Sharing variables between instances and / or sessions

[Mac]

Hi MQLers,

please advise: within my EA I am using a variable which gets continuously updated based on how the market unfolds for that specific symbol. Given that of course I am going to have my EA run in multiple windows on multiple symbols, a question of concurrency arises. To use a live and typical example: in an ideal world variable XY gets updated within the EURUSD window and the USDJPY window is able to query this new value right afterwards. Where / how should such a variable be declared?

And - what are my options if I wanted that variable to keep its value in between sessions (e.g. during recompile or restart of the terminal)?

Thanks in advance,

Mac

[ydrol]

Hi see

https://docs.mql4.com/globals/GlobalVariableSet

[ydrol]

// You may want to prefix all global variable names with the EA name and testing mode....
// Also for testing you want code to delete all of the test ones ... whose name starts with globalId("")

string globalId(string id)
{
    string m = WindowExpertName()+"/"+IsTesting()+"/"+id+"/";
    return (m);
}

datetime globalSet(string n,double d)
{
    string id = globalId(n);
    datetime ret = GlobalVariableSet(id,d);
    return(ret);
}

double globalGet(string n)
{
    string id = globalId(n);
    double d = GlobalVariableGet(id);
    return (d);
}

[Mac]

Thanks ydrol, this is perfect. I had no idea there are special helpers for this purpose. One last issue remains - how to share a value accross sessions (if I do not want to persist to a file, that is) ...

[ydrol]

They last for 28 days https://docs.mql4.com/globals if unaccessed. That might be enough...