MT4 global variables: my new best friend | Forex Factory

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MT4 global variables: my new best friend

  • #1
  • First Post: Jan 19, 2009 4:17am Jan 19, 2009 4:17am
Because my EA runs on a dedicated server 24/7, I have a fear of the server restarting, and all the variables being reset.

I used to store all variables in text files, and reload them when init() was called. Just to primer this, the MT4 shortcut is in my Startup folder, and it will reload right where it left off after the reboot. Can you imagine all your trade management variables being deleted duirng the reboot???

The new approach is to use only global variables in my code. GVs will stay in MTs memory for 4 weeks after they are set, even after reboots and restarts...

So now my init() check to see if each global variable is set, and if not it sends me an email alerting me.

Some uses for them include:
ticket numbers
invisible stops and tps
balance information

Hope this helps somebody.
  • #2
  • Jan 19, 2009 11:13am Jan 19, 2009 11:13am
yes, and it is a good way how to comunicate between mutliple EAs running on same MT4..
  • #3
  • Jan 19, 2009 12:33pm Jan 19, 2009 12:33pm
Can you post some code of how you actually check & set these variables?
  • #4
  • Jan 19, 2009 3:44pm Jan 19, 2009 3:44pm
I am on my mac right now so I can't check but look up MetaEditor help on global variables.
  • #5
  • Jan 19, 2009 8:53pm Jan 19, 2009 8:53pm
I think anyone serious about EA trading is crazy not to use global variables (or at least text files.)

They are powerful.
  • #6
  • Jan 19, 2009 10:35pm Jan 19, 2009 10:35pm
Sorry to keep raving about GVs, but let me explain why I am so excited about them.

In my external variables (which I manipulate through the input GUI on the chart) I have a true/false switch. When I set it to true, I then change other external variables on the menu.

My code see the switch is true, and it updates the GVs. This is wicked cool! I don't have to worry about the values going away, and I can manipulate the EA externally without interfering with the settings (like you would if you restarted the EA)

I actually have several switches that let me change different components of my code. For example, I have a switch for modifying my account information. I have several switches for modifying different strategies.


These are very useful for when there are several trades in play, and you don't want to interfere with the logic controlling them, but maybe some other aspect of the EA.
  • #7
  • Jan 20, 2009 12:48am Jan 20, 2009 12:48am
Here is a sample code.

PHP Code
//+------------------------------------------------------------------+
//| Global Variables test
//+------------------------------------------------------------------+

/*

MetaEditor's explanation

datetime GlobalVariableSet( string name, double value) 
Sets a new value of the global variable. If it does not exist, the system creates a new gloabl variable.
If the function succeeds, the returned value will be the last access time. Otherwise, the returned value will be 0.
To get the detailed error information, one has to call the GetLastError() function. 

Parameters:
name   -   Global variable name. 
value   -   The new numeric value. 
 
Sample:
  //---- try to set new value
  if(GlobalVariableSet("BarsTotal",Bars)==0)
    return(false);
  //---- continue processing

*/

double GV;

//+------------------------------------------------------------------+
//| init
//+------------------------------------------------------------------+
int init()
{
   // Get Global Variable
   GV = GlobalVariableGet("GlobalV");
   if(GV < 1) Print("Can not Get a Global Variable !");
   else Print("Successfully Got a Global Variable !");

   return(0);
}

//+------------------------------------------------------------------+
//| start
//+------------------------------------------------------------------+
int start()
{
   // Set Global Variable
   datetime Set_GV = GlobalVariableSet("GlobalV",TimeCurrent());
   if( Set_GV < 1 ) Print("Can not Set a Global Variable !");

   // last reboot time
   string last_reboot_time = "last_reboot_time = " + TimeToStr(GV, TIME_DATE | TIME_MINUTES);

   // current time
   double Get_GV = GlobalVariableGet("GlobalV");
   string CurrentTime = "GlobalV = " + DoubleToStr(Get_GV,0)+" ("+TimeToStr(Get_GV, TIME_DATE | TIME_MINUTES)+")";
   
   // show comment
   string ln = "n"; < --- note : change "n" to "backslash n"
   Comment(
            last_reboot_time + ln +
            CurrentTime
           );
   
   return(0);
}
  • #8
  • Jan 20, 2009 4:53pm Jan 20, 2009 4:53pm
Yeah, I knew GBs a long long time ago.
They are helpful and much more easier to use than saving data into a notepad using file operations.
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  • #9
  • Jan 20, 2009 7:57pm Jan 20, 2009 7:57pm
I also love Global Variable use in EA's. It's one of the best ways to keep any information you don't want lost.

Glad you found them tdion!
  • #10
  • Jan 20, 2009 9:59pm Jan 20, 2009 9:59pm
I'm just getting used to a happy and chipper Tdion...

But yes, GVs are extremely useful too. I use them in some "collaborative" EA's that consolidate a few methods into one.
  • #11
  • Nov 7, 2010 11:56pm Nov 7, 2010 11:56pm
It made me think that GV can cause conflicts between EAs. Am I correct?
  • #12
  • Nov 9, 2010 12:07pm Nov 9, 2010 12:07pm
only problem with Global Variable is that you only can change with editing the mq4 file

Quoting luiboy
It made me think that GV can cause conflicts between EAs. Am I correct?
I don't know a i did not read though the GV yet. however, as conflicts between EAs that would be need to clear different name for the GV for each EA

anyway why not just save each setting as different ea instant?
  • #13
  • Nov 9, 2010 1:38pm Nov 9, 2010 1:38pm
Quoting mtuppers
different name for the GV for each EA
Yes. this is how it is done. There are many posibilities, for example:

Inserted Code
[color=#7f0055][b]string[/b][/color] [color=#000000]getFullName[/color][color=#000000]([/color][b][color=#7f0055]string[/color][/b] name[color=#000000]){[/color]
   [color=#7f0055][b]return[/b][/color][color=#000000]([/color][color=#000000]WindowExpertName[/color][color=#000000]() +[/color] [color=#000000]Symbol[/color][color=#000000]() +[/color] [color=#000000]Period[/color][color=#000000]() +[/color] name[color=#000000]);[/color]
[color=#000000]}[/color]

[color=#7f0055][b]void[/b][/color] [color=#000000]setVariable[/color][color=#000000]([/color][color=#7f0055][b]string[/b][/color] name[color=#000000],[/color] [color=#7f0055][b]double[/b][/color] value[color=#000000]){[/color]
   [color=#000000]GlobalVariableSet[/color][color=#000000]([/color][color=#000000]getFullName[/color][color=#000000]([/color]name[color=#000000]),[/color] value[color=#000000]);[/color]
[color=#000000]}[/color]

[color=#7f0055][b]double[/b][/color] [color=#000000]getVariable[/color][color=#000000]([/color][color=#7f0055][b]string[/b][/color] name[color=#000000]){[/color]
   [color=#7f0055][b]return[/b][/color][color=#000000]([/color][color=#000000]GlobalVariableGet[/color][color=#000000]([/color][color=#000000]getFullName[/color][color=#000000]([/color]name[color=#000000]));[/color]
[color=#000000]}[/color]
and then use it only through these wrapper functions which will transparently generate unique names.
  • #14
  • Nov 16, 2010 10:59pm Nov 16, 2010 10:59pm
There is a lot more that can be done within MTs native code. Here is a sample of some drag and drop, interprogram communications, and trading right off the charts. You are not restricted to viewing the data that the chart window indicates, I mean the top of the chart window may say EURUSD,M15 but it may contain USDJPY,1H data. Why for? what if your looking for a trade and are analyzing different pairs within your portfolio of tradables, would it not be nice to have them all rotate automaticly within the same window in front of you instead of flipping through each chart window one by one yourself? you can have more then one chart of price data in one window meaning more then one pair, and or time scale. You are not restricted to the time scales that MT has avaible.

the screenshots show some of the capabilities
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  • #15
  • Nov 17, 2010 12:12am Nov 17, 2010 12:12am
Quoting CockeyedCowboy
the screenshots show some of the capabilities
You forgot to attach the source code that produced the examples.
  • #16
  • Nov 18, 2010 2:19am Nov 18, 2010 2:19am
Oh yes, now that I'm back entrenched in my trading life again, MT4 code and I are new buddies. Can't stress how useful the GV is in keeping system stability a priority.
  • #17
  • Nov 19, 2010 12:52am Nov 19, 2010 12:52am
// 4 ######################################################################################################

// prevent typing "GlobalVariableGet" throughout code

double gvg(string Variable_Name)

{ //1

return(GlobalVariableGet(Variable_Name));

} //1

// 5 ######################################################################################################

// prevent typing "GlobalVariableSet" throughout code

bool gvs(string Variable_Name, double Value)

{ //1

return (GlobalVariableSet(Variable_Name, Value));

} //1
  • #18
  • Nov 19, 2010 6:11am Nov 19, 2010 6:11am
Quoting tdion
// 4 ######################################################################################################

// prevent typing "GlobalVariableGet" throughout code
prepend the name in your gvg() function with

WindowExpertName()+Symbol()+Period()

and you will have them always nicely (and automatically) separated for each EA on every chart and timeframe with even less typing.

See my other example above. You basically repeated my example but you left out the neat part where the magic happens that *really* saves a lot of typing and coding.
  • #19
  • Nov 20, 2010 2:22pm Nov 20, 2010 2:22pm
would it not be better
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  • #20
  • Nov 20, 2010 2:47pm Nov 20, 2010 2:47pm
Quoting CockeyedCowboy
would it not be better
For magic numbers I use a hash over name+symbol+timeframe, this is more robust and needs no persistence layer. For global variable names a string will work, no need to convert this to a number (but of course one could use the (auto-generated) magic-number for this too if it already exists).
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