Hi, I have a C++ dll that I created myself. It has a function exported like so: __declspec(dllexport) int WINAPI StartServer() Now I can call this function from another C++ test application by doing the following: __declspec(dllimport) int WINAPI StartServer(); Then just call the function StartServer(). My question is how do I call this same function using a Visual C# application? I have tried adding it as a reference but VisualStudio wont allow me. I have also tried the following: using System.Runtime.InteropServices; public partial class Form1 : Form { const string _dllLocation = "ServerDLL.dll"; [DllImport(_dllLocation)] static extern int StartServer(); private void button1_Click(object sender, EventArgs e) { StartServer(); <- ERROR HERE } } if("undefined"!==typeof hljs)hljs._ha();else if("undefined"===typeof hljsLoading){hljsLoading=1;var a=document.getElementsByTagName("head")[0],e=document.createElement("link");e.type="text/css";e.rel="stylesheet";e.href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.7.0/styles/default.min.css";a.appendChild(e);e=document.createElement("script");e.type="text/javascript";e.onload=function(){var d={},f=0;hljs._hb=function(b){b.removeAttribute("data-hljs");var c=b.innerHTML;c in d?b.innerHTML=d[c]:(7 But when I come to the StartServer() in the button1_Click function I get the following error: DLLNotfoundexception Unable to load DLL 'ServerDLL.dll' The specified module could not be found..... What am I doing wrong here?? Thank for your help.

Master It may be that the name of the function has been 'mangled' which is common with C++ dlls. You could check the exported name using dumpbin or dependency walker or, alternatively, you can use the ordinal number of the function instead. If there's only one function in the dll, the ordinal should be #1, so you'd need to change the DllImport attribute to: [DllImport(_dllLocation, EntryPoint = "#1")] static extern int StartServer(); if("undefined"!==typeof hljs)hljs._ha();else if("undefined"===typeof hljsLoading){hljsLoading=1;var a=document.getElementsByTagName("head")[0],e=document.createElement("link");e.type="text/css";e.rel="stylesheet";e.href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.7.0/styles/default.min.css";a.appendChild(e);e=document.createElement("script");e.type="text/javascript";e.onload=function(){var d={},f=0;hljs._hb=function(b){b.removeAttribute("data-hljs");var c=b.innerHTML;c in d?b.innerHTML=d[c]:(7

Call a native C++ dll from C# WinApp

Master

Hi,
I have a C++ dll that I created myself.
It has a function exported like so:
__declspec(dllexport) int WINAPI StartServer()

Now I can call this function from another C++ test application by doing the following:
__declspec(dllimport) int WINAPI StartServer();

Then just call the function StartServer().

My question is how do I call this same function using a Visual C# application? I have tried adding it as a reference but VisualStudio wont allow me.

I have also tried the following:

using System.Runtime.InteropServices;

public partial class Form1 : Form
{
       const string _dllLocation = "ServerDLL.dll";
       [DllImport(_dllLocation)]

       static extern int StartServer();

       private void button1_Click(object sender, EventArgs e)
       {
              StartServer(); <- ERROR HERE
       }
}

But when I come to the StartServer() in the button1_Click function I get the following error:

DLLNotfoundexception
Unable to load DLL 'ServerDLL.dll' The specified module could not be found.....

What am I doing wrong here??

Thank for your help.

Zsigmond

Master The path of the dll is not found, specify the path of the dll file like
const string dllLocation ="C:\...\bin\ServerDLL.dll"_;

Master

Zsigmond thanks for the reply. I have tried this also but I still get the same error??

Could there be anything else the problem??

Thanks again.

Keith

Master It may not be ServerDll.dll that can't be found but some other (non-system) dll on which it depends.

If there is a dependency (you can check with Dependency Walker, if you're not sure), it might be an idea to copy both it and ServerDll to the same folder as your C# exe.

Master

Keith Yes you are correct, I needed to copy in the libmySQL.dll in to my exes directory.
But now I get a different error at the same place:
"Unable to find an entry point named 'StartServer' in DLL 'ServerDLL.dll'
Do you know what could be wrong here??
Thanks again for your help.

Keith

Master It may be that the name of the function has been 'mangled' which is common with C++ dlls.
You could check the exported name using dumpbin or dependency walker or, alternatively, you can use the ordinal number of the function instead.

If there's only one function in the dll, the ordinal should be #1, so you'd need to change the DllImport attribute to:

[DllImport(_dllLocation, EntryPoint = "#1")]
static extern int StartServer();

Master

Keith This has fixed my problem, excellent.
Many thanks for your help!