CODEWITHSUNDEEP
c#dlldllimportmql5
Thembekile Mkhombo
Thembekile Mkhombo

Reputation: 87

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.

Upvotes: 1

Views: 943

Answers (1)

Thembekile Mkhombo
Thembekile Mkhombo

Reputation: 87

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);
}

Upvotes: 2

Related Questions