Question

I need to open a html help file from within a legacy windows application written in old version of C++ Builder. HtmlHelp is loaded via HtmlHelp.ocx, which I am loading via LoadLibrary.

This has worked fine for years, but it does not work anymore in Windows 7 x64. It might also fail under Windows7 x86, but I don’t have any computer with this OS, so I can’t try it out at the moment.

I am loading hhctrl.ocx dynamically as follows:

#define HHPathRegKey "CLSID\\{adb880a6-d8ff-11cf-9377-00aa003b7a11}\\InprocServer32"

bool THTMLHelper::LoadHtmlHelp()
{
  HKEY HHKey;
  DWORD PathSize = 255;
  char Path[255];
  bool R = false;

  if (::RegOpenKeyExA(HKEY_CLASSES_ROOT, HHPathRegKey, 0, KEY_QUERY_VALUE, (void **)&HHKey) == ERROR_SUCCESS)
  {
    if (::RegQueryValueExA(HHKey, "", NULL, NULL, (LPBYTE)Path, &PathSize) == ERROR_SUCCESS)
    {
      //*****************************************
      //LOADING FAILS HERE
      //PATH IS %SystemRoot%\System32\hhctrl.ocx          
      //*****************************************
      HHLibrary = ::LoadLibrary(Path);
      if (HHLibrary != 0)
      {
        __HtmlHelp = (HTML_HELP_PROC) ::GetProcAddress(HHLibrary, "HtmlHelpA");
        R = (__HtmlHelp != NULL);
        if (!R)
        {
          ::FreeLibrary(HHLibrary);
          HHLibrary = 0;
        }
      }
    }
    ::RegCloseKey(HHKey);
  }
  return R;
}

I checked if %SystemRoot%\System32\hhctrl.ocx exists on the Windows 7 system and it does.

Why does loading it via LoadLibrary fail? How can I work around this problem?

EDIT: GetLastError says (in German, so I am just translating): “Could not find file.” But I debugged the function and the path is “%SystemRoot%\System32\hhctrl.ocx” and the file does exist.

Also, since two answers point in the direction of 64-bit vs 32-bit problems: My application is a 32 bit executable compiled in C++ Builder 5, so it should be a 32 bit process if I’m not mistaken. Or am I wrong to assume that?

Answer 1

Use ExpandEnvironmentStrings function to expand %SystemRoot%\System32\hhctrl.ocx to real path on user’s intallation. 64bit OS will redirect expanded path to 32bit dll correctly.