C# program call C# dll

Question

I want to use a C# exe to dynamically load dll that build by C# or C++, the C++ dll part is done, but C# dll not yet done because exe can not find the method in C# dll.

here is my C# dll code that will build a CSharp.dll:

namespace NamespaceName
{
    public class ClassName
    {
        static public double MethodName(string input)
        {
            Console.WriteLine(input);
            Console.Read();
            return 0;
        }
    }
}

here is my C# exe code:

using System;
using System.Runtime.InteropServices;

namespace TestCall
{
    class Program
    {
        [DllImport("kernel32.dll", EntryPoint = "LoadLibrary")]
        static extern int LoadLibrary([MarshalAs(UnmanagedType.LPStr)] string lpLibFileName);
        [DllImport("kernel32.dll", EntryPoint = "GetProcAddress")]
        static extern IntPtr GetProcAddress(int hModule, [MarshalAs(UnmanagedType.LPStr)] string lpProcName);
        [DllImport("kernel32.dll", EntryPoint = "FreeLibrary")]
        static extern bool FreeLibrary(int hModule);

        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
        private delegate double MethodName(string a);

        static void Main(string[] arg)  //pass in string array
        {
            string DllName = "...Desktop//CSharp.dll";                 //would be like: string  DllName = ChooseWhatDllToCall();
            string FuncName = "NamespaceName@ClassName@MethodName";    //would be like: string FuncName = ChooseWhatFuncToUse();
            int hModule = LoadLibrary(DllName);
            if (hModule == 0)
                return;
            IntPtr intPtr;
            intPtr = GetProcAddress(hModule, FuncName);
            if ((int)intPtr == 0)
            {
                FreeLibrary(hModule);
                return;
            }
            MethodName run = (MethodName)Marshal.GetDelegateForFunctionPointer(intPtr, typeof(MethodName));
            string input = "just a string that will print by dll method";
            double result = run(input);
            FreeLibrary(hModule);
            return;
        }
    }
}

If I'm loading Cpp.dll, the if ((int)intPtr == 0) will be false, and loading CSharp.dll will be true, so I'm guessing I need to edit string FuncName = "NamespaceName@ClassName@MethodName"; to something else. How can I fix this?

If you want to load C# library from C# code - use methods appropriate for this (such as `Assembly.LoadFrom`). — Evk, Feb 27 '18 at 07:01
You probably want to .net reflection. I am lying in bed right now, so I can't do a nice link. But Google is good: .net reflection load library — Matthew, Feb 27 '18 at 07:08
If you want to use the same calling code for managed and unmanaged DLLs then you can use UnmanagedExports. — David Heffernan, Feb 27 '18 at 07:58

score 1 · Answer 1 · answered Feb 27 '18 at 09:27

I answer my own question now, it may not be perfect but it work, thanks for comment suggestion.

using System;
using System.Runtime.InteropServices;
using System.Reflection;

namespace TestCall   
{
    class Program
    {
        [DllImport("kernel32.dll", EntryPoint = "LoadLibrary")]
        static extern int LoadLibrary([MarshalAs(UnmanagedType.LPStr)] string lpLibFileName);
        [DllImport("kernel32.dll", EntryPoint = "GetProcAddress")]
        static extern IntPtr GetProcAddress(int hModule, [MarshalAs(UnmanagedType.LPStr)] string lpProcName);
        [DllImport("kernel32.dll", EntryPoint = "FreeLibrary")]
        static extern bool FreeLibrary(int hModule);
        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
        private delegate double MyMethod(string a);

        static void Main(string[] arg) 
        {

            string DllName = "...Desktop\\CSharp.dll";  //or Cpp.dll
            string FuncName = "MyMethod";


            string input = "Just A String";


            int hModule = LoadLibrary(DllName); // you can build it dynamically 
            IntPtr intPtr = GetProcAddress(hModule, FuncName);
            if ((int)intPtr!=0 && hModule != 0)  //can I try this way?
            {                                    //                      Yes!
                MyMethod run = (MyMethod)Marshal.GetDelegateForFunctionPointer(intPtr, typeof(MyMethod));
                double result = run(input);
                Console.WriteLine(result);
                Console.Read();
                FreeLibrary(hModule);
                return;
            }
            else                                 //No! 
            {
                FreeLibrary(hModule);

                                                 //so I try other way
                var DLL = Assembly.LoadFile(DllName);
                foreach (Type type in DLL.GetExportedTypes())
                {
                    var c = Activator.CreateInstance(type);
                    type.InvokeMember(FuncName, BindingFlags.InvokeMethod, null, c, new object[] { input });
                }
                return;
            }
        }
    }
}

C# program call C# dll

1 Answers1