how to retain variable if mt4 needs to restart?

[bobo1974]

Hi all,

What are the methods to retain a variable value if mt4 was restarted?

i can only think of either

1. storing the information in the comment of an order

2. save the info in a csv file and read it back later

Thanks 

[Stanislav Korotky]

bobo1974:

What are the methods to retain a variable value if mt4 was restarted?

Use global variables.

[Marco vd Heijden]

Global variables will be lost !

use

FileWrite()

To store your data then use FileRead(datatype) to read the data back into the EA. https://www.mql5.com/en/docs/files

A simple check call for:

ENUM_TERMINAL_INFO_INTEGER

Identifier	Description
TERMINAL_CONNECTED	Connection to a trade server

Can alert you when the connection drops.

*NOTE that comments can change !!, it's not a secure or reliable solution.

[bobo1974]

Marco vd Heijden:

Global variables will be lost !

use

To store your data then use FileRead(datatype) to read the data back into the EA. https://www.mql5.com/en/docs/files

A simple check call for:

ENUM_TERMINAL_INFO_INTEGER

Identifier	Description
TERMINAL_CONNECTED	Connection to a trade server

Can alert you when the connection drops.

*NOTE that comments can change !!, it's not a secure or reliable solution.

hi

 is this function going to write to an external file and read back later? 

[Marco vd Heijden]

bobo1974:

hi

 is this function going to write to an external file and read back later? 

No that will alert you that your terminal has lost it's connection.

Can be used in combination with

Alert() 
PlaySound()
MessageBox()
SendNotification()
SendMail()

And etc.

To store your data use 

FileWrite()

To read it

FileReadArray	Reads arrays of any type except for string from the file of the BIN type
FileReadBool	Reads from the file of the CSV type a string from the current position till a delimiter (or till the end of a text line) and converts the read string to a value of bool type
FileReadDatetime	Reads from the file of the CSV type a string of one of the formats: "YYYY.MM.DD HH:MM:SS", "YYYY.MM.DD" or "HH:MM:SS" - and converts it into a datetime value
FileReadDouble	Reads a double value from the current position of the file pointer
FileReadFloat	Reads a float value from the current position of the file pointer
FileReadInteger	Reads int, short or char value from the current position of the file pointer
FileReadLong	Reads a long type value from the current position of the file pointer
FileReadNumber	Reads from the file of the CSV type a string from the current position till a delimiter (or til the end of a text line) and converts the read string into double value
FileReadString	Reads a string from the current position of a file pointer from a file
FileReadStruct	Reads the contents from a binary file  into a structure passed as a parameter, from the current position of the file pointer

As per: https://www.mql5.com/en/docs/files

You have several options.

* Build an EA that simply scans all orders upon initialization, and handles it from there.

That will work anytime and with all positions, but you can not recover exact information about specific symbols, it means all orders will be handled to a set of pre defined values.

Unless you specify the settings, for each symbol, and load them upon detection.

* Store the current position data into a file then read that data back into the EA in case of a failure.

This requires that you FileWrite every parameter you want your EA to recover upon re-loading the terminal.

* Decentralized nodes.

In this case you run several terminals with the same software and they share a combined file.

If one terminal fails this is not a problem because there are more running on the same account.

This requires an even deeper or synchronized level of coding.(as Nodes)

[Stanislav Korotky]

Marco vd Heijden:

Global variables will be lost !

This is incorrect. Global variables are retained between restarts. They are just a simple way of storing data in a special file the terminal maintains for you.

[Marco vd Heijden]

Stanislav Korotky:
This is incorrect. Global variables are retained between restarts. They are just a simple way of storing data in a special file the terminal maintains for you.

Please restart your computer and try again.

Which files are they stored in?

Are you referring to a file on disk ?

or to a virtual memory location ?

It seems to me that Bob is looking for a solution that will work even in case his fuse trips because the dishwasher had an internal short circuit for example.

[Stanislav Korotky]

Marco vd Heijden:

Please restart your computer and try again.

Which files are they stored in?

Are you referring to a file on disk ?

or to a virtual memory location ?

It seems to me that Bob is looking for a solution that will work even in case his fuse trips because the dishwasher had an internal short circuit for example.

I don't have full technical details, except that the file with global variables is MetaTrader's work folder\profiles\gvariables.dat and updates promptly (I don't know exact timing). They exist in memory for quick access and constantly backed up on the disk. The GVs do definitely survive between sessions. You may address your in depth questions to MQ. In case when PC halts unexpectedly you can not guarantee that information will be saved by any means, including file writes suggested by you.

[Biantoro Kunarto]

Marco vd Heijden:

Please restart your computer and try again.

Which files are they stored in?

Are you referring to a file on disk ?

or to a virtual memory location ?

It seems to me that Bob is looking for a solution that will work even in case his fuse trips because the dishwasher had an internal short circuit for example.

You can read this link :

Global variables are kept in the client terminal for 4 weeks since the last access, then they will be deleted automatically. An access to a global variable is not only setting of a new value, but reading of the global variable value, as well.