How do I get a specific TIME_ZONE_INFORMATION struct in Win32? - winapi

Question

The Win32 GetTimeZoneInformation function returns your systems local time zone as set up in the control panel. How do I get another specific time zone? Is there a call that does this?
Tony

Answer 1

According to this the information for the different timezones is stored in the registry, so you will have to retrieve the information from there and populate the TIME_ZONE_INFORMATION struct yourself.
Quote from the msdn article
Remarks
Settings for each time zone are stored in the following registry key:
HKEY_LOCAL_MACHINE
SOFTWARE
Microsoft
Windows NT
CurrentVersion
Time Zones
time_zone_name

Answer 2

code:
#include <stdio.h>
#include <windows.h>
#define pWin32Error(dwSysErr, sMsg )
typedef struct _REG_TZI_FORMAT
{
LONG Bias;
LONG StandardBias;
LONG DaylightBias;
SYSTEMTIME StandardDate;
SYSTEMTIME DaylightDate;
} REG_TZI_FORMAT;
#define REG_TIME_ZONES "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Time Zones\\"
#define REG_TIME_ZONES_LEN (sizeof(REG_TIME_ZONES)-1)
#define REG_TZ_KEY_MAXLEN (REG_TIME_ZONES_LEN + (sizeof(((TIME_ZONE_INFORMATION*)0)->StandardName)/2) -1)
int GetTimeZoneInformationByName(TIME_ZONE_INFORMATION *ptzi, const char StandardName[]) {
int rc;
HKEY hkey_tz;
DWORD dw;
REG_TZI_FORMAT regtzi;
char tzsubkey[REG_TZ_KEY_MAXLEN+1] = REG_TIME_ZONES;
strncpy(tzsubkey + REG_TIME_ZONES_LEN, StandardName, sizeof(tzsubkey) - REG_TIME_ZONES_LEN);
if (tzsubkey[sizeof(tzsubkey)-1] != 0) {
fprintf(stderr, "timezone name too long\n");
return -1;
}
if (ERROR_SUCCESS != (dw = RegOpenKey(HKEY_LOCAL_MACHINE, tzsubkey, &hkey_tz))) {
fprintf(stderr, "failed to open: HKEY_LOCAL_MACHINE\\%s\n", tzsubkey);
pWin32Error(dw, "RegOpenKey() failed");
return -1;
}
rc = 0;
#define X(param, type, var) \
do if ((dw = sizeof(var)), (ERROR_SUCCESS != (dw = RegGetValueW(hkey_tz, NULL, param, type, NULL, &var, &dw)))) { \
fprintf(stderr, "failed to read: HKEY_LOCAL_MACHINE\\%s\\%S\n", tzsubkey, param); \
pWin32Error(dw, "RegGetValue() failed"); \
rc = -1; \
goto ennd; \
} while(0)
X(L"TZI", RRF_RT_REG_BINARY, regtzi);
X(L"Std", RRF_RT_REG_SZ, ptzi->StandardName);
X(L"Dlt", RRF_RT_REG_SZ, ptzi->DaylightName);
#undef X
ptzi->Bias = regtzi.Bias;
ptzi->DaylightBias = regtzi.DaylightBias;
ptzi->DaylightDate = regtzi.DaylightDate;
ptzi->StandardBias = regtzi.StandardBias;
ptzi->StandardDate = regtzi.StandardDate;
ennd:
RegCloseKey(hkey_tz);
return rc;
}
#define ZONE "Russian Standard Time"
int main(int argc, char* argv[])
{
DWORD dw;
TIME_ZONE_INFORMATION tzi;
dw = GetTimeZoneInformationByName(&tzi, ZONE);
if (dw != 0) return 1;
SYSTEMTIME lt;
SYSTEMTIME ut = {
2000, /*WORD wYear;*/
1, /*WORD wMonth;*/
0, /*WORD wDayOfWeek;*/
1, /*WORD wDay;*/
12, /*WORD wHour;*/
0, /*WORD wMinute;*/
0, /*WORD wSecond;*/
0 /*WORD wMilliseconds;*/
};
SystemTimeToTzSpecificLocalTime(&tzi, &ut, &lt);
printf("%d-%02d-%02d %02d:%02d:%02d UTC\n", ut.wYear, ut.wMonth, ut.wDay, ut.wHour, ut.wMinute, ut.wSecond);
printf("=\n");
printf("%d-%02d-%02d %02d:%02d:%02d Europe/Moscow\n", lt.wYear, lt.wMonth, lt.wDay, lt.wHour, lt.wMinute, lt.wSecond);
return 0;
}