon + 1;
t.day = ptm->tm_mday;
t.hour = ptm->tm_hour;
t.minute = ptm->tm_min;
t.sec = ptm->tm_sec;
t.ms = static_cast<int>(milliseconds.count());
return t;
}
void start()
{
timestamp ts = time_point_to_timestamp(std::chrono::system_clock::now());
// send ts to embedded device
// ...
}
Now, when I get the log from device back to the host, it looks like this:
2018 6 24 8 25 52 598 // start time ts
500 message 1 // ms elapsed from ts
2350 message 2 // ms elapsed from ts
...
I need to parse this file and convert every message, printing its full date and time. For example, 500 will be converted to:
2018 6 24 8 25 53 098
So, I need some way to convert timestamp to any C++ type, that allows to add time intervals to it (time_point, duration?), and print it in human readable form. My compiler supports C++14.
I'd do this:
int64_t to_epoch_ms(time_point<system_clock> tp)
{
return duration_cast<milliseconds>(tp.time_since_epoch()).count();
}
Then pass the milliseconds since epoch to the device, where it can be logged as e.g. 1529819166927. Adding milliseconds is trivial and fast, whether you do it directly using the int64_t or by converting back to a time_point:
time_point<system_clock> from_epoch_ms(int64_t ms)
{
return {milliseconds(ms)};
}
auto tp1 = from_epoch_ms(ms + 123);
auto tp1 = from_epoch_ms(ms) + milliseconds(456);
Bit of a c++ newbie so here we go;
I have a method that is parsing a date/time, however that date/time is passed to me always with 00:00:00 as the hh:mm:ss. As such i want to add in the values of the current systime in place of those values. I have methods that do this, and the first method is returning the correct time in UTC format.
bool CTRHTranslationRTNS::ParseDateSysTime(const char* pszString, time_t& tValue)
{
ASSERT(pszString != NULL);
// DateTime fields.
enum { YEAR, MONTH, DAY, HOURS, MINS, SECS, NUM_FIELDS };
CStringArray astrFields;
// Split the string into the date and time fields.
int nFields = CStringParser::Split(pszString, "- :T", astrFields);
// Not DD/MM/YYYY HH:MM:SS format.
if (nFields != NUM_FIELDS)
return false;
int anFields[NUM_FIELDS] = { 0 };
// Parse field numbers.
for (int i = 0; i < NUM_FIELDS; ++i)
anFields[i] = atoi(astrFields[i]);
tm oTime = { 0 };
//Add System Time instead
time_t sysyemTimeNow;
struct tm * ptm;
time ( &sysyemTimeNow );
ptm = gmtime ( &sysyemTimeNow );
// Copy fields to time struct.
oTime.tm_mday = anFields[DAY];
oTime.tm_mon = anFields[MONTH] - 1;
oTime.tm_year = anFields[YEAR] - 1900;
oTime.tm_hour = ptm->tm_hour;
oTime.tm_min = ptm->tm_min;
oTime.tm_sec = ptm->tm_sec;
oTime.tm_isdst = -1;
// Convert to time_t.
tValue = mktime(&oTime);
// Invalid field values.
if (tValue < 0)
return false;
return true;
}
In the second method I do some formatting on the date/time and this results in 2 hours being removed from the time.
string CTRHTranslationRTNS::ConvertDateSysTimeToDateInUTC(const string& bossDate)
{
time_t dealDate;
if (ParseDateSysTime(bossDate.c_str(), dealDate))
{
struct tm * ptm = gmtime(&dealDate);
char buffer [80];
strftime(buffer,80,"%Y-%m-%d %H:%M:%S",ptm);
return string(buffer);
}
else
{
throw exception(string("Invalid date/SysTime value: ").append(bossDate).c_str());
}
}
Just to be clear, the ParseDateSysTime method returns the time with the correct UTC value of 11:53, but as soon as
struct tm * ptm = gmtime(&dealDate);
is called the time changes to 08:53. It suggests this is a product of calling the gmtime() method but i am not sure.
Many Thanks
Graham
The reson is the mktime() method used in the first function uses local time, but gmtime() uses UTC time.
See http://www.cplusplus.com/reference/clibrary/ctime/mktime/ and http://www.cplusplus.com/reference/clibrary/ctime/gmtime/ for further explanation.
Try this function:
CTime Time2UTC(CTime original)
{
CString Formatted = original.FormatGmt(L"%Y%m%d%H%M%S");
int Year, Month, Day, Hour, Minute;
if (Formatted != L"" && Formatted.GetLength() >= 12)
{
Year = _wtol(Formatted.Left(4));
Month = _wtol(Formatted.Mid(4, 2));
Day = _wtol(Formatted.Mid(6,2));
Hour = _wtol(Formatted.Mid(8, 2));
Minute = _wtol(Formatted.Mid(10, 2));
CTime result(Year, Month, Day, Hour, Minute, 0);
return result;
}
else
return (CTime)NULL;
}
I'm trying to see if WindAPIs that convert from local to UTC time and vice versa are Daylight Saving Time accurate. For instance, let's take LocalFileTimeToFileTime API. Its description states:
LocalFileTimeToFileTime uses the current settings for the time zone
and daylight saving time. Therefore, if it is daylight saving time,
this function will take daylight saving time into account, even if the
time you are converting is in standard time.
So I'm testing it with this code:
//Say, if DST change takes place on Mar-8-2015 at 2:00:00 AM
//when the clock is set 1 hr forward
//Let's check the difference between two times:
SYSTEMTIME st1_local = {2015, 3, 0, 8, 1, 30, 0, 0}; //Mar-8-2015 1:30:00 AM
SYSTEMTIME st2_local = {2015, 3, 0, 8, 3, 30, 0, 0}; //Mar-8-2015 3:30:00 AM
//Convert to file-time format
FILETIME ft1_local, ft2_local;
VERIFY(::SystemTimeToFileTime(&st1_local, &ft1_local));
VERIFY(::SystemTimeToFileTime(&st2_local, &ft2_local));
//Then convert from local to UTC time
FILETIME ft1_utc, ft2_utc;
VERIFY(::LocalFileTimeToFileTime(&ft1_local, &ft1_utc));
VERIFY(::LocalFileTimeToFileTime(&ft2_local, &ft2_utc));
//Get the difference
LONGLONG iiDiff100ns = (((LONGLONG)ft2_utc.dwHighDateTime << 32) | ft2_utc.dwLowDateTime) -
(((LONGLONG)ft1_utc.dwHighDateTime << 32) | ft1_utc.dwLowDateTime);
//Convert from 100ns to seconds
LONGLONG iiDiffSecs = iiDiff100ns / 10000000LL;
//I would expect 1 hr
ASSERT(iiDiffSecs == 3600); //But I get 7200, which is 2 hrs!
So what am I missing here?
SystemTimeToFileTime() interprets its first argument as a UTC time (which has no concept of DST), so your ft1_local and ft2_local objects will always be two hours apart since you're changing the data format, but not the actual point in time. LocalFileTimeToFileTime() will then apply the same offset to whatever you pass to it, so ft1_utc and ft2_utc will always end up two hours apart, also.
As the documentation says, "LocalFileTimeToFileTime uses the current settings for the time zone and daylight saving time" (emphasis mine), so if at the current time you're four hours behind UTC, for instance, it'll just deduct four hours from whatever time you pass to it, regardless of whether that time originally represented some time at the other side of DST.
EDIT: Per the comments, here's how you'd get the seconds difference between two local times in standard C:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main(void) {
struct tm start_time;
start_time.tm_year = 115;
start_time.tm_mon = 2;
start_time.tm_mday = 8;
start_time.tm_hour = 1;
start_time.tm_min = 30;
start_time.tm_sec = 0;
start_time.tm_isdst = -1;
struct tm end_time;
end_time.tm_year = 115;
end_time.tm_mon = 2;
end_time.tm_mday = 8;
end_time.tm_hour = 3;
end_time.tm_min = 30;
end_time.tm_sec = 0;
end_time.tm_isdst = -1;
time_t start_tm = mktime(&start_time);
time_t end_tm = mktime(&end_time);
if ( start_tm == -1 || end_tm == -1 ) {
fputs("Couldn't get local time.", stderr);
exit(EXIT_FAILURE);
}
double seconds_diff = difftime(end_tm, start_tm);
printf("There are %.1f seconds difference.\n", seconds_diff);
return EXIT_SUCCESS;
}
which outputs:
paul#thoth:~/src$ ./difftime
There are 3600.0 seconds difference.
paul#thoth:~/src$
as you're expecting.
Note that, with struct tm:
tm_year is expressed in years since 1900, so to get 2015 we write 115
tm_mon is in the range 0 though 11, so March is 2, not 3.
The other time members are as you'd expect
When tm_isdst is set to -1, mktime() will attempt to find out for itself whether DST was in effect at the local time we supplied, which is what we want it to do, here.
In despite of all the beauty of Paul Griffiths' solution, I can't use it due to an apparent locale limitation. (C is obviously showing its age.) So I had to go with a pure WinAPI approach. Next is what I came up with. Correct me if I'm wrong (especially people with access to time zones other than the US one that Microsoft's mktime seems to be favoring):
SYSTEMTIME st1 = {2015, 3, 0, 8, 1, 30, 0, 0}; //Mar-8-2015 1:30:00 AM
SYSTEMTIME st2 = {2015, 3, 0, 8, 3, 30, 0, 0}; //Mar-8-2015 3:30:00 AM
LONGLONG iiDiffNs;
if(GetLocalDateTimeDifference(&st1, &st2, &iiDiffNs))
{
_tprintf(L"Difference is %.02f sec\n", (double)iiDiffNs / 1000.0);
}
else
{
_tprintf(L"ERROR (%d) calculating the difference.\n", ::GetLastError());
}
Then this is the actual implementation. One important aspect to note here is that the method below may not work reliably on Windows XP due to the lack of APIs to retrieve time zone info for a specific year.
Some declarations first:
enum DST_STATUS{
DST_ERROR = TIME_ZONE_ID_INVALID, //Error
DST_NONE = TIME_ZONE_ID_UNKNOWN, //Daylight Saving Time is NOT observed
DST_OFF = TIME_ZONE_ID_STANDARD, //Daylight Saving Time is observed, but the system is currently not on it
DST_ON = TIME_ZONE_ID_DAYLIGHT, //Daylight Saving Time is observed, and the system is currently on it
};
#define FILETIME_TO_100NS(f) (((LONGLONG)f.dwHighDateTime << 32) | f.dwLowDateTime)
BOOL GetLocalDateTimeDifference(SYSTEMTIME* pStBegin_Local, SYSTEMTIME* pStEnd_Local, LONGLONG* pOutDiffMs = NULL);
BOOL ConvertLocalTimeToUTCTime(SYSTEMTIME* pSt_Local, SYSTEMTIME* pOutSt_UTC = NULL);
DST_STATUS GetDSTInfoForYear(USHORT uYear, TIME_ZONE_INFORMATION* pTZI = NULL);
And the implementation:
BOOL GetLocalDateTimeDifference(SYSTEMTIME* pStBegin_Local, SYSTEMTIME* pStEnd_Local, LONGLONG* pOutDiffMs)
{
//Calculate difference between two local dates considering DST adjustments between them
//INFO: May not work correctly on Windows XP for a year other than the current year!
//'pStBegin_Local' = local date/time to start from
//'pStEnd_Local' = local date/time to end with
//'pOutDiffMs' = if not NULL, receives the difference in milliseconds (if success)
//RETURN:
// = TRUE if success
// = FALSE if error (check GetLastError() for info)
BOOL bRes = FALSE;
LONGLONG iiDiffMs = 0;
int nOSError = NO_ERROR;
if(pStBegin_Local &&
pStEnd_Local)
{
//Convert both dates to UTC
SYSTEMTIME stBeginUTC;
if(ConvertLocalTimeToUTCTime(pStBegin_Local, &stBeginUTC))
{
SYSTEMTIME stEndUTC;
if(ConvertLocalTimeToUTCTime(pStEnd_Local, &stEndUTC))
{
//Then convert into a more manageable format: FILETIME
//It will represent number of 100-nanosecond intervals since January 1, 1601 for each date
FILETIME ftBeginUTC;
if(::SystemTimeToFileTime(&stBeginUTC, &ftBeginUTC))
{
FILETIME ftEndUTC;
if(::SystemTimeToFileTime(&stEndUTC, &ftEndUTC))
{
//Now get the difference in ms
//Convert from 100-ns intervals = 10^7, where ms = 10^3
iiDiffMs = (FILETIME_TO_100NS(ftEndUTC) - FILETIME_TO_100NS(ftBeginUTC)) / 10000LL;
//Done
bRes = TRUE;
}
else
nOSError = ::GetLastError();
}
else
nOSError = ::GetLastError();
}
else
nOSError = ::GetLastError();
}
else
nOSError = ::GetLastError();
}
else
nOSError = ERROR_INVALID_PARAMETER;
if(pOutDiffMs)
*pOutDiffMs = iiDiffMs;
::SetLastError(nOSError);
return bRes;
}
BOOL ConvertLocalTimeToUTCTime(SYSTEMTIME* pSt_Local, SYSTEMTIME* pOutSt_UTC)
{
//Convert local date/time from 'pSt_Local'
//'pOutSt_UTC' = if not NULL, receives converted UTC time
//RETURN:
// = TRUE if success
// = FALSE if error (check GetLastError() for info)
BOOL bRes = FALSE;
SYSTEMTIME stUTC = {0};
int nOSError = NO_ERROR;
if(pSt_Local)
{
//First get time zone info
TIME_ZONE_INFORMATION tzi;
if(GetDSTInfoForYear(pSt_Local->wYear, &tzi) != DST_ERROR)
{
if(::TzSpecificLocalTimeToSystemTime(&tzi, pSt_Local, &stUTC))
{
//Done
bRes = TRUE;
}
else
nOSError = ::GetLastError();
}
else
nOSError = ::GetLastError();
}
else
nOSError = ERROR_INVALID_PARAMETER;
if(pOutSt_UTC)
*pOutSt_UTC = stUTC;
::SetLastError(nOSError);
return bRes;
}
DST_STATUS GetDSTInfoForYear(USHORT uYear, TIME_ZONE_INFORMATION* pTZI)
{
//Get DST info for specific 'uYear'
//INFO: Year is not used on the OS prior to Vista SP1
//'pTZI' = if not NULL, will receive the DST data currently set for the time zone for the year
//RETURN:
// = Current DST status, or an error
// If error (check GetLastError() for info)
DST_STATUS tzStat = DST_ERROR;
int nOSError = NO_ERROR;
//Define newer APIs
DWORD (WINAPI *pfnGetDynamicTimeZoneInformation)(PDYNAMIC_TIME_ZONE_INFORMATION);
BOOL (WINAPI *pfnGetTimeZoneInformationForYear)(USHORT, PDYNAMIC_TIME_ZONE_INFORMATION, LPTIME_ZONE_INFORMATION);
//Load APIs dynamically (in case of Windows XP)
HMODULE hKernel32 = ::GetModuleHandle(L"Kernel32.dll");
ASSERT(hKernel32);
(FARPROC&)pfnGetDynamicTimeZoneInformation = ::GetProcAddress(hKernel32, "GetDynamicTimeZoneInformation");
(FARPROC&)pfnGetTimeZoneInformationForYear = ::GetProcAddress(hKernel32, "GetTimeZoneInformationForYear");
TIME_ZONE_INFORMATION tzi = {0};
//Use newer API if possible
if(pfnGetDynamicTimeZoneInformation &&
pfnGetTimeZoneInformationForYear)
{
//Use new API for dynamic time zone
DYNAMIC_TIME_ZONE_INFORMATION dtzi = {0};
tzStat = (DST_STATUS)pfnGetDynamicTimeZoneInformation(&dtzi);
if(tzStat == DST_ERROR)
{
//Failed -- try old method
goto lbl_fallback_method;
}
//Get TZ info for a year
if(!pfnGetTimeZoneInformationForYear(uYear, &dtzi, &tzi))
{
//Failed -- try old method
goto lbl_fallback_method;
}
}
else
{
lbl_fallback_method:
//Older API (also used as a fall-back method)
tzStat = (DST_STATUS)GetTimeZoneInformation(&tzi);
if(tzStat == DST_ERROR)
nOSError = ::GetLastError();
else
nOSError = ERROR_NOT_SUPPORTED;
}
if(pTZI)
{
*pTZI = tzi;
}
::SetLastError(nOSError);
return tzStat;
}
Bit of a c++ newbie so here we go;
I have a method that is parsing a date/time, however that date/time is passed to me always with 00:00:00 as the hh:mm:ss. As such i want to add in the values of the current systime in place of those values. I have methods that do this, and the first method is returning the correct time in UTC format.
bool CTRHTranslationRTNS::ParseDateSysTime(const char* pszString, time_t& tValue)
{
ASSERT(pszString != NULL);
// DateTime fields.
enum { YEAR, MONTH, DAY, HOURS, MINS, SECS, NUM_FIELDS };
CStringArray astrFields;
// Split the string into the date and time fields.
int nFields = CStringParser::Split(pszString, "- :T", astrFields);
// Not DD/MM/YYYY HH:MM:SS format.
if (nFields != NUM_FIELDS)
return false;
int anFields[NUM_FIELDS] = { 0 };
// Parse field numbers.
for (int i = 0; i < NUM_FIELDS; ++i)
anFields[i] = atoi(astrFields[i]);
tm oTime = { 0 };
//Add System Time instead
time_t sysyemTimeNow;
struct tm * ptm;
time ( &sysyemTimeNow );
ptm = gmtime ( &sysyemTimeNow );
// Copy fields to time struct.
oTime.tm_mday = anFields[DAY];
oTime.tm_mon = anFields[MONTH] - 1;
oTime.tm_year = anFields[YEAR] - 1900;
oTime.tm_hour = ptm->tm_hour;
oTime.tm_min = ptm->tm_min;
oTime.tm_sec = ptm->tm_sec;
oTime.tm_isdst = -1;
// Convert to time_t.
tValue = mktime(&oTime);
// Invalid field values.
if (tValue < 0)
return false;
return true;
}
In the second method I do some formatting on the date/time and this results in 2 hours being removed from the time.
string CTRHTranslationRTNS::ConvertDateSysTimeToDateInUTC(const string& bossDate)
{
time_t dealDate;
if (ParseDateSysTime(bossDate.c_str(), dealDate))
{
struct tm * ptm = gmtime(&dealDate);
char buffer [80];
strftime(buffer,80,"%Y-%m-%d %H:%M:%S",ptm);
return string(buffer);
}
else
{
throw exception(string("Invalid date/SysTime value: ").append(bossDate).c_str());
}
}
Just to be clear, the ParseDateSysTime method returns the time with the correct UTC value of 11:53, but as soon as
struct tm * ptm = gmtime(&dealDate);
is called the time changes to 08:53. It suggests this is a product of calling the gmtime() method but i am not sure.
Many Thanks
Graham
The reson is the mktime() method used in the first function uses local time, but gmtime() uses UTC time.
See http://www.cplusplus.com/reference/clibrary/ctime/mktime/ and http://www.cplusplus.com/reference/clibrary/ctime/gmtime/ for further explanation.
Try this function:
CTime Time2UTC(CTime original)
{
CString Formatted = original.FormatGmt(L"%Y%m%d%H%M%S");
int Year, Month, Day, Hour, Minute;
if (Formatted != L"" && Formatted.GetLength() >= 12)
{
Year = _wtol(Formatted.Left(4));
Month = _wtol(Formatted.Mid(4, 2));
Day = _wtol(Formatted.Mid(6,2));
Hour = _wtol(Formatted.Mid(8, 2));
Minute = _wtol(Formatted.Mid(10, 2));
CTime result(Year, Month, Day, Hour, Minute, 0);
return result;
}
else
return (CTime)NULL;
}