How to write/read variables to/from a file? | Forex Factory

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How to write/read variables to/from a file?

  • #1
  • First Post: Nov 5, 2013 2:58pm Nov 5, 2013 2:58pm
Hello,

I've searched here and in mql4.com but do not understand how works the file operations in practice.

3 variables from an EA should be written into a file (.txt) and another EA should can read that values to get them as variables.


Does anyone have a simple code example for these two thinks?


Thank you!
  • #2
  • Nov 5, 2013 3:17pm Nov 5, 2013 3:17pm
Quoting Cash4Life
Hello, I've searched here and in mql4.com but do not understand how works the file operations in practice. 3 variables from an EA should be written into a file (.txt) and another EA should can read that values to get them as variables. Does anyone have a simple code example for these two thinks? Thank you!
Hi My Friend,

if both EA's run at same MT4 Instance then you can learn about Global Variables Set and Get.. so no need to write any file

Best regards.
  • #3
  • Nov 5, 2013 4:31pm Nov 5, 2013 4:31pm
Quoting Cash4Life
..
Kidas is right. If you want to send data between EAs in 1 terminal GlobalVariables are much better. If you want to send data between 2 terminals NamesPipes are the best way to go. But here is an example anyways.

Inserted Code
fileName = Symbol()+Period()+".csv";

 // updated file once per bar
   if(lastupdate != Time[0]) 
   {
      fileHandle = FileOpen(fileName,FILE_CSV|FILE_READ | FILE_WRITE);
   
      FileSeek(fileHandle, 0, SEEK_END); // Write at the end of the file.
      string data = up[0]+"," + fractals+","+zigzag+","+count+","+Time[1];
      FileWrite(fileHandle,data);
      FileClose(fileHandle);
      
      lastupdate = Time[0];
   }
  • #4
  • Nov 5, 2013 4:48pm Nov 5, 2013 4:48pm
Thank you. Yes I want send data between 2 terminals on 2 different computers therefore I try the file operations with .txt
I do not understand how the code looks to write or read the variables...
  • #5
  • Nov 5, 2013 4:51pm Nov 5, 2013 4:51pm
Quoting Cash4Life
Thank you. Yes I want send data between 2 terminals on 2 different computers therefore I try the file operations with .txt I do not understand how the code looks to write or read the variables...
How will you get the .txt file from one PC to the other ? WinAPI ?
20 pips a day isn't too much to ask . . .
  • #6
  • Nov 5, 2013 4:53pm Nov 5, 2013 4:53pm
Quoting RaptorUK
{quote} How will you get the .txt file from one PC to the other ? WinAPI ?

If he doesn't want to do it in real time he can just copy and paste them . Or else he should take a look at a database.
  • #7
  • Nov 5, 2013 4:55pm Nov 5, 2013 4:55pm
I can distribute the file to several computers over NAS
  • #8
  • Nov 5, 2013 5:11pm Nov 5, 2013 5:11pm
Quoting Cash4Life
I can distribute the file to several computers over NAS
It is not as easy as you think it will be. FileRead and Write just access files in the own mt4 installation sub folders. Writing a file to a NAS isn't a trivial task. Either use a DLL or do some research on symlinks.


Edit: http://www.sevenforums.com/tutorials...s-windows.html
  • #9
  • Nov 5, 2013 5:25pm Nov 5, 2013 5:25pm
I have a tool to sync the File that already run, is not the problem. But the Problems are the thinks in #Post1... ??
  • #10
  • Nov 5, 2013 5:36pm Nov 5, 2013 5:36pm
Quoting Cash4Life
I have a tool to sync the File that already run, is not the problem. But the Problems are the thinks in #Post1... ??
Well I have already given you an example on how to write to a file.
This covers pretty much everything you need.
http://book.mql4.com/functions/files

http://docs.mql4.com/files/FileReadNumber & http://docs.mql4.com/files/FileReadString

There is absolutely no magic involved. Why not create a sample ea to explore those operations? It's takes like a maximum of 10 lines of code.
  • #11
  • Nov 5, 2013 5:48pm Nov 5, 2013 5:48pm
Thank you ok I will try it again
  • #12
  • Nov 6, 2013 3:10am Nov 6, 2013 3:10am
Quoting Cash4Life
I have a tool to sync the File that already run, is not the problem. But the Problems are the thinks in #Post1... ??
How does it determine if the file is open and being written to ?
20 pips a day isn't too much to ask . . .
  • #13
  • Nov 6, 2013 5:54am Nov 6, 2013 5:54am
Quoting RaptorUK
{quote} How does it determine if the file is open and being written to ?
If you use the approach with mklink will mt4 be able to handle 1 r ead & write and 1 read only access simultaneously?

I am writing to a csv file with a mt4 ea and got a read only connection open with Java at the same time without any problems, but have you experience what happens if you use 2 EAs for that?
  • #14
  • Nov 6, 2013 6:15am Nov 6, 2013 6:15am
Quoting Kilian19
{quote} If you use the approach with mklink will mt4 be able to handle 1 r ead & write and 1 read only access simultaneously? I am writing to a csv file with a mt4 ea and got a read only connection open with Java at the same time without any problems, but have you experience what happens if you use 2 EAs for that?
I don't have specific experience with MT4 and EAs trying to access the same file but I have experience with Windows apps trying to access the same file and I know it can be problematical if not handled with care, for example, the app reading should not try to do so until the writing app has finished, it sounds trivial but isn't. Even opening the file with exclusive access didn't solve all the problems on it's own . . . perhaps things are better these days, it was a few years ago when I was involved with this.
20 pips a day isn't too much to ask . . .
  • #15
  • Nov 6, 2013 6:21am Nov 6, 2013 6:21am
Quoting RaptorUK
...
hmm I don't think that mt4 does a good job at it. If I remember correctly

Opening file with mql4 and than start reading it simultaneously with Java works fine.
Opening the reading connection first with Java and trying to open the file with mql4 gives you an error.

Anyways lets agree that files are not the optimal way to transfer data.
  • #16
  • Nov 6, 2013 6:26am Nov 6, 2013 6:26am
Quoting RaptorUK
{quote} How does it determine if the file is open and being written to ?
The tool simple copy the file on a NAS in intervall (every second...). Another tool on the other computer read in intervall from the NAS. Problems with concurrent access does not exist because the NAS regulates this.


With the example i get it, the file is created and the values come in. But the values ​​are always added on a new line. Gradually the file is getting bigger and bigger. I just need the current values. It would be possible to overwrite the values ​​so there is always only one actual line?

Inserted Code
fileName = Symbol()+Period()+".csv";


     fileHandle = FileOpen(fileName,FILE_CSV|FILE_READ | FILE_WRITE);
  
     FileSeek(fileHandle, 0, SEEK_END); // Write at the end of the file.
     string data = 123+","+456+","+789+","+777+","+Ask;
     FileWrite(fileHandle,data);
     FileClose(fileHandle);
  • #17
  • Nov 6, 2013 6:34am Nov 6, 2013 6:34am
All right! SEEK_SET is the solution
Thank you
  • #18
  • Last Post: Nov 6, 2013 9:20am Nov 6, 2013 9:20am
For such a purpose one uses:

mailslots: http://msdn.microsoft.com/en-us/libr...(v=vs.85).aspx

or,

named pipes: http://msdn.microsoft.com/en-us/library/aa365590.aspx
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