calling function in dll not working

[vivendi]

I'm trying to call a function in a dll. I created this dll myself too. When i run my code i get am 'Exception unhandled' error. Can someone please tell me what i'm doing wrong?

In my exe file i basically do this:

typedef int (__stdcall * voidFunc)(int);


//in my main function
	dllEngine = LoadLibrary ( L"test_engine.dll" );

	if ( dllEngine == 0 )
		MessageBoxW ( NULL, L"failed loading DLL", L"ERROR", MB_OK );

	testfunc = (voidFunc)GetProcAddress ( dllEngine, "testfunc" );
	int x = testfunc(5);

This is the relevant code in my dll

extern int testfunc ( int x );


int testfunc (int x)
{
	MessageBoxW ( NULL, L"test", L"blaat", MB_OK );
	return x;
}

[hoxsiew]

Are you checking GetProcAddress's return? I'm guessing that without "extern C" your getting a very different name exported than the "testfunc" you're expecting.

[Igor Vartanov]

Besides the name mangling issue, ain't you see an inconsistency in the declarations?

typedef int (__stdcall * voidFunc)(int);
extern int testfunc ( int x );

[vivendi]

Besides the name mangling issue, ain't you see an inconsistency in the declarations?

I don't know how i got that mixed up, but i changed it. But it's still not working.

typedef int (* testfunc)(int);

//in my main function
	testfunc bla(0);
	dllEngine = LoadLibrary ( L"test_engine.dll" );

	if ( dllEngine == 0 )
		MessageBoxW ( NULL, L"failed loading DLL", L"ERROR", MB_OK );

	bla = (testfunc)GetProcAddress ( dllEngine, "testfunc" );
	int x = bla(5);

The DLL file

extern int testfunc ( int x );

int testfunc (int x)
{
	MessageBoxW ( NULL, L"test", L"blaat", MB_OK );
	return x;
}

[hoxsiew]

Are you sure "testfunc" exists in your dll? You're not checking the return from GetProcAddress()!

[Igor Vartanov]

Besides the name mangling issue...

extern int testfunc ( int x );

As far as I understand, you compile it as C++. So this must be the actual export name of your testfunc:

008 00000000 SECT3 notype () External | ?testfunc@@YAHH@Z (int __cdecl testfunc(int))

[vivendi]

@hoxsiew
The return value of GetProcAddress is 0x00000000. So for some reason it can't find it...

@Igor Vartanov
You mean that the function name in my dll should also have 'extern' infront of it? Anyway, i tried it but also didn't work.

I'll post everything i have so far. Perhaps you can see where i go wrong.

exe file

#include <windows.h>

typedef int (* testfunc)(int);
int WINAPI WinMain ( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow )
{
	MSG msg;
	HMODULE dllEngine;
	
	testfunc bla(0);

	dllEngine = LoadLibrary ( L"test_engine.dll" );

	if ( dllEngine == 0 )
		MessageBoxW ( NULL, L"failed loading DLL", L"ERROR", MB_OK );

	bla = (testfunc)GetProcAddress ( dllEngine, "testfunc" );
	int x = bla(5);

	while ( GetMessage ( &msg, NULL, 0, 0 ) > 0 )
	{
		TranslateMessage ( &msg );
		DispatchMessage ( &msg );
	}

	return msg.wParam;
}

DLL file

#include <windows.h>

extern int testfunc ( int x );
BOOL WINAPI DllMain ( HINSTANCE hInstance, DWORD fwdReason, LPVOID lpvReserved )
{
	switch(fwdReason)
	{
		case DLL_PROCESS_ATTACH:
			break;
		case DLL_THREAD_ATTACH:
			break;
		case DLL_PROCESS_DETACH:
			break;
		case DLL_THREAD_DETACH:
			break;
	}
	return(TRUE);
}

extern int testfunc (int x)
{
	MessageBoxW ( NULL, L"test", L"blaat", MB_OK );
	return x;
}

[MrViggy]

Try:

extern "C" int testfunc ( int x );

Viggy

[vivendi]

Try:

extern "C" int testfunc ( int x );

Viggy

Nope, didn't work either

[Igor Vartanov]

You mean that the function name in my dll should also have 'extern' infront of it? Anyway, i tried it but also didn't work.

Actually I meant you have to use the actual export name while finding the proc addess. This is what hoxiew told you about from the beginning: before resolving the function name to its address you make sure you use correct export name.

Export name may be not same to function name, in general case.

bla = (testfunc)GetProcAddress ( dllEngine, "?testfunc@@YAHH@Z" );

[vivendi]

Actually I meant you have to use the actual export name while finding the proc addess. This is what hoxiew told you about from the beginning: before resolving the function name to its address you make sure you use correct export name.

Export name is not same to function name, in general case.

bla = (testfunc)GetProcAddress ( dllEngine, "?testfunc@@YAHH@Z" );

I see what you mean, but that's how C++ export function names. But since i'm using extern "C" now i avoid that name mangling, right..?

[Night_Wulfe]

I believe it needs to be:

Loader:

typedef int (__stdcall * voidFunc)(int);

DLL:

extern "C" int __stdcall testfunc(int x)
{
    //...
}

If the function call isn't __stdcall, the name still gets mangled, even if you use extern "C". I remember this because I spent days trying to find the problem for the exact same reason.

[Igor Vartanov]

Nope, didn't work either

Say you've built your dll alright. What is the export name inside? Did you ever hear about dumpbin.exe? depends.exe?

[Igor Vartanov]

I believe it needs to be:
. . .
DLL:

extern "C" int __stdcall testfunc(int x)

This will produce _testfunc@4 export. So, it won't work, again.

[Igor Vartanov]

I wonder why LoadLibrary is used with such a persistence? Ain't it easier to just build a client with .lib file and forget about the name mangling nightmare?