Integrate DLL and MT4/5 VS2010 example

Aim

We would like to create a Win32 DLL by Visual Studio 2010. A script running on MT4 will then use that DLL as an example.

Learning Source

VS 2010 example

Steps

• Create Win32 DLL project

• In stdafx.h, add

#define _DLLAPI extern "C" __declspec(dllexport)

• In MQL5DLLSamples.cpp

// MQL5DLLSamples.cpp : Defines the exported functions for the DLL application.
//

#include "stdafx.h"


//+------------------------------------------------------------------+
//| Passing and receving of simple variables                         |
//+------------------------------------------------------------------+
_DLLAPI int __stdcall fnCalculateSpeed(int &res1,double &res2)
  {
   int    res_int=0;
   double res_double=0.0;
   int    start=GetTickCount();
//--- simple math calculations
   for(int i=0;i<=10000000;i++)
     {
      res_int+=i*i;
      res_int++;
      res_double+=(double)i*(double)i;
      res_double++;
     }
//--- set calculation results
   res1=res_int;
   res2=res_double;
//--- return calculation time
   return(GetTickCount()-start);
  }
//+------------------------------------------------------------------+
//| Filling the array with values                                    |
//+------------------------------------------------------------------+
_DLLAPI void __stdcall fnFillArray(int *arr,const int arr_size)
  {
//--- check input variables
   if(arr==NULL || arr_size<1) return;
//--- fill array with values
   for(int i=0;i<arr_size;i++) arr[i]=i;
  }
//+------------------------------------------------------------------+
//| The substring replacement of the text string                     |
//| the string is passed as direct reference to the string content   |
//+------------------------------------------------------------------+
_DLLAPI void fnReplaceString(wchar_t *text,wchar_t *from,wchar_t *to)
  {
   wchar_t *cp;
//--- parameters checking
   if(text==NULL || from==NULL || to==NULL) return;
   if(wcslen(from)!=wcslen(to))             return;
//--- search for substring
   if((cp=wcsstr(text,from))==NULL)         return;
//--- replace it 
   memcpy(cp,to,wcslen(to)*sizeof(wchar_t));
  }
//+------------------------------------------------------------------+
//| Call for the crush                                               |
//+------------------------------------------------------------------+
_DLLAPI void __stdcall fnCrashTest(int *arr)
  {
//--- wait for receipt of a zero reference to call the exception
   *arr=0;
  }
//+------------------------------------------------------------------+

• Build the dll file and put that into MQL4/Libraries in the MT4 folder
• Prepare the mql4 script in MQL4/Scripts, DLLTest.mq4

//+------------------------------------------------------------------+
//|                                                      DLLTest.mq4 |
//|                        Copyright 2020, MetaQuotes Software Corp. |
//|                                             https://www.mql5.com |
//+------------------------------------------------------------------+
#property copyright "Copyright 2020, MetaQuotes Software Corp."
#property link      "https://www.mql5.com"
#property version   "1.00"
#property strict
//---
#import "MQL5DLLSamples.dll"
int  fnCalculateSpeed(int &res1,double &res2);
void fnFillArray(int &arr[],int arr_size);
void fnReplaceString(string text,string from,string to);
void fnCrashTest(int arr);
#import
//+------------------------------------------------------------------+
//| Script program start function                                    |
//+------------------------------------------------------------------+
void OnStart()
  {
//---
   //--- calling the function for calculations
   int    speed=0;
   int    res_int=0;
   double res_double=0.0;

   speed=fnCalculateSpeed(res_int,res_double);
   Print("Time ",speed," msec, int: ",res_int," double: ",res_double);
//--- call for the array filling
   int    arr[];
   string result="Array: "; 
   ArrayResize(arr,10);
   
   fnFillArray(arr,ArraySize(arr));
   for(int i=0;i<ArraySize(arr);i++) result=result+IntegerToString(arr[i])+" ";
   Print(result);
//--- modifying the string
   string text="A quick brown fox jumps over the lazy dog"; 
   
   fnReplaceString(text,"fox","cat");
   Print("Replace: ",text);
//--- and finally call a crash
//--- (the execution environment will catch the exception and prevent the client terminal crush)
   fnCrashTest(NULL);
   Print("You won't see this text!");
//---
  }
//+------------------------------------------------------------------+

• Build that script and test on MT4
• DONE