在对象为静态的类的函数中声明静态变量是否有意义？

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.

Answer 1

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

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

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

Answer 2

如果您不希望覆盖sumElapsed，则可以，但是，将sumElapsed作为静态变量封装在classA中似乎更有意义。

Answer 3

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 !

Answer 4

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 (eg in C).

Answer 5

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.