Is it possible to save array info? | Forex Factory

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Is it possible to save array info?

  • #1
  • First Post: Aug 29, 2008 10:16am Aug 29, 2008 10:16am
Hi,


I would like to know if there is any way of storing array data info, that can be accessed in the fututre.
I have an EA that stores values in arrays and I want that those values are always accessible, even when I have to re-initialize metatrader. As I understand, and correct me if I'm wrong, MT4 only stores those values while the program is running and, whenever it shut downs and is run again the process starts all over again.


Thanks in advance for your help,


Joaquim Fonseca
  • #2
  • Aug 29, 2008 9:58pm Aug 29, 2008 9:58pm
Hi,

Check out "Global variables of client terminal" (GV) here:
http://book.mql4.com/variables/globals.

GV's can last up to 4 weeks when not utilized according to the tutorial.

I have not used it on arrays. You may have to save each element of the array individually.

Hope this helps.

Pipmaestro
  • #3
  • Aug 31, 2008 10:18am Aug 31, 2008 10:18am
I imagine you need to save many values since you are using an array to store them.
Regardless I wouldnt advise trying to store anything (long term) in the Global Variables.
You should do what all programs on all platforms do, namely :
Load and save the data to and from a disk file implemented during the Init() and DeInit() procedures of your EA or indicator.
  • #4
  • Sep 1, 2008 12:48pm Sep 1, 2008 12:48pm
Quoting pipmaestro
Hi,

Check out "Global variables of client terminal" (GV) here:
http://book.mql4.com/variables/globals.

GV's can last up to 4 weeks when not utilized according to the tutorial.

I have not used it on arrays. You may have to save each element of the array individually.

Hope this helps.

Pipmaestro

Hi Pipmaestro,

Thanks for this tip, I wasnīt aware that this kind of variables existed, and it will be useful for simpler programs. Unfortunately for this one it's not the ideal solution.

Thanks,

Joaquim Fonseca
  • #5
  • Sep 1, 2008 1:01pm Sep 1, 2008 1:01pm
i do it with text files...

in my init() i open the file and read them back into my array.

cheers

edit) rangebound hit the nail on the head.
  • #6
  • Sep 1, 2008 1:12pm Sep 1, 2008 1:12pm
Quoting rangebound
I imagine you need to save many values since you are using an array to store them.
Yes, you're right.

Regardless I wouldnt advise trying to store anything (long term) in the Global Variables.
You should do what all programs on all platforms do, namely :
Load and save the data to and from a disk file implemented during the Init() and DeInit() procedures of your EA or indicator.
Hi Rangebound,

Thatīs exactely what I want to do, I just don't know how to do it. I would like the EA to save in a file the same it is saved in the array. Can you point me to any tutorial, or can you send me any EA that has this feature, so I can study how it works?

Thanks,

Joaquim Fonseca
  • #7
  • Sep 1, 2008 1:21pm Sep 1, 2008 1:21pm
here's the API for file functions:

http://docs.mql4.com/files
  • #8
  • Sep 1, 2008 2:08pm Sep 1, 2008 2:08pm
I long for the days of better array functions. Some languages have a recursive "serialize" function that takes an array and converts it into a string for output. Sadly... MQL does not have that.

I think the best you're going to get is the FileWriteArray command.

Docs:
http://docs.mql4.com/files/FileWriteArray

I don't know how well it handles multi-dim arrays, but it probably handles single dim arrays pretty well.

There's also a FileReadArray for reading stuff back in.
http://docs.mql4.com/files/FileReadArray

One icky thing is the whole "Before reading, make sure that the array is large enough. Returns the amount of actually read elements." If you're dealing with a dynamically-sized array this could be a real PITA.
  • #9
  • Sep 1, 2008 6:52pm Sep 1, 2008 6:52pm
JFonseca - what arrays are you wanting to save? int/double/string ? How many dimensions? Dynamic or static?

Post the info on the array(s)

EG

int mysubtotals [100];

double mytrades [][5];

string mydynamicheadingsandsubheadings [][]
  • #10
  • Sep 2, 2008 1:18pm Sep 2, 2008 1:18pm
Quoting rangebound
JFonseca - what arrays are you wanting to save? int/double/string ? How many dimensions? Dynamic or static?

Post the info on the array(s)

EG

int mysubtotals [100];

double mytrades [][5];

string mydynamicheadingsandsubheadings [][]

Hi Rangebound,

I have an array with 50 lines and 4 columns of double values, where each line info is deleted if certain conditions are met. This is checked everytime the EA is run, in this case once per hour. I would like the EA to read the existing info from the file to the array, the EA does the necessary check and modifications, and then save it again to the file.

double Moments [50,4];

Thanks for your help,

J Fonseca
  • #11
  • Sep 2, 2008 2:45pm Sep 2, 2008 2:45pm
Example of how to load and save your array data

The first time you run the EA, it will Alert that there was an error loading the data obviously because the data file does not exist.

Subsequent runs will report the "last Open / Close / High"
which are the last recorded values before the EA was removed.


You must Add & Remove the EA in order for the Init / deinit rountines to fire ... you cant just turn the EA on and off using the tool bar button.
Attached File(s)
File Type: mq4 examplesavearray.mq4   3 KB | 402 downloads
  • #12
  • Last Post: Sep 2, 2008 8:07pm Sep 2, 2008 8:07pm
Hi Rangebound,

I could not have asked for an answer any better than the on you gave me. Now I don't have the time to read carefully the EA you attached, but at a first glance, it seems that it was the answer that I needed.

Once more, many thanks,

Joaquim Fonseca
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