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POVB6 dll call to win32 C function
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  1. POVB6 dll call to win32 C function
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    copied!<p>I need to write some functions in C for someone else's VB6 project (that being outdated is beyond the scope of this question).</p> <p>During initial tests, I could not get the calls to work. I have supplied a .def file, I tried to use __declspec(dllexport), stdcall and WINAPI calling conventions. Each call I get an error message in VB6 saying "bad dll calling convention."</p> <p>Win32 C function prototypes:</p> <pre><code>long WINAPI BitmapFile_Open(char *pszFileName); void WINAPI BitmapFile_Close(long bmf); </code></pre> <p>note in the above I have tried several other calling conventions, including __declspec(dllexport) and stdcall, and neither work.</p> <p>Def file:</p> <pre><code>LIBRARY ImageLib EXPORTS BitmapFile_Open @1 BitmapFile_Open @2 </code></pre> <p>VB Global Module:</p> <pre><code> Declare Function BitmapFile_Open Lib "ImageLib.dll" (ByVal fileName As String) As Long Declare Function BitmapFile_Close Lib "ImageLib.dll" (ByVal bmFile As Long) </code></pre> <p>VB Code:</p> <pre><code>Dim myFile As Long myFile = BitmapFile_Open("test.bmp") BitmapFile_Close (myFile) </code></pre> <p>Also note that in the original functions, the bmFile is actually an address (pointer to a structure) but in VB it will be represented as long. However, since VB6 doesn't support pointers, I am casting from long in the C code. I hope you can understand what I'm trying to get at here. It has nothing to do with the error that is occurring. Any help is appreciated.</p> <p>Edit: I have used a dependency walker to determine that the functions are indeed being exported. VB6 is just not calling them without error.</p>
 

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