Weird characters at the beginning of a LPTSTR? C++

Question

I am using this code to get the windows version:

#define BUFSIZE 256

bool config::GetOS(LPTSTR OSv)
{
   OSVERSIONINFOEX osve;
   BOOL bOsVersionInfoEx;

   ZeroMemory(&osve, sizeof(OSVERSIONINFOEX));

   osve.dwOSVersionInfoSize = sizeof(OSVERSIONINFOEX);

   if( !(bOsVersionInfoEx = GetVersionEx ((OSVERSIONINFO *) &osve)) )
      return false;

   TCHAR buf[BUFSIZE];
   StringCchPrintf(buf, BUFSIZE, TEXT("%u.%u.%u.%u"), 
        osve.dwPlatformId,
            osve.dwMajorVersion,
            osve.dwMinorVersion,
            osve.dwBuildNumber);

   StringCchCat(OSv, BUFSIZE, buf);

   return true;
}

And I am testing it with:

LPTSTR OSv= new TCHAR[BUFSIZE];
config c;
c.GetOS(OSv);
MessageBox(OSv, 0, 0);

And in the msgbox I get something like this äì5.1.20 (where 5.1.20 is = to OSv) but the first 2 or 3 chars are some weird characters that I don't know when they came from. Even stranger, if I call that second piece again it shows it ok, it only show the weird characters the first time I execute it.

Does someone has an idea what's going on here?

Answer 1

LPTSTR OSv= new TCHAR[BUFSIZE];. <-- You've not initialized the memory block. It's filled with random garbage.

You tagged your question C++ -- is there any reason you're not using a std::vector<wchar_t> or std::wstring here instead of manually managing memory?

std::wstring config::GetOS()
{
   OSVERSIONINFOEX osve;
   BOOL bOsVersionInfoEx;

   ZeroMemory(&osve, sizeof(OSVERSIONINFOEX));

   osve.dwOSVersionInfoSize = sizeof(OSVERSIONINFOEX);

   if( !(bOsVersionInfoEx = GetVersionEx ((OSVERSIONINFO *) &osve)) )
      return L"ERROR"; //Actually the right thing to do here is throw an exception
                       //but I could see how that could be a problem for some code

   std::wstringstream formatter;
   formatter << osve.dwPlatformId << L'.'
             << osve.dwMajorVersion << L'.'
             << osve.dwMinorVersion << L'.'
             << osve.dwBuildNumber;
   return formatter.str();
}

Answer 2

Your problem is that you should be using StringCchCopy and not StringCchCat.

StringCchCat will search until it finds a 0 in the string, and then append the result there. Since you are not initializing your output string buffer to 0's, you cannot assume it will start with a 0.