global variable or function?

[TheSaint]

In most cases (with programming languages and/or scripting languages) it's to do with memory management, in which you specify the lifespan of how long a block of memory is reserved for the executable by the system. On MDN the memory life cycle hits the nail on the head.

Note: If you just declare all variables in Global then it's no different to using Dim, which wasn't the point Valik was trying to make in the article he posted.

Last part first - That may be so to a point, but he was also saying don't use Dim at all, which is the part I took on board, with the rest at that stage of my learning, just implanted in my brain for later cogitation as I gather more input.

I hear what you are saying, and I have read the reference to memory before, but I guess I'm after a real world scenario, where it actually makes a difference to my experience or those who use my programs. In other words, what is the penalty in real measurable terms?

[guinness]

I don't get how else I can explain it, especially as you want a real world example for something that is just good coding practice and house keeping. If it's just yourself who uses your application then of course you have no obligation to worry about how much memory you use on a user's system, but then not everyone has a lot of memory, especially for those of us who have Visual Studio 2013 and Android Studio running in the background.

There is only a finite amount of memory on a user's system, so if every developer adopted the "I don't really care" approach, then we would all be in serious trouble.

Edited January 19, 2015 by guinness

[Guest]

Good. Hopefully the help file is clear about this.

 

Yes, the examples are clear.

But I was put the Example 2 as Example 1, and Example 1 as Example 2.

Because Example 2 is more clear then Example 1

Edited January 19, 2015 by Guest

[TheSaint]

There is only a finite amount of memory on a user's system, so if every developer adopted the "I don't really care" approach, then we would all be in serious trouble.

I wouldn't class myself as someone who doesn't care, and I'm always willing to learn, and that's the whole point of me joining this conversation.

As always, I try to take a logical approach and weigh up as many factors as I can think of, sometimes ones that others don't.

I have immense respect and admiration for your coding skill, organizational and programming ability, and I always take on board things you say in those areas for sure. I don't necessarily adopt what you say though, as I use my mind too.

For instance, here are a few questions slash observations.

[1] What difference is there when it comes to memory use, between a variable that is declared as Global and one that is declared as Local, if they have exactly the same content?

[2] If I have a thousand variables that are all assigned one word, or a single variable assigned a thousand words, what is the difference?

[3] How many variables does it take to have a significant impact on memory use? No doubt this is a trick question, because a variable can contain anything from a single letter to a huge number of characters, etc.

[4] I try to be cognizant of good practice, but sometimes the real world intrudes. Is it good practice to expend a significant portion of brain power on keeping tabs on the scope for every variable, and being diligent with their use? Does doing so increase the margin for error and the later necessary bug fixes, and harder troubleshooting?

[5] Have any of you ever created something to measure the memory use of variables?

[6] It seems to me, the more power and things our computers can do, the more we use them for multiple simultaneous tasks. I know I can do it too, but I refrain from anything while doing something memory intensive (CD burning, Video editing, etc). I know from hard earned experience, that it is not a good idea ... errors happen even though they often don't get detected.

[czardas]

[3] How many variables does it take to have a significant impact on memory use? No doubt this is a trick question, because a variable can contain anything from a single letter to a huge number of characters, etc.

 

The answer to this is very easy. It only takes one. I tested this. The variable in question had an integer value of zero. I admit that the variable name was very very very long, but memory went awol. This also gives clues to question [2].

[1] What difference is there when it comes to memory use, between a variable that is declared as Global and one that is declared as Local, if they have exactly the same content?

 

This should be obvious. Returning from a function releases memory.

[4] I try to be cognizant of good practice, but sometimes the real world intrudes. Is it good practice to expend a significant portion of brain power on keeping tabs on the scope for every variable, and being diligent with their use? Does doing so increase the margin for error and the later necessary bug fixes, and harder troubleshooting?

 

Quite the contrary. Avoiding global variables and using more fuctions takes care of ever having to worry about scope.

Edited January 19, 2015 by czardas

[TheSaint]

The answer to this is very easy. It only takes one. I tested this. The variable in question had an integer value of zero. I admit that the variable name was very very very long, but memory went awol. This also gives clues to question [2].

It is probably more correct to say - it can take only one significant variable to cause an impact.

Further to my other questions/observations.

[7] I can remember at time, when it was important to clear a variable after it was no longer needed ($var = '').

Do you think that is still important? Should we still do it?

[8] How much memory space is taken up by declaring an empty variable (Global or Local)?

Edited January 19, 2015 by TheSaint

[guinness]

TheSaint,

I will try my best to answer your questions. Let me know if 

1. If the variable is local then once out of scope e.g. end of a function, the memory location is marked as free and available for anyone else to use and by anyone else, I mean those applications which are running on the system. By having it global, you're effectively reserving that memory space for the entire duration of the applications execution.
2. Well you would use an array and not hard-code a thousand variables. So the difference is down to readability and script maintenance. This is a little off-topic I feel.
3. It's not about the amount per say, but if you have a total of 1000 variables (which hold a variant in AutoIt) and you only use 10 as truly global, then you're effectively reserving memory space for nothing, when it's not required.
4. Actually it's easier to code when you use variables in the lowest possible scope, because you don't have to keep scrolling back up to see if you declared the variable or not. As generally speaking if you adopt this approach of "lowest possible scope" then the variable should be in plain view of where you're using it. So actually having all variables at the top of the script (remember this is where global variables should be placed and not inside function) is a lot harder to follow as your code grows overtime i.e. prone to more errors.
5. Yes. Though it's not for public use, sorry.
6. Isn't video editing more CPU intensive?

[czardas]

[7] I can remember at time, when it was important to clear a variable after it was no longer needed ($var = '').

Do you think that is still important? Should we still do it?

 

This depends on the amount of memory the variable takes up and how long it is needed. Yes it is a good idea for large arrays and the likes. It would be a little too extreme to do this for every variable and pointless if done immediately prior to a function return.

Edited January 19, 2015 by czardas

[guinness]

It is probably more correct to say - it can take only one significant variable to cause an impact.

Further to my other questions/observations.

[7] I can remember at time, when it was important to clear a variable after it was no longer needed ($var = '').

Do you think that is still important? Should we still do it?

[8] How much memory space is taken up by declaring an empty variable (Global or Local)?

1. If the variable is local then no, it will be destroyed when the function is returned from. If global, then I guess it's a case of do you want to remove what the variable is point to in memory.
2. AutoIt doesn't store datatypes like other languages, but an empty space is a single character, which is a byte plus the null terminator, so 2 bytes.

I think we, czardas and I have answered your questions.

[guinness]

Yes, the examples are clear.

But I was put the Example 2 as Example 1, and Example 1 as Example 2.

Because Example 2 is more clear then Example 1

I am happy with the help file page as it is.

[czardas]

I think this topic has covered so much ground that perhaps it would be better if it were moved to Dev Chat.

[guinness]

I think this topic has covered so much ground that perhaps it would be better if it were moved to Dev Chat.

I whole heartedly agree.

[Melba23]

Someone called?

M23

[Guest]

 

1. If the variable is local then no, it will be destroyed when the function is returned from. If global, then I guess it's a case of do you want to remove what the variable is point to in memory.

 

Even if it is Local Static ?

SomeFunc()

Func SomeFunc()
    Local Static $aArray[10000000]
EndFunc

; It will take 44MB from the memory even if SomeFunc() Exited.
MsgBox(0,'','')

 

I think you're wrong here.

 

I think we should be careful with Local Static. When it comes to memory use, it is exactly like normal global

Edited January 19, 2015 by Guest

[guinness]

gil900,

Of course not, but I was only asked to explain about Local and Global. The difference between Local Static and Global, is if the function is never called then that 44MB (for example) will never be reserved, whereas if global it would have been.

[TheSaint]

I'm still taking it all in, but I will respond to 6 and 4.

6. Yes, that's what I was saying. Burning is too, though these days we have the Burnproof thing to help keep the buffer full. What I was trying to say, was that I would never do both of those processes at the same time or other similar memory intensive ones.

4. I never declare Global other than at the top of my scripts (and never in Functions), except perhaps where I'm testing something I will later relocate to top or change to Local ... never in the finished script. For the rest, I don't see it that way. I declare all variables as Global at the top of my script (except Locals). I even have a program to do that for me. I never have to consider scope, except when I want it Local. I never look back to see if I've declared it, it is a given ... no expenditure of thought needed. Mistakes happen either way. So from my perspective, your way is harder.

[BrewManNH]

You don't make them static if you're planning on destroying them when the function ends.

[Guest]

 

 

gil900,

Of course not, but I was only asked to explain about Local and Global. The difference between Local Static and Global, is if the function is never called then that 44MB (for example) will never be reserved, whereas if global it would have been.

Ok.
But I think there are many who consider Local Static as part in Local

because it sounds very logical. So I think you take it in your answer

Edited January 19, 2015 by Guest

[TheSaint]

@Melba23 - Go ahead and relocate, I will wait.

[BrewManNH]

Local Static IS local, it can only be seen inside the function it's declared in. It just doesn't lose it's contents when the function ends.