convert Windows SYSTEMTIME to a string or char buf in C++ with user's "Region and Language" format?

Question

How does my C++ program convert a SYSTEMTIME in the user's preferred "long date format" either as defaulted from their Language setting, or as custom-set on the Control Panel->Region and Language dialog?

If it matters I'm on Visual Studio 2017 and primarily looking for C/C++03 type solutions but if there's a solution for newer C++ I wouldn't mind seeing it.

Answer 1

TCHAR buf[200];
GetDateFormat(LOCALE_USER_DEFAULT, DATE_LONGDATE, &mysystime, NULL, buf, 200);

Call GetTimeFormat as well if you also need the time part.

Answer 2

TIME_ZONE_INFORMATION tzi;
if ( GetTimeZoneInformation( &tzi ) == TIME_ZONE_ID_INVALID )
MyErrorFunction( "GetTimeZoneInformation() = TIME_ZONE_ID_INVALID : %s",
    GetLastErrorAsString().c_str() );
  :
  :

SYSTEMTIME st, stLocal;
BOOL bRV = FileTimeToSystemTime( ftLastAccessTime, &st );
SystemTimeToTzSpecificLocalTime( &tzi, &st, &stLocal );

GetDateFormat( LOCALE_USER_DEFAULT, DATE_LONGDATE, &stLocal,
               NULL, szBuf, sizeof( szBuf ) );

int iBufUsed = strlen( szBuf );
if ( iBufUsed < sizeof( szBuf ) - 2 )
     szBuf[ iBufUsed++ ] = ' ';

GetTimeFormat( LOCALE_USER_DEFAULT, 0, &stLocal,
               NULL, szBuf + iBufUsed, sizeof( szBuf ) - iBufUsed );

// szBuf holds Date and Time, in the user's timezone, formatted as the user prefers.