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The nightmare of importing C# DLL to MQL5

Hy everyone i have a bit of a problem, I program mostly in python, and it's been a while actually since i coded in C# and i code in mql every now and again. My problem is i built a C# dll file that has a couple of simple functions:
[DllExport("debugger", CallingConvention = CallingConvention.StdCall)]
[return: MarshalAs(UnmanagedType.LPWStr)]
public static string debugger()
{
return "Send help!! SOS";
}
[DllExport("debugger2", CallingConvention = CallingConvention.StdCall)]
public static int debugger2()
{
return 12345;
}
This is my simple code from my C# file, it's all inside a public static class and the Solution platform is x64. Code compiles just fine and i find no issues. Now this is how my MetaEditor code looks:
#import "simpleFunctions.dll"
string debugger();
int debugger2();
#import
int OnInit()
{
//Print a statement just to show where code crashes
Print("We are definitly in it :D");
Print(debugger);
}
From what the Journal tells me everything runs just fine, the file is added from libraries and the print statement at the beginning of the OnInit function runs as well. The problem is come when calling the first debugger function from my dll file, just below my Print statement in the journal i get the following errors:
- Cannot find 'debugger', in 'simpleFunctions.dll'
- unresolved import function call
- OnInit critical error
- tester stopped because OnInit failed
I have searched all over the internet to my dissatisfaction of finding that no one really answers this question in a practical way. I suspect the error lies maybe in the C# side of things with regard to data type differences but i really don't know where to continue looking at this point. Any help would be greatly appreciated.

Well after searching probably every website for an answer relating to my question, switching back to python and trying a different way to connect to mql5 (using sockets), than finally trying C++ and spending the last two days learning that, I think I finally solved my problem. Only posting this to help anyone who might have a similar problem in the future. I figured that since MQL5 is more like C++ than C# the linking process would be a bit easier. The code it's self was not complex at all because I was just trying to get functions running in MQL5 from C++.
#include "pch.h"
#include "CPPMQLSQLConnector.h"
#define CPPMQLSQLCONNECTOR_API
#include <string>
std::string __stdcall myString(std::string Words)
{
static std::string myWords = "This is about to work I can feel it. ";
return myWords + Words;
}
int __stdcall myInt(int numbr)
{
static int myNumber = 1998;
numbr = 22;
return myNumber + numbr;
}
Note the __stdcall before method pointer, calling convention is required to let MQL5 know how to get the functions from the library.
In my C++ header file I let C++ know which functions I want to export using the '__declspec(dllexport)' and the '__declspec(dllimport)', my opinion on this issue is worth as much as you paid for it but my understanding is that the export keyword let's C++ know which functions I would like to export and the import keyword is used by MQL5 or which ever application, to know which functions to import. My header file
#pragma once
#include <string>
#ifndef MYDLL
#define MYDLL
#ifdef CPPMQLSQLCONNECTOR_API
extern "C" __declspec(dllexport) std::string __stdcall myString(std::string Words);
extern "C" __declspec(dllexport) int __stdcall myInt(int numbr);
#else
extern "C" __declspec(dllimport) std::string __stdcall myString(std::string Words);
extern "C" __declspec(dllimport) int __stdcall myInt(int numbr);
#endif
#endif
We use the extern "C" keyword to let the compiler know it should expect 'C' code.
Finally the MQL5 code, it's very simple. We just import the dll and and start using the functions for what ever purpose they were made
#import "CPPMQLSQLConnector.dll"
string myString(string s);
int myInt(int i);
#import
int OnInit()
{
string Word = "Momma I made it!!!!!!!!!!!!";
int numbr = 25;
Print("We definitely init ;D");
Print("La string: ", myString(Word));
Print("La integer: ", myInt(numbr));
return(INIT_SUCCEEDED);
}

C# code can't "find" exported function in a DLL, Works in C++ test program [duplicate]

This question already has answers here:
Unable to find an entry point when calling C++ dll in C#
(3 answers)
Closed 3 years ago.
I created a C++ (native) DLL that exports one function and I'm trying to call in from C# (managed) code and I receive runtime error that the function name can't be found in my DLL.
Here's the code of the DLL:
#include "pch.h"
#include "framework.h"
#include "Device.h"
// This is an example of an exported function.
DEVICE_API bool DeviceAvailable(void)
{
return false;
}
The header exports the function like:
#ifdef DEVICE_EXPORTS
#define DEVICE_API __declspec(dllexport)
#else
#define DEVICE_API __declspec(dllimport)
#endif
DEVICE_API bool DeviceAvailable(void);
In C# I import the function as such:
.. enclosing code ...
internal static class NativeMethods
{
[DllImport("Device.dll", CharSet = CharSet.Auto)]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool DeviceAvailable();
[DllImport("user32.dll", CharSet = CharSet.Auto)]
[return: MarshalAs(UnmanagedType.I4)]
public static extern int MessageBox(IntPtr hWnd, String text, String caption, uint type);
}
When I call NativeMethods.DeviceAvailable(), I get an error on invocation:
System.EntryPointNotFoundException
HResult=0x80131523
Message=Unable to find an entry point named 'DeviceAvailable' in DLL 'Device.dll'.
The MessageBox function works fine when called by the program (C#). A C++ test program is able to find and invoke the DLL function.

I guess your problem related to access settings on function level when creating the mentioned functions ic DLL.
here
you can find a useful links could help you to understand the case better and to find the best solution.

using cpp dll in c# code

I'm trying to use native c++ dll inside a c# application.
I followed this article to get started.
Its working fine while the dll using only c files (like in the tutorial), but when using cpp files I cant make it work.
using the dumpbin tool I can see that my exported function names changed.
for example a function call 'next' changed to '?next##YAHH#Z' and when I'm trying to call it in the c# code it cant find it.
my dll code is:
__declspec(dllexport)
int next(int n)
{
return n + 1;
}
the c# code
[DllImport("lib.dll", CallingConvention = CallingConvention.Cdecl)]
extern static int next(int n);
its the same code while using c file or cpp files
Thanks in advance
Amichai

What you are attempting to do is to make a trampoline function, to externalize the use of your C++ objects.
What you are experiencing is called symbol mangling. It is a c++-specific way of naming the symbols (like the functions) in a dynamic library and an executable, to enable polymorphism.
You have to specify that you want to cancel the mangling effect by using an extern "C" statement in your library code, just like this:
extern "C" __declspec(dllexport)
int next(int n)
{
return n + 1;
}
More on this here: Exporting functions from a DLL with dllexport

Please provide the Entry Point
An example below
[DllImport("lib.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "next", CharSet = CharSet.Ansi)]
static extern int next(int n);
Hopefully It helps.

How do I use a DLL function in C# without adding the DLL as reference?

I'm trying to use functions from a DLL that can't be added as Reference through Visual Studio (a message saying "reference cannot be added" appears). However, I've gotten instructions from the creator of the DLL and they suggested I use them like this in VB.Net:
Private Declare Function Prn_Init Lib "VAx_VPOS396_APPAPI.dll" () As Integer
That works, but now I want to write a program in C#. How do I "translate" that declaration to C#?
Additional: In C++ the declaration comes in a *.h file with these lines:
#ifndef _VPOS396DLL_API_H
#define _VPOS396DLL_API_H
VPOS396_DLL_API int Prn_Init(void);

You should create the method(s) you want to use in C#, make them extern and add a [DllImport] attribute. For example:
[DllImport("kernel32.dll")]
static extern bool Beep(uint dwFreq, uint dwDuration);
See https://msdn.microsoft.com/en-us/library/aa984739%28v=vs.71%29.aspx

[System.Runtime.InteropServices.DllImport("VAx_VPOS396_APPAPI.dll")]
public static extern unsafe Int32 Prn_Init(void);
("unsafe" is optional)

C++ function exported in dll and loaded from C#

I have in C++:
void __declspec(dllexport) foo(HWND wnd)
And in C#
[DllImport("MyDll.dll", CharSet = CharSet.Ansi)]
public static extern void foo(IntPtr wnd);
When I'm trying to call it I have this error - Additional information: Unable to find an entry point named 'foo' in DLL. I tried to inspect the dll and I have the function with the fallowing definition:
Undecorated C++ Function:
void cdecl foo(struct HWND *)
I searched on several forums and is seems that this is the right way to do this... Do you know why I have this run time error?

You need to disable C++ name mangling. Declare your native function like this:
extern "C" __declspec(dllexport) void foo(HWND wnd)
You can use the dumpbin.exe utility to see DLL exports as well.