Does it make any sense to declare a static variable in a class' function where the object is static

Question

Lets say my class lets say I have

static classA myObject;

void classA::update(int elapsed)
{
  static int sumElapsed = 0;
  sumElapsed+= elapsed;

}

It seems that my questions is kind of hard to understand. But if we say that myObject is a singleton of classA. Is there a difference between the local static int sumElapsed and a private member int sumElapsed of the classA, other than the scope in which they can get accessed.

score 3 · Answer 1 · edited May 23 '17 at 11:48

3

Sure. For example in the singleton pattern. There a reference (or pointer) to the static variable is also returned from a static method.

For an example see here: c++ Meyers singleton undefined reference

By the way, if you are interested: Are Singletons really that bad?

edited May 23 '17 at 11:48

Community

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answered Feb 06 '12 at 21:27

Johan Lundberg

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score 0 · Answer 2 · answered Feb 06 '12 at 21:27

0

If you don't want sumElapsed to be overwritten then yes, but it does seem like it would make more sense to have sumElapsed ecapsulated within classA as a static variable.

answered Feb 06 '12 at 21:27

PAULDAWG

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Doesn't having the suMelapsed encapsulated within classA as a none-static variable would have the same effect since classA is static? – DogDog Feb 06 '12 at 21:31
No because I think that is a issue with scope. Static declares that the variable remains in memory. The variable would be overwritten every time since it is being set to 0 in the update function. Should only need to be initialized once. – PAULDAWG Feb 06 '12 at 21:40
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@Apoc But you don't have `sumElapsed` encapsulated. You declare it within `update`. If you also have a class member `classA::sumElapsed`, then the local variable will be hiding it--bad practice. I think I see your confusion--the solution is to declare `sumElapsed` within `classA`, statically, and just use it within the static method as you would any member. The compiler will force the static declaration of `sumElapsed` in this case. – Matt Phillips Feb 06 '12 at 21:44
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That's what I suggested to do, Matt. Thanks for the support. :) – PAULDAWG Feb 06 '12 at 21:57
Ha I was switching back and forth between windows, somehow thought that Apoc's comment was a response to my own answer. Sorry, not trying to horn in on your answer! – Matt Phillips Feb 06 '12 at 22:09

score 0 · Answer 3 · answered Feb 06 '12 at 21:29

Effectively, when you need some sort of a static member in a class template there aren't really good alternatives in the first place. Also, if the members aren't trivial you probably want to put them into a function in the first place to have some level of control over the order of initialization.

In general, be aware that whether you put a static member into a class or into a function, it is still effectively implementing the Singleton anti-pattern!

score 0 · Answer 4 · answered Feb 06 '12 at 21:30

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Of course. If sumElapsed isn't static, it will get overwritten every time the function is called; as it is, it won't be. The fact that classA::update is itself static is irrelevant; just consider if it was a global function (e.g. in C).

answered Feb 06 '12 at 21:30

Matt Phillips

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Made some clarification, I meant that the class A object is static not the function. – DogDog Feb 06 '12 at 21:34

score 0 · Answer 5 · answered Feb 06 '12 at 21:35

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You should use a static class to hold methods that are not associated with a particular object. That being said, use a static class to hold only static members that cannot be instantiated by objects, and shouldn't be overwritten.

answered Feb 06 '12 at 21:35

Ben Sewards

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Does it make any sense to declare a static variable in a class' function where the object is static

5 Answers5