Calling DLL fucn with ShortString param fails

• Previous message: Les Pawelczyk: "Re: Make a program unkillalbe"
• Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

Date: Wed, 31 Dec 2003 02:17:01 -0500

Hi,

I have a .DLL library providing me with a function which returns false
or true depending on some conditions. It's declared in DLL as:

//----------------------
extern "C" __declspec(dllexport) _stdcall bool VPNStart();
//----------------------

And i call it from an app (using func Start):

//----------------------
typedef bool (*HVPNSTART)(void);

bool Start()
{
   HINSTANCE hLib = LoadLibrary("MyDLL.DLL");
   if (hLib == NULL) {
     MessageBox(0, "Unable to Load MyDLL.DLL", "Error", MB_OK);
     return false;
   }
   HVPNSTART vs = (HVPNSTART)GetProcAddress(hLib, "VPNStart");
   if (vs == NULL) {
     MessageBox(0, "Failed calling VPNStart", "Error", MB_OK);
     FreeLibrary(hLib);
     return false;
   }
   bool result = vs();

   //MessageBox(0, "VPNStart Loaded!", "SUCCESS", MB_OK);
   if (result) MessageBox(0, "TRUE", "RESULT", MB_OK);
   else MessageBox(0, "FALSE", "RESULT", MB_OK);

   FreeLibrary(hLib);
   return result;
}
//----------------------

Everything works perfect until... i add an argument to the DLL fucn
VPNStart:
//----------------------
extern "C" __declspec(dllexport) _stdcall bool VPNStart();
//----------------------

So i change the main app code:
//----------------------
typedef bool (*HVPNSTART)(ShortString);
bool Start( ShortString s ) {...}

It starts to act WEIRD!!! When i trace (F8 -:)) thru the 'Start()' func
i see the following - after i load library, i write down it's address,
say ':013A000'.
But after the line 'result = vs(s)', the hLib address changes to
':8000004', and of course after i 'FreeLibrary' and return, it gives me
an access violation... How come the address of library handle could change?

I also tried to pass char* instead of ShortString, doesn't work also...

Any ideas, PLEASE!!!

Thank you,
Andrey

• Previous message: Les Pawelczyk: "Re: Make a program unkillalbe"
• Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]