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Create DLL , simplest form example

7 July 2023, 14:57

Lorentzos Roussos

400

Hi!

First things first you need visual studio for this .

Install it , start it up.

Select the programming language
Select the operating system
Select Library
Select Dynamic Link library , it will appear

Click Next

give it a name

Click Create

wait for the slow pc to create the project

This is the first thing you may see , the explorer could be on the right in your setup .

It opens up with the dllMain.cpp in view :

Now , correct me if you are more experienced but ,whatever .cpp file (because we chose c++) you create inside the project could be accessible

in the DLL .

For this one let's pack everything in one file since we s*ck at programming . 😊

So let's create a new cpp file called "mySimpleDLL.cpp" , you can name it whatever you want don't worry.

In the solutions explorerTab right click on the name of the project
Go to menu item "add"
Go to menu item "New item"
From the popup select "C++ file" , if you cant see it click "detailed view" bottom left
Name your file
Hit "add"

Add the following on top of your new cpp file :

Name it name + _EXPORTS
Name it name +_API

Is that important (the naming convention) ? I don't know , someone more experienced can explain.

here is the code form :

#pragma once

#include "pch.h" // use stdafx.h in Visual Studio 2017 and earlier
#include <utility>
#include <limits.h>

#ifdef MYSIMPLEDLL_EXPORTS
#define MYSIMPLEDLL_API __declspec(dllexport)
#else
#define MYSIMPLEDLL_API __declspec(dllimport)
#endif

Excellent , now let's expose a function !

extern "C"
name of api as defined
return type
name of function
function parameters

in code , simple a+b in the return :

extern "C" MYSIMPLEDLL_API int hard_math(int a, int b) {
        return(a+b);
}

Awesome , but does it work ?

On the compile tab on the header :

Click on "Debug" (if it says release skip this step)
Select "Release"

wait for your fast pc to prepare

next to it

select x86 if the DLL is for MT4
select x64 if the DLL is for MT5

click "Build" on the menu on top
click "Build Solution"

If it compiles succesfully you will see this in the console

Cool now , let's find the file (the dll)

under solution explorer right click the name of the project
select "open folder in file explorer"

the file explorer will send you to a folder looking like this :

Go one level up , you need to be in the folder marked with the pink marker

Navigate in the "Release" folder
Your dll file is there for x86 (32bit)

Copy it and move it to your expert advisor folder to test it .

For the first test create a folder in experts called mySimpleDLL and place the mySimpleDLL.dll dll in that folder .

create a test1.mq4 file in the editor , it should look like this

In the test1.mq4 we add this to the header to import the function from the dll :

#import "mySimpleDLL.dll" 
int hard_math(int a,int b);
#import

let's see if it does not work.

this is the source code :

#property version   "1.00"
#property strict
#import "mySimpleDLL.dll" 
int hard_math(int a,int b);
#import
int OnInit()
  {
  int result=hard_math(3,5);
  Print("DLL says "+IntegerToString(result));
  return(INIT_SUCCEEDED);
  }

void OnDeinit(const int reason)
  {
  }

void OnTick()
  {
  }