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Questions regarding global variables (and some other stuff)

  • #1
  • First Post: Sep 12, 2018 2:38pm Sep 12, 2018 2:38pm
So I'm working on setting up multiple EA's on MT4. I would like to have globals make changes to multiple EA's at once. For example, If I wanted to pause trading, I could change a pause = n to pause = y, would that actually make changes on all of the EA's at once? Additionally, is it possible for an EA to change a global variable? For example, a variable that would be a total number of all trades open on all charts. So I have 5 trades open, the global variable would actually reflect 5, and if another one is opened it would reflect 6. Is that possible? I know these are somewhat noobie questions, but I'm still in the structure phase of putting this together and want to make sure it is something that can be done before I waste a bunch of time on it.
  • #2
  • Sep 12, 2018 3:35pm Sep 12, 2018 3:35pm
Quoting Naosblue
So I'm working on setting up multiple EA's on MT4. I would like to have globals make changes to multiple EA's at once. For example, If I wanted to pause trading, I could change a pause = n to pause = y, would that actually make changes on all of the EA's at once? Additionally, is it possible for an EA to change a global variable? For example, a variable that would be a total number of all trades open on all charts. So I have 5 trades open, the global variable would actually reflect 5, and if another one is opened it would reflect 6. Is that possible?...
yes
  • #3
  • Sep 12, 2018 3:49pm Sep 12, 2018 3:49pm
Quoting Naosblue
So I'm working on setting up multiple EA's on MT4. I would like to have globals make changes to multiple EA's at once. For example, If I wanted to pause trading, I could change a pause = n to pause = y, would that actually make changes on all of the EA's at once? Additionally, is it possible for an EA to change a global variable? For example, a variable that would be a total number of all trades open on all charts. So I have 5 trades open, the global variable would actually reflect 5, and if another one is opened it would reflect 6. Is that possible?...
second yes.

you can do from any expert advisor any change what is possible with global variables. and you can read this variables in any expert advisor /indicator...
  • #4
  • Sep 12, 2018 5:12pm Sep 12, 2018 5:12pm
Quoting sakisf
yes
Quoting dukas_trader
second yes.


Excellent, thank you very much for your time. That should cut down on extra steps on every single EA.
  • #5
  • Sep 12, 2018 10:23pm Sep 12, 2018 10:23pm
I wouldn't use the terminal-global-variables because I've seen a lot of bug complaints with them on the mql5 forums. Also, they can only store values of type double. If you want to communicate between EAs (same terminal) the best way is via custom chart events. e.g. EA can send a message to other charts and any EA running on that chart can pick up the message from the OnChartEvent event handler. Another way to implement is by using a CSV file in shared read/write. Then there's the OOP options which are super easy... but more advanced than simple low level api functions.
  • #6
  • Edited 11:41pm Sep 12, 2018 10:54pm | Edited 11:41pm
Quoting Naosblue
So I'm working on setting up multiple EA's on MT4. I would like to have globals make changes to multiple EA's at once. For example, If I wanted to pause trading, I could change a pause = n to pause = y, would that actually make changes on all of the EA's at once? Additionally, is it possible for an EA to change a global variable? For example, a variable that would be a total number of all trades open on all charts. So I have 5 trades open, the global variable would actually reflect 5, and if another one is opened it would reflect 6. Is that possible?...
A global can be used to set multiple experts.Is the faster way to do it.You can "encode" whatever information you want to transmit into a double.
for ex.
global=1 ---> buy signal
global=2 ---> sell signal
global=3 ---> close all trades
etc..
Your imagination is the only limit on how a double can be used to transmit information.Use multiple globals to divide the info your experts need to intercommunicate.
Think at the binary system used by computers.Any info can be encoded and transmitted using only 0 and 1.

Setting the global variable.
Inserted Code
   string globalName="GLOBAL";
   double globalValue=1;
   GlobalVariableSet(globalName,globalValue);
Getting the global,testing the value and setting the new value
Inserted Code
 if(GlobalVariableGet(globalName)==1)
  {
    //do stuff here and set the new global value
    GlobalVariableSet(globalName,2);
  };
A simple solution is way better and faster than a complicated one.
It's show time
  • #7
  • Sep 13, 2018 6:57am Sep 13, 2018 6:57am
Quoting Nicholishen
I wouldn't use the terminal-global-variables because I've seen a lot of bug complaints with them on the mql5 forums. Also, they can only store values of type double. If you want to communicate between EAs (same terminal) the best way is via custom chart events. e.g. EA can send a message to other charts and any EA running on that chart can pick up the message from the OnChartEvent event handler. Another way to implement is by using a CSV file in shared read/write. Then there's the OOP options which are super easy... but more advanced than simple...
many programm wrong or to complicated,

global variables are very easy to use and very secure if you programm any error handling possiblity inside, what you have to do always in 1-2 levels in any way. its much faster then csv, and for controlling many experts inside one expert or other structures its a very good solution, you can also use it for simple check if the magicnumber is already used,... control one sound event expert one time, so no sounds are killed by any other expert sound same time........endless possibilities....
  • #8
  • Edited 7:38am Sep 13, 2018 7:23am | Edited 7:38am
This is what I do to share the GV between indis/eas:

Inserted Code
(Globals)
enum calcmodus {
    mod1 = 0, // HL
    mod2 = 1 // OC
};
extern calcmodus calcmode = 0; // Calculation mode HL/OC
extern int pr = 6; //Smoothing period
 
(Init)
if (GlobalVariableCheck("calcmode" + _Symbol) == false) GlobalVariableSet("calcmode" + _Symbol, calcmode); // set initial
if (calcmode != GlobalVariableGet("calcmode" + _Symbol)) GlobalVariableSet("calcmode" + _Symbol, calcmode); // if applied differently on new indi or ea (to change the others too)
if (GlobalVariableCheck("smoothper" + _Symbol) == false) GlobalVariableSet("smoothper" + _Symbol, pr);
if (pr != GlobalVariableGet("smoothper" + _Symbol)) GlobalVariableSet("smoothper" + _Symbol, pr);
GlobalVariablesFlush();
 
(OnCalculate)
if (calcmode != (calcmodus)GlobalVariableGet("calcmode" + _Symbol) || pr != (int)GlobalVariableGet("smoothper" + _Symbol)) {
 calcmode = (calcmodus)GlobalVariableGet("calcmode" + _Symbol);
 pr = (int)GlobalVariableGet("smoothper" + _Symbol);
} // to detect changes and apply them

That's how I use it (in binary mode like boolean or with integers to avoid issues that Nicolishen describes). Then on 2nd-3rd indi/ea, you repeat the same code. When you add a new indi/ea, you make sure it starts at desired mode and when you change one then the others change too.

Add these both on a chart and change the calculation mode or smoothing period or both on one of the two to see how they operate, then go change the other or put it back to default. You can also change the value for both of them through tools > global variables (F3).
Attached File(s)
File Type: ex4 WaveletTrans.ex4   43 KB | 585 downloads
File Type: ex4 WaveletTransAdd.ex4   48 KB | 583 downloads
  • #9
  • Sep 13, 2018 7:46am Sep 13, 2018 7:46am
Thank you all for all your information, folks. I'm still a novice programmer and trader, and started taking existing EA's and picking them apart to figure how they work. There's not exactly a ton of EA's that I have run across that utilize them in the first place, so it is uncharted water for me.
  • #10
  • Sep 13, 2018 9:27am Sep 13, 2018 9:27am
Quoting sakisf
This is what I do to share the GV between indis/eas: (Globals) enum calcmodus { mod1 = 0, // HL mod2 = 1 // OC }; extern calcmodus calcmode = 0; // Calculation mode HL/OC extern int pr = 6; //Smoothing period (Init) if (GlobalVariableCheck("calcmode" + _Symbol) == false) GlobalVariableSet("calcmode" + _Symbol, calcmode); // set initial if (calcmode != GlobalVariableGet("calcmode" + _Symbol)) GlobalVariableSet("calcmode" + _Symbol, calcmode); // if applied differently on new indi or ea (to change the others too) if (GlobalVariableCheck("smoothper"...
Any solution for how to share information across mult-terminals, multi-accounts, multi-strategies... other that writing into a CSV file or some DLL (which I dont have the skill to develop in)?

Also / is there a limitation on the number of global variables or how frequently can I update them. I don't think there is physical disk I/O involved with every update. It's definitely faster than writing to a custom csv.
Staying in my lane...
  • #11
  • Sep 13, 2018 10:24am Sep 13, 2018 10:24am
Quoting VEEFX
{quote} Any solution for how to share information across mult-terminals, multi-accounts, multi-strategies... other that writing into a CSV file or some DLL (which I dont have the skill to develop in)? Also / is there a limitation on the number of global variables or how frequently can I update them. I don't think there is physical disk I/O involved with every update. It's definitely faster than writing to a custom csv.
Any solution for how to share information across mult-terminals

--> use pipes.

multi-accounts

--> use program from broker or best own api

multi-strategies
--> extrem easy and many possibilities, global variable is one of them

most easy and best is own api of course

is there a limitation on the number of global variables or how frequently can I update them

--> you have enough for this to use, and its updated like any other variable just in time when programm line is running.
its simple basic way of programming, when you use many ways of trading, controling, sound, managing,..... by using global variables.
maybe not most nice way against own api and own frontend, but extrem easy.
for glibal variables read all rules in manuel, like when it will be deleted when not used for longer time.... and so on. but all this are extrem easy parts that any error checking system can handle in a second. and a error checking system is what is first anyone should have programmed for any case what can happen in trading, connection problem, hardeware problem, broker problem, program problem.......... and then to use this in any program.
  • #12
  • Last Post: Sep 13, 2018 11:50am Sep 13, 2018 11:50am
Quoting VEEFX
{quote} Any solution for how to share information across mult-terminals, multi-accounts, multi-strategies... other that writing into a CSV file or some DLL (which I dont have the skill to develop in)? Also / is there a limitation on the number of global variables or how frequently can I update them. I don't think there is physical disk I/O involved with every update. It's definitely faster than writing to a custom csv.
The speed/disk IO would be approximately the same, depending on how often you change a GV (or flush them) or have it write the settings to csv. If you want to save other data (rates etc) probably you shouldn't use GVs. I haven't found any information on GV limit, don't think there's one. I am using more than a hundred atm.

Regarding network sharing, what dukas_trader said above should be sufficient (pipes / python backbone). I am using a hard linked file (gvariables.dat) which is shared through syncthing to my other pc but data is not sensitive nor time-critical, only settings so such simple sharing is sufficient.
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