Perfect importing code not operating...

This code fails, and I have no idea why, it's been really bugging me, PLEASE HELP!!

main.cpp

Code:

---

#include <windows.h>
 
typedef int (WINAPI *CommProt)(int);
#define ReportError(x) MessageBox(0, TEXT(x), TEXT("Error"), MB_OK | MB_ICONERROR);

int WinMain(HINSTANCE hInst, HINSTANCE hPrevInst, LPSTR lpCmdLine, int nShow)
{
  HMODULE hDLL = LoadLibrary("appext.dll");
  if(hDLL == NULL)
      ReportError("Load of DLL failed.");
  CommProt CommFunc = (CommProt)GetProcAddress(hDLL,"Comm"));
  // This is where the error happens, the GetProcAddress() call fails.
  if(CommFunc == NULL)
      ReportError("Capture of function failed.");
  Comm(5); // This is where the program crashes.
  FreeLibrary(hDLL);
  hDLL = NULL;
  return 0;
}

---

appext.cpp

Code:

---

#include <windows.h>
 
int Comm(int nVar)
{
  char szDom[MAX_PATH];
  wsprintf(szDom, TEXT("Comm var &#37;d."), nVar);
  MessageBox(0, szDom, TEXT("Comm"), MB_OK | MB_ICONINFORMATION);
  return 0;
}
 
BOOL APIENTRY DllMain(HANDLE hMod, DWORD ulCall, LPVOID lpRes)
{
  return TRUE;
}

---

-Quaytrix

1. Dumping the code here and telling us it fails is stupid. We know it fails because you wouldn't be here asking for help otherwise. Try to give a little more information. At least you told us where the problem seems to be and what is occurring.
2. You are not checking if the DLL was properly loaded. It could be failing to load.
3. You are not checking if the function's location in said DLL was found. It could be failing to find such a function, especially since you define it as:
   
   
   Code:

   ---

   int Comm(int nVar);

   ---

   But you are declaring your function pointer to be of type:
   
   
   Code:

   ---

   int (WINAPI *CommProt)(int)

   ---

   Do you know the difference between C's default calling convention and the WINAPI? Do you know what happens if you mix them up?

That's for starters.

> char sz[MAX_PATH];
> wsprintf(sz, "Comm var %d.", nVar);
> MessageBox(0, sz, "Comm()", MB_OK | MB_ICONINFORMATION);
Use the TCHAR and TEXT macros to ensure UNCODE consistency throughout your code.

Okay, I have provided all the info I can think would be usefull. The program does get the dll sucessfuly, but can't capture the function.

And I used the macro where I have written text now too.

is it possible that the function is not being found because you are not using the correct calling conventions?

http://msdn2.microsoft.com/en-us/lib...z2(VS.71).aspx

Which goes back to point 3 of what I said..... :)

Does the DLL contain C++ code? Then you have to contend with name-mangling issues.

Yep, it's C++ code, and it's almost surely a name mangling issue. You should provide a .def file for the library.

Okay, I fixed the function and is using dllexport now too, but it still isn't working. I'm wondering if this isn't a compilation problem, does it compile and run fine for you?
main.cpp

Code:

---

#include <windows.h>

typedef __declspec(dllexport) int (WINAPI *CommProt)(int);
#define ReportError(x) MessageBox(0, TEXT(x), TEXT("Error"), MB_OK | MB_ICONERROR);

int WinMain(HINSTANCE hInst, HINSTANCE hPrevInst, LPSTR lpCmdLine, int nShow)
{
  HMODULE hDLL = LoadLibrary("appext.dll");
  if(hDLL == NULL)
      ReportError("Load of DLL failed.");
  CommProt CommFunc = (CommProt)GetProcAddress(hDLL,"Comm"));
  // This is where the error happens, the GetProcAddress() call fails.
  if(CommFunc == NULL)
      ReportError("Capture of function failed.");
  Comm(5); // This is where the program crashes.
  FreeLibrary(hDLL);
  hDLL = NULL;
  return 0;
}

---

appext.cpp

Code:

---

#include <windows.h>

__declspec(dllexport) int WINAPI Comm(int nVar)
{
  char szDom[MAX_PATH];
  wsprintf(szDom, TEXT("Comm var &#37;d."), nVar);
  MessageBox(0, szDom, TEXT("Comm"), MB_OK | MB_ICONINFORMATION);
  return 0;
}
 
BOOL APIENTRY DllMain(HANDLE hMod, DWORD ulCall, LPVOID lpRes)
{
  return TRUE;
}

---

-Quaytrix

Have you written a .def file yet?

dumpbin <dllname> /EXPORTS

or some dllExplorer will show you the real names expoter by your dll (without def file)

I suppose it is something like "Comm@4"

Even more complicated. I expect it to be a C++ mangled name. Something like _Comm??i?z

if in the header the function declared as extern "C" it will not be...

But there is no header file.

>> Bee: Have you written a .def file yet?

No, the compiler does that for me.

>> vart: I suppose it is something like "Comm@4"
>> Bee: I expect it to be a C++ mangled name.

Does this mean that I can replace my string in GetProcAddress() with the one from the .def file, and then it'll work?

Quote:

---

Originally Posted by Queatrix

>> Bee: Have you written a .def file yet?

No, the compiler does that for me.

>> vart: I suppose it is something like "Comm@4"
>> Bee: I expect it to be a C++ mangled name.

Does this mean that I can replace my string in GetProcAddress() with the one from the .def file, and then it'll work?

---

Have you looked at the exports list of your dll? Easiest way to answer your own question I suppose

Quote:

---

Originally Posted by Queatrix

>> Bee: Have you written a .def file yet?

No, the compiler does that for me.

---

That's not the point. The compiler uses the mangled name of the function, and that's unusable for importing. Write a .def file and you can give your function a readable export name.

Yes, using the def file works! Thank you for your help.