Global non-static variable in an unnamed namespace

Question

I cannot find a good explanation of global non-static variables in an unnamed namespace. I avoid global variables as much as I can. In this particular case, I am only interested in behavior from a purely theoretical point of view.

Assume the following code:

In ah

namespace ai {
  class Widget {
    void DoSomething(int param);
  };
}

In a.cc

namespace {
  int x;
  void Helper() {
  }
}

namespace ai {
  void Widget::DoSomething(int param) {
    x = param;
    Helper();
  }
}

• If I created two instances of the same Widget class, would both instances have the same x variable?

• Is the above behavior the same if the class instances are on the same thread against different threads?

• What if the variable x is instead of the built-in type?

• When will the variable x be processed and when will it be destroyed?

• Is there any relation between sizeof (Widget) and such variables?

• What aspects are defined in the C ++ standard, and what not?

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Answer 1

• , x.
• , x.
• , x.
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• , 1-4 .

, static: , .

static int x; 
namespace { 
  void Helper() { 
  } 
}

, static ( /)

Answer 2

     Widget,      x?

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x ?

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- sizeof (Widget) ?

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Answer 3

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++ : ++ faq lite