I need to write some functions in C for someone else's VB6 project (that being outdated is beyond the scope of this question).
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."
Win32 C function prototypes:
long WINAPI BitmapFile_Open(char *pszFileName);
void WINAPI BitmapFile_Close(long bmf);
note in the above I have tried several other calling conventions, including __declspec(dllexport) and stdcall, and neither work.
Def file:
LIBRARY ImageLib
EXPORTS
BitmapFile_Open @1
BitmapFile_Open @2
VB Global Module:
Declare Function BitmapFile_Open Lib "ImageLib.dll" (ByVal fileName As String) As Long
Declare Function BitmapFile_Close Lib "ImageLib.dll" (ByVal bmFile As Long)
VB Code:
Dim myFile As Long
myFile = BitmapFile_Open("test.bmp")
BitmapFile_Close (myFile)
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.
Edit: I have used a dependency walker to determine that the functions are indeed being exported. VB6 is just not calling them without error.