discuss.visual-prolog.com

Posted: **19 Aug 2023 21:16**

Hi, I am using this code from Visual C++, LoadLibrary does load the library well, GetProcAddress finds the function inside the DLL, but when I call to the pointer-to-function, the application crashes.

What am I doing wrong? Typedef declaration maybe? Is there any similar working sample for Visual C++?

Here is the code:

Code: Select all

typedef void (__stdcall * LPFNEXPORTEDPREDICATE)(void);
 
void CMFCApplication3View::OnBnClickedLoadPrologDll()
{
        HMODULE hMod = 0x0000;
        wchar_t wszDLLPath[256];
        char szFunctionName[100];
        LPFNEXPORTEDPREDICATE lpfnExportedPredicate = NULL;
 
        memset(wszDLLPath, 0, sizeof(wszDLLPath));
        wcscpy(wszDLLPath, _T("libProlog.dll"));
        strcpy(szFunctionName, "exportedPredicate");
        hMod = LoadLibrary(wszDLLPath);
        if (hMod)
        {
                lpfnExportedPredicate = (LPFNEXPORTEDPREDICATE)GetProcAddress(hMod, (LPCSTR)szFunctionName);
                if (lpfnExportedPredicate)
                {
                        lpfnExportedPredicate(); //Crashes here
                }
                FreeLibrary(hMod);
        }
}

Posted: **21 Aug 2023 21:24**

In that case the Visual Prolog predicate should be declared with 'language stdcall':

Code: Select all

class something
 
predicates
    exportedPredicate : () language stdcall.
...

Posted: **23 Aug 2023 23:01**

I have changed the export.cl file with stdcall, but now the GetProcAddress function stopped working from the client side. Cannot find "exportedPredicate" entry point.
It seems like there is a kind of "decorated names" aka "mangling" maybe using the class name as a prefix.

The export.cl file is as follows:

Code: Select all

class export
    
predicates
    exportedPredicate : () language stdcall.
 
end class export

I have supressed also the "open core" line.

From the C language caller (client part) I have tried GetProcAddress with function names like "export.exportedPredicate" and export::exportedPredicate" but without success.

My question is: Which is the right function name that I have to search for?

Thanks.

Posted: **23 Aug 2023 23:19**

I've found the way: I opened the binary file of the DLL and browsed for "exportedPredicate and found the real name as "?exportedPredicate@export@@SGXXZ"

The source code now works and it is like this:

Code: Select all

void CMFCApplication3View::OnBnClickedLoadPrologDll()
{
        HMODULE hMod = 0x0000;
        wchar_t wszDLLPath[256];
        char szFunctionName[100];
        LPFNEXPORTEDPREDICATE lpfnExportedPredicate = NULL;
 
        memset(wszDLLPath, 0, sizeof(wszDLLPath));
        wcscpy(wszDLLPath, _T("libTestProlog.dll"));
        strcpy(szFunctionName, "?exportedPredicate@export@@SGXXZ");
        hMod = LoadLibrary(wszDLLPath);
        if (hMod)
        {
                lpfnExportedPredicate = (LPFNEXPORTEDPREDICATE)GetProcAddress(hMod, (LPCSTR)szFunctionName);
                if (lpfnExportedPredicate)
                {
                        lpfnExportedPredicate();
                }
                FreeLibrary(hMod);
        }
}

Is there any way to use the equivalent of extern "C" to avoid the mangling

Posted: **24 Aug 2023 14:51**

Something as useful (forgot it before):

Code: Select all

class export
    
predicates
    exportedPredicate : () language stdcall as "exportedPredicate". 
 
end class export

Posted: **24 Aug 2023 19:59**

Great. Now it works perfectly!

Is there any documentation somewhere to specify prototypes of pointer-to-function to pass string, integer, float parameters from C to Prolog DLL?

Thank you very much!

Posted: **25 Aug 2023 7:11**

Have a look at Foreign Language Code and DLL Memory Handling.

Posted: **26 Aug 2023 17:55**

Really cool.
Thank you very much, Mr Puls!

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