Unable to find an entry point when calling C++ dll in C#

c#, c++, pinvoke

Solution

You need to use `extern "C"` when you export your function so that you suppress C++ name mangling. And you also should not try to p/invoke to members of a class. Use free functions instead:

extern "C" {
    __declspec(dllexport) int GiveMeNumber(int i)
    {
        return i;
    }
}

On the managed side your `DllImport` attribute is all wrong. Don't use `SetLastError` which is for Win32 APIs only. Don't bother setting `CharSet` if there are not text parameters. No need for `ExactSpelling`. And the calling convention is presumably `Cdecl`.

[DllImport("KingFuncDll.dll", CallingConvention=CallingConvention.Cdecl)]
public static extern int GiveMeNumber(int i);

Problem

I am trying to learn P/Invoke, so I created a simple dll in C++ KingFucs.h: ``` namespace KingFuncs { class KingFuncs { public: static __declspec(dllexport) int GiveMeNumber(int i); }; } ``` KingFuns.cpp: ``` #include "KingFuncs.h" #include <stdexcept> using namespace std; namespace KingFuncs { int KingFuncs::GiveMeNumber(int i) { return i; } } ``` So it does compile, then I copied this dll into my WPF's debug folder, with code: ``` [DllImport("KingFuncDll.dll", EntryPoint = "GiveMeNumber", SetLastError = true, CharSet = CharSet.Ansi, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)] public static extern int GiveMeNumber( int i ); ``` And calling it in button click: ``` private void Button_Click(object sender, RoutedEventArgs e) { int num = GiveMeNumber(123); } ``` But it gives me exception: Unable to find an entry point named 'GiveMeNumber' in DLL 'KingFuncDll.dll'. Really.... what have I done wrong... It obviously able to find the DLL, otherwise would be another exception. But my method name is exactly the same.... I can't think of other reason.

Original source

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