persistent variables in functions ?

[KAX]

Hello to the AutoIt experts.

Is it possible to define persistent variables inside a function?

The variable should keep its value for following function calls (similar C static vars).

Example:

Func DoIt()

Dim $count = 0

$count += 1

...

EndFunc

[PsaltyDS]

Hello to the AutoIt experts.

Is it possible to define persistent variables inside a function?

The variable should keep its value for following function calls (similar C static vars).

Example:

Func DoIt()

Dim $count = 0

$count += 1

...

EndFunc

Constants are declared with the keyword Const.

Hmm... didn't think to check that a Const variable would remain in Global context when declared in a function. Have to test that... but it should work:

Global Const $FuncTime = @Hour & @Min

I wonder what happens when you run that function a second time though...

Edited July 14, 2006 by PsaltyDS

[MHz]

Welcome,

Use Global $variable.

A Global variable is seen by the whole script and is not destroyed if used within a function.

Edit:

Or stated more correct...is not destroyed when exiting a function.

Edited July 14, 2006 by MHz

[KAX]

Welcome,

Use Global $variable.

A Global variable is seen by the whole script and is not destroyed if used within a function.

Edit:

Or stated more correct...is not destroyed when exiting a function.

You are right, global will work. But when the program grows and grows you have to be very sure which global to use. In other words : global namespace pollution.

Thank you.

[jvanegmond]

I actually like to Global everything. And when my script is done, i might change it back to Dim's or Constants. Is this a bad thing to do?

[MHz]

I actually like to Global everything. And when my script is done, i might change it back to Dim's or Constants. Is this a bad thing to do?

On a small script, you maybe able to get away with that plan. But once you create a script that goes into hundreds or especially thousands of lines of code, then that would turn into a major disaster indeed. Number of Global varaibles does tend to increase with more lines of code, and does become somewhat alot to manage after awhile. That can become the so-called "Global variable pollution" problems that KAX tends to relate to.

I could not survive without Local variables in Functions to help prevent accidental Global variable destruction.

[jvanegmond]

Its funny when that happens, or can also be very annoying. Because you really have no idea what's going on.

I often have this problem when calling $x a global variable and then calling it in for loops (For $x = )

Edited July 14, 2006 by Manadar

[ivan]

I'm kind of using a rule of thumb now...

I usually keep a const region at the top of the script for values that will not change while the script runs, say paths, urls, username, whatever one can think of.

I also declare my global vars and global array vars in 2 separate regions at the top of the script, regardless of whether or not they are initialized at a later stage.

All the rest are local in the scope of functions that normally return a value which helps me in testing and debugging.

Having said all that, is anyone aware of limitation to the amount of global variables, arrays and constants a script can hold?

IVAN

[KAX]

Thanks all for your replies.

It seem there is no builtin support for persistent variables.

So I decided to use naming rules to distinguish the used globals.

I. e.: %bIsInitialised_Func1

means the variable 'bIsInitialised' is reserved for function 'Func1'.

What do you thing about this?

[PsaltyDS]

Thanks all for your replies.

It seem there is no builtin support for persistent variables.

So I decided to use naming rules to distinguish the used globals.

I. e.: %bIsInitialised_Func1

means the variable 'bIsInitialised' is reserved for function 'Func1'.

What do you thing about this?

Huh?

Whadd'ya mean by "no builtin support for persistent variables"?

Using the Global keyword is your basic answer, plus the Const keyword in special circumstances where you don't the value to be changeable. Please post a definition of what you want "persistent variables" to do. If you can, a short snippet of code demonstarting it would be very helpful.

[/dev/null]

I. e.: %bIsInitialised_Func1

means the variable 'bIsInitialised' is reserved for function 'Func1'.

What do you thing about this?

well, besides that % bIsInitialised_Func1 is not a variable, you can do that.

Cheers

Kurt

[Valik]

Huh?

Whadd'ya mean by "no builtin support for persistent variables"?

Using the Global keyword is your basic answer, plus the Const keyword in special circumstances where you don't the value to be changeable. Please post a definition of what you want "persistent variables" to do. If you can, a short snippet of code demonstarting it would be very helpful.

The OP is asking for a variable that is local to a function but the value stored in it persists across calls to the function. The equivalent to the static keyword in C\C++. The simplest way to think of it is access to the variable is the same as "Local" but the storage of the data in the variable is the same as "Global". An example would be:

Func Increment()
     Persistent $i = 0
     $i += 1
     Return $i      
EndFunc

MsgBox(4096, "", Increment()); Returns 1
MsgBox(4096, "", Increment()); Returns 2
; MsgBox(4096, "", $i); Error, $i is not in scope

Of course, this is not supported in AutoIt.

Edit: Fixed minor mistake.

Edited July 22, 2006 by Valik

[PsaltyDS]

The OP is asking for a variable that is local to a function but the value stored in it persists across calls to the function. The equivalent to the static keyword in C\C++. The simplest way to think of it is access to the variable is the same as "Local" but the storage of the data in the variable is the same as "Global". An example would be:

Func Increment()
     Persistent $i = 0
     $i += 1
     Return $i      
EndFunc

MsgBox(4096, "", Increment()); Returns 1
MsgBox(4096, "", Increment()); Returns 2
; MsgBox(4096, "", $i); Error, $i is not in scope

Of course, this is not supported in AutoIt.

Edit: Fixed minor mistake.

My appologies for not testing this before asking, but I don't keep Windows machines around anymore, so it will have to wait for Monday...but,

Would this work?

Func Increment()
     If Not IsDeclared("Increment_i") Then Global $Increment_i = 0
     $Increment_i += 1
     Return $Increment_i        
EndFunc

MsgBox(4096, "", Increment()); Returns 1
MsgBox(4096, "", Increment()); Returns 2
; MsgBox(4096, "", $i); Error, $i is not in scope

[Valik]

My appologies for not testing this before asking, but I don't keep Windows machines around anymore, so it will have to wait for Monday...but,

Would this work?

Func Increment()
     If Not IsDeclared("Increment_i") Then Global $Increment_i = 0
     $Increment_i += 1
     Return $Increment_i        
EndFunc

MsgBox(4096, "", Increment()); Returns 1
MsgBox(4096, "", Increment()); Returns 2
; MsgBox(4096, "", $i); Error, $i is not in scope

First, don't ever use IsDeclared() and then use the variable directly. If you'r using IsDeclared(), you must be using Assign() and Eval(), otherwise you have a design issue. Second, using Global from inside functions is bad style.

And to answer your question, no, $Increment_i is still global. It's not possible to create static/persistent variables with AutoIt. Variables are either at the global scope where they live for the entire lifetime of the script and can be accessed from anywhere or they are local to a function, can only be accessed in that function and are destroyed when that function returns.

[KAX]

Thank you Valik for your good explanations.

[PsaltyDS]

First, don't ever use IsDeclared() and then use the variable directly. If you'r using IsDeclared(), you must be using Assign() and Eval(), otherwise you have a design issue. Second, using Global from inside functions is bad style.

And to answer your question, no, $Increment_i is still global. It's not possible to create static/persistent variables with AutoIt. Variables are either at the global scope where they live for the entire lifetime of the script and can be accessed from anywhere or they are local to a function, can only be accessed in that function and are destroyed when that function returns.

Thanks for the correction on using Assign(), I should have known that as I've used that technique to check on a $LogFile being set for the function before doing _FileWriteLog($LogFile, "etc...."). I see that the variable produced is Global and not strictly static/persistent within the function, but other than the fact that other fuctions can see the variable (maybe bad if it's a password, for example), I think it gets the same thing done. By prepending the function name (which has to be unique) to the Global variable's name you get a unique Global variable for the exclusive use of that function.

Seems that would be handy if you want to have required Global variables made available for your UDF without the script having to set it up as a precondition for using the UDF.

Func Increment()
     If Not IsDeclared("Increment_i") Then Assign(Increment_i, 0, 2); 2=Global
     $Increment_i += 1
     Return $Increment_i        
EndFunc

MsgBox(4096, "", Increment()); Returns 1
MsgBox(4096, "", Increment()); Returns 2

I guess another way to look at it would be a re-think of the function to require the script calling the function to provide a ByRef Global in the parameters. That puts the responsibility on the calling script to preserve it between calls to the function:

Global $AnyVar = 0

While 1
     Increment($AnyVar)
     MsgBox(4096, "", Increment()); Returns 1
Wend

Func Increment(ByRef $i)
     $i += 1
     Return $i
EndFunc

This has been very informative, thanks again!