Calling a C++ .dll from C# throws a runtime error

Question

The following line is generating a runtime error in a C# GUI:

int x = myclass.number_from_dll();

I'm using Microsoft Visual Studio 2008.

The code in C# is:

class myclass { [DllImport("strat_gr_dll.dll", EntryPoint = "number_from_dll")] public static extern int number_from_dll(); }

The code in the C++ .dll is:

// This is an example of an exported function. DLL int number_from_dll(void) { return 42; }

The runtime error from .NET is:

An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)

Do you export that function with a friendly name?

Victor Hurdugaci
– Victor Hurdugaci

2010-08-02 19:13:16 +00:00
Commented Aug 2, 2010 at 19:13 — Victor Hurdugaci
– Victor Hurdugaci, Commented Aug 2, 2010 at 19:13

Hans Passant · Accepted Answer · 2010-08-02 19:15:31Z

Project + Properties, Build tab, Platform Target = x86.

Your C/C++ DLL was compiled in 32-bit mode. But your C# program is running on a 64-bit version of Windows and will run in 64-bit mode. That mix don't match. Creating a 64-bit version of you DLL is another solution. Build + Configuration Manager, Platform combo, New, x64.

Thank you soooooo much - I just spent the last 4 hours trying to track down this problem, you're a legend!

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