How do I call unmanaged C/C++ code from a C# ASP.NET webpage

Question

I have an ASP.NET website that uses C# and I'd like to call functions from an unmanaged C/C++ DLL. How do I do it?

Answer 1

1. create an unmanaged dll:

   extern "C" __declspec(dllexport) __cdecl int sum(int a,int b); ---->
   

2. create a namespace/class to DllImport the above DLL

   using System.Runtime.InteropServices;
   namespace ImportDLL
   {
   public class importdll
   {
   public importdll()
   {
   }
   
   DllImport("mysum.dll",
             EntryPoint="sum",
             ExactSpelling=false,
             CallingConvention = CallingConvention.Cdecl)]
   public extern int myfun(int a, int b);
   }
   }
   

3. create a aspx code behind

   using ImportDLL;
   namespace TEST
   {
    public int my_result;
    protected importdll imp = new importdll();
    my_result = imp.myfun(1,1);
   }
   

Answer 2

Check out P/Invoke.

Calling Win32 DLLs in C# with P/Invoke

If it's a COM dll, then you can use COM Interop

Answer 3

Just adding that pinvoke.net is a great wiki/resource for your Win32 needs.