calling function in dll not working

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:

Code:

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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);

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This is the relevant code in my dll

Code:

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extern int testfunc ( int x );


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

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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.

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

Quote:

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Code:

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

---

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Quote:

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Originally Posted by Igor Vartanov

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

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

Code:

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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

Code:

---

extern int testfunc ( int x );

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

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

Quote:

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Originally Posted by Igor Vartanov

Besides the name mangling issue...

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Quote:

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extern int testfunc ( int x );

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

Quote:

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

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@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

Code:

---

#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

Code:

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#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;
}

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Try:

Code:

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extern "C" int testfunc ( int x );

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Viggy

Quote:

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Originally Posted by MrViggy

Try:

Code:

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extern "C" int testfunc ( int x );

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Viggy

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Nope, didn't work either :(

Quote:

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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.

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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. :D

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

Code:

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

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Quote:

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Originally Posted by Igor Vartanov

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. :D

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

Code:

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

---

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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..?

I believe it needs to be:

Loader:

Code:

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typedef int (__stdcall * voidFunc)(int);

---

DLL:

Code:

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

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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.

Quote:

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Originally Posted by vivendi

Nope, didn't work either :(

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

Quote:

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Originally Posted by Night_Wulfe

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

Code:

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extern "C" int __stdcall testfunc(int x)

---

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

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?

A lib file would be easier, but in my case i really need a dll.
When i used dumpbin on my dll it gave me the following output:

dumpbin \EXPORTS path\to\file.dll
File Type: DLL

Summary

1000 .data
1000 .idata
2000 .rdata
1000 .reloc
1000 .rsrc
4000 .text
10000 .textbss

Got it fixed. I had to use declspec(export). This is how it looks right now:

Code:

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extern "C" __declspec(dllexport) int testfunc ( int x );

..
..

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

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Thanks alot guys for your help!

Quote:

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A lib file would be easier, but in my case i really need a dll.

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You know, when you build a dll with export, the lib file is created as well. The one is called DLL's import library. Just search around for simple dll samples. :)