C# (platform: Active (Any CPU) vs C++ (Win32) DLL ===>>> HRESULT 0x8007000B

Question

I called C++ DLL from C# application. C++ configuration is (x86, Win32) and C# configuration is (x86, Active (Any CPU). I've got HRESULT: 0x8007000B. The two configurations are as attached.

Answer 1

I talked with the author of the original C# application program and he mentioned that he linked some 64-bit DLLs which make the application run at 64-bit modes.
So, I tried another alternative: build both DLL & application into 64-bit ones and should not have conflict. It works.
The important is that even using dumpbin /headers to get the 32-bit headers, there is still some 64-bit codes embedded in it.

Answer 2

When calling c++ dll in c# code, you need to pay attention to CallingConvention.

The default in C++ is the cdecl calling convention, and the default in C# is the stdcall calling convention.

Therefore, please try to set the calling convention to cdecl in C#.

[DllImport("xx.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]  
public static extern int AddNumber(int a, int b);  

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Answer 3

Are you absolutely sure that the C++ DLL that is being used by the C# code is actually a 32-bit DLL?

If you mistakenly copied a 64-bit DLL to the folder that contains the C# executable that is the DLL that will be used since your example does not provide a path to the DLL in the DllImport statement. A subsequent build of a 32-bit DLL C++ project will not necessarily place the DLL output where C# will find it and so the wrong DLL (64-bit version) will be used.

You can verify the bitness of the C++ DLL being used by running dumpbin /headers on it. For examples of the output that show the bitness of a DLL -

32-bit DLL

64-bit DLL