Thread: Dll Problem

Hi! I am aking my first DLL and I wrote a function to play a sound and then I wrote a VB app to call on the dll. When I run my App, it gets a run time error saying my DLL has a

"Bad Dll Calling Convention"

Here is my Dll code.

#include "stdafx.h"
#include <mmsystem.h>
extern "C" __declspec(dllexport) void PlayWav(char File);

BOOL APIENTRY DllMain( HANDLE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{

switch(ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
break;
case DLL_THREAD_ATTACH:
break;
case DLL_PROCESS_DETACH:
break;
case DLL_THREAD_DETACH:
break;
}

return TRUE;
}

void PlayWav(char File){
PlaySound(&File,NULL,SND_FILENAME|SND_ASYNC);
}


What am I doing wrong? Thanks!

I'm no expert with VB, but I understand that VB can only use the standard calling convention (__stdcall). While you are exporting your function using the C calling convention.

Try this (I think it's correct):

extern "C" void __declspec(dllexport) __stdcall PlayWav(char File);

Ok, I changed my code using a class as so

class PlayWav {
public:
PlayWav();
PlayWav(char File){
PlaySound(&File,NULL,SND_FILENAME|SND_ASYNC);
}
};

However, when my app runs it, I get another runtime error saying

"Can't Find Dll Entry Point PlayWav in DreamLib.Dll"

Argh..... What am I doing wrong? Thanks

>Ok, I changed my code using a class as so

Are you saying you now are trying to export C++ classes from a DLL to be used by a VB app? I don't recommend this as it's going to put you on stoney ground, unless you want to get into COM.

I don't wanna make a com file. I just wanna write a Dll function that can be executed my other programs calling on it. That's all I want. Any ideas? Thanks!

Then stick to flat functions using the standard calling convention.

So what do I need to change? What am I doing wrong?

// DreamLib.cpp : Defines the entry point for the DLL application.
//

#include "stdafx.h"
#include <mmsystem.h>


BOOL APIENTRY DllMain( HANDLE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{

switch(ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
break;
case DLL_THREAD_ATTACH:
break;
case DLL_PROCESS_DETACH:
break;
case DLL_THREAD_DETACH:
break;
}
return TRUE;

}

PlayWav(char File){
PlaySound(&File,NULL,SND_FILENAME|SND_ASYNC);
}

Include the prototype:

extern "C" void __declspec(dllexport) __stdcall PlayWav(char File);

and change your PlayWav definition to

Code:

void __stdcall PlayWav(char File)
{
...
}

There is stacks of info and examples on the web, if you search for it.

Finally, I assume you're using VC++ as your compiler. If not, you may run into name decoration problems with standard call.

Yes, I am using VC++.NET as my compiler and I just tried what you told me but I still got the same
"Can't Find Entry Point" runtime error. Any other ideas? Thanks so much!

Try defining your DllMain as:

BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fwdreason, LPVOID lpvReserved)

notice the WINAPI, rather APIENTRY

Beyond that, don't hink I can help. Find an example where someone has built a DLL in C/C++ for use with VB.

Edit : In fact, I think WINAPI is nothing more than a #define for __stdcall.

Hmmm... yeah that still doesn't work. Thanks though.

Wasn't WinMM.Dll written in C++... or Assembly? Or maybe both. Either way WinMM.Dll works with Vb. Thanks so much!!!!!!

Found these:

http://www.experts-exchange.com/Prog..._20192782.html

http://builder.com.com/article.jhtml...11218adm01.htm