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Creating Metatrader DLLs with Lazarus / Free Pascal

  • #101
  • Apr 29, 2017 3:09pm Apr 29, 2017 3:09pm
Quoting 7bit
A better example of the moving average indicator or of an indicator of such a type in general has been requested in this thread and here it is. Attached are the Lazarus Project and the mql4 source and additionally I post the source code here in the text area so you can have a quick look at it without downloading and unzipping. The comments in the code describe what is going on in great detail, so I don't need to write anything more and simply post the code, the code will explain itself. Here it is: mql4 code of the indicator /** * This serves as...

Could you please provide the content of the dll as file and additional information to it? It seams very interresting to me.
  • #102
  • Sep 3, 2018 11:29pm Sep 3, 2018 11:29pm
This doesn't work anymore, the dlls and mql code doesn't do anything.
  • #103
  • Dec 7, 2018 2:20am Dec 7, 2018 2:20am
MT4 also developed by its own company does not work why the DLL. Script under DLLSampleTester.mq4
  • #104
  • Mar 12, 2019 2:15pm Mar 12, 2019 2:15pm
Hey, DLL coders!

I've been doing my DLL development in Delphi, which AFAIK is the commercial product that inspired Lazarus. I have Delphi 10 Seattle, though I prefer to work with Delphi 2010, it is significantly faster and easier to work with (as long as you don't need 64-bit executables, which MT4 does not). Don't ya love those "upgrades" that are a big step backwards? My old 1.0 GHz Windows NT box booted in under 4 seconds... (deep sigh)...

Here is some information for planning a MT4 DLL project using Delphi (which should also apply to Lazarus):

  1. Delphi has a good source code debugger, but the sticky problem is that to debug a DLL you need to load the entire Metatrader application as a host for the DLL. Metatrader builds 226 and higher have protection features built in that will detect if it is being run inside a debugger and will refuse to run. So if you want to debug your DLL with the debugger you need to run it on Build 225 or earlier. That brings with it several disadvantages such as

    1. There are no servers that serve live data for these early builds.
    2. The early builds do not support all the MQL language features that later builds support, such as structs, #ifdef, OOP, etc.
    3. There is no MQL source code debugger in Build 225.
    4. The HST file format has changed since Build 225, so getting test data to work with is not as easy as copying some files from a more recent build. I've worked around this by transferring a lightly modified period_converter script from build 225 to a current build and running it there to create an HST file in the older format.


  2. One cool solution for getting around the need to work with Build 225 is to write your Delphi code modularly so it can either be compiled into a DLL or into a statically linked executable. Then create a simple test bench form in Delphi/Pascal to exercise and debug the basic functionality of your code as a statically linked module before compiling it as a DLL.
  3. MQL will not pass scalar data types as VAR parameters, only arrays can be passed. An easy workaround is to declare the scalars as an array of size 1. On the Delphi/Pascal side, it can be declared as a scalar. (I don't know if more recent builds will accept scalar VARs).
  4. MT4 loads a single DLL with a single shared memory space for all instances of an indicator or EA, even if they are on separate charts (their documentation said otherwise but they lied -- it may have been corrected recently). Be sure to code your DLL in anticipation of this, particularly if the DLL has any sort of persistent storage.
  5. MT4 can potentially call an EA's start() function a second time before the first call has returned. Design your function calls to be reentrant.
  6. Remember to use stdcall in the Delphi function header. Metatrader crashing either at the time your DLL runs or at the time you close the MT4 program is a result of omitting this. Note: if you can't even start up MT4 without it crashing immediately, the fix is to navigate to the profiles folder of your MT4, find which profile it is loading and edit the chartNN.CHR manually with a text editor to delete the reference to your faulty indicator/EA.

Metatrader MQL is reasonably good for simple coding, but it just can't compare with an industrial strength compiler. For those of us who don't believe in bringing a knife to a gunfight -- cheers!

Sure I have a trading plan. Buy low. Sell high. What's yours?
  • #105
  • Last Post: Apr 15, 2023 11:48am Apr 15, 2023 11:48am
Hi, sorry for digging up this old thread, but since i cannot start a new one yet, this seemed to be the best fit for my Topic.
I want to run MT4 and at the same time my own java application. I want both to communicate with each other.

My concept to realise this is to call a dll from mql, open my java tool with this dll.
So i am in same memory space and i want to work with stdin and stdout to establish a communication.
But i did not come to this point, yet.

So far i have made some simple java app with only a text to test my setup:

Inserted Code
import javax.swing.*;
public class SystemOutTest {
       public static void main(String[] args) throws InterruptedException {
          JFrame frame = new JFrame("Text Window");
          JLabel label = new JLabel("Hello, World!");
          frame.add(label);
          frame.setSize(200, 100);
          frame.setVisible(true);
          
          Thread.sleep(9000);
       }
    }

I also did the DLL in Pascal / Delphi, to run my .jar File:

Inserted Code
library JarLauncher;
uses
    Windows, ShellAPI;
 
function LaunchJar(const AFileName: string; const AArguments: string): Integer; stdcall;
  var
  JavaPath: string;
begin
  // Locate the Java executable
  JavaPath := 'C:\Program Files (x86)\Java\jre1.8.0_361\bin\java.exe';
 
  Result := ShellExecute(
    0,
    nil,
    'java.exe',
    '-Xmx1024M -Xms1024M -jar testpilot.jar',
    nil,
    SW_SHOW
);
 
end;
 
 
exports
  LaunchJar;
begin
end.


And my MQL, looking like this:

Inserted Code
#import "JarLauncher.dll"
int LaunchJar(string AFileName, string AArguments);
#import
void OnInit()
{
   // string jarFile = "C:\\path\\to\\testpilot.jar";
   string jarFile = "testpilot.jar";
   string arguments = "";
   
   int result = LaunchJar(jarFile, arguments);
   if (result <= 0)
   {
      Print("Failed to launch JAR file!");
   }
   else
   {
      Print(result);
   }
   Sleep(9000);
}



I had my struggle with getting everything to 32Bit, so this is done. Got no Errors whatsoever.
My Output in MT4 is this:
Inserted Code
2023.04.15 20:43:28.558    maybeload [DJI30],H1: 42
2023.04.15 20:43:26.064    Expert maybeload [DJI30],H1: loaded successfully

.jar starts without Problems, shows the Window with text (i know, it doesnot close properly, will fix later!)

BUT, wenn i start my EA, it loads the dll, it seems like the Thread is terminated immediately. Just some blink of an eye console window is popping up.
I figured it has something to do with threadhandling from MQL.
But im open for any leads... wasted some Days without progress now.

Im Open for another concept to get from MT4 to Java, too.
Maybe i would go to StackOverFlow but i found lot of helpful code and ideas here, so i stuck to you

Thanks a lot!
Duke
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