Why am I getting a "Unable to find an entry point named 'SquareRoot' in DLL" message?

Question

I am having trouble calling a C++ function from dll in VB.net project. I have tried with the simple examples shown below

For C++ dll

#include <cmath>
extern "C" __declspec(dllexport) double SquareRoot(double value)
{
    return pow(value, 0.5);
}

I build the dll and copy it to the VB.net folder

For VB.net project

Module Module1
    <Runtime.InteropServices.DllImport("DLL_Test.dll")> _
    Private Function SquareRoot(ByVal value As Double) As Double

    End Function

    Sub Main()
        MsgBox(SquareRoot(2))
    End Sub

End Module

I keep getting Additional information: Unable to find an entry point named 'SquareRoot' in DLL 'DLL_Test.dll'. When I run dumpbin.exe on DLL_Test.dll I get the following

File Type: DLL

  Summary

        1000 .data
        1000 .idata
        2000 .rdata
        1000 .reloc
        1000 .rsrc
        4000 .text
       10000 .textbss

I am not sure what I am missing, any ideas? Thanks in advance.

Answer 1

Name mangling. extern "C" doesn't turn it off, it just changes the rules.

You also have a calling convention mismatch.

You can solve both at once via __stdcall keyword on the C++ function.