静态变量的地址 [英] Address of a static variable

问题描述

我想做一个简单的类来唯一的ID转换。我正在考虑添加一个静态方法：

I am trying to do a simple class to unique ID conversion. I am thinking about adding a static method:

class A {
  static int const *GetId() {
    static int const id;
    return &id;
  }
};

每个类将由唯一的 int const * 。这是保证工作吗？返回的指针真的是唯一的吗？有没有更好的更简单的解决方案？

Each class would then be identified by unique int const *. Is this guaranteed to work? Will the returned pointer really be unique? Is there any better simpler solution?

我也想过指向 std :: type_info ：

class A {
  static std::type_info const *GetId() {
    return &typeid(A);
  }
};

这更好吗？

修改：

我不需要使用ID进行序列化。我只想识别一小组基类，我想要一些类的所有子类具有相同的id

I don't need to use the id for serialization. I only want to identify a small set of base classes and I want all subclasses of some class to have the same id

推荐答案

As我注意到至少MSVC 2008或2010优化静态变量，以便下面的 GetId 函数返回相同的地址，即使对于不同的类。

As I have noticed at least MSVC 2008 or 2010 optimizes the static variable, so that the following GetId function returns same address even for different classes.

static int const *GetId() {
    static const int i = 0;
    return &i;
}

因此，未初始化的常量静态变量的地址可能不能用于识别。最简单的解决方法是删除 const ：

Therefore address of uninitialized constant static variable may not be used for identification. The simplest fix is to just remove const:

static int *GetId() {
    static int i;
    return &i;
}

另一个生成ID的解决方案似乎有效，函数作为计数器：

Another solution to generate IDs, that seems to work, is to use a global function as a counter:

int Counter() {
    static int i = 0;
    return i++;
}

然后在要识别的类中定义以下方法：

And then define the following method in the classes to be identified:

static int GetId() {
    static const int i = Counter();
    return i;
}

由于要定义的方法总是相同的，基类：

As the method to be defined is always the same, it may be put to a base class:

template<typename Derived>
struct Identified {
    static int GetId() {
        static const int i = Counter();
        return i;
    }
};

然后使用奇怪的重复模式：

And then use a curiously recurring pattern:

class A: public Identified<A> {
    // ...
};

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