c++ - 静态变量 : Construction happens after usage

Question

我正在 Visual Studio 2013 的控制台应用程序中进行一些测试。涉及静态变量，我看到一些奇怪的行为。主要问题是 GenericFactory 模板类的静态 Printer 成员是在我使用它之后构造的(在其 Register函数)!

关于全局/静态变量和初始化顺序的规则非常复杂，所以有人可以帮我理解这里出了什么问题吗？代码如下。

ma​​in.cpp:

#include <iostream>

int main()
{
   std::cout << "Main Function\n";
}

通用工厂.hpp:

#pragma once

#include <functional>
#include <map>
#include <memory>
#include <iostream>

class Printer
{
public:
   Printer()
   {
      std::cout << "Printer class created\n";
   }

   void Stuff()
   {
      std::cout << "Printer Stuff, Address " << (int)this << "\n";
   }
};

template<typename Key>
class GenericFactory
{
public:

   static Key const& Register(Key const& key)
   {
      GenericFactory::s_printer.Stuff();
      std::cout << "Registered: " << key << "\n";
      return key;
   }

private:
   static Printer s_printer;
};

template<typename Key>
Printer GenericFactory<Key>::s_printer;

StringFactory.hpp:

#pragma once

#include <string>
#include "GenericFactory.hpp"

using StringFactory = GenericFactory<int>;

test1.cpp:

#include "StringFactory.hpp"

namespace Other
{
   static auto key = StringFactory::Register(100);
}

test2.cpp:

#include "StringFactory.hpp"

namespace Other
{
   static auto key = StringFactory::Register(200);
}

运行上述应用程序后得到的输出:

Printer Stuff, Address 3422532
Registered: 100
Printer class created
Printer Stuff, Address 3422532
Registered: 200
Main Function

请注意，"Printer Stuff, ..." 在 "Printer class created" 之前打印。我在这里要疯了吗？

Answer 1

您假设全局变量的构造顺序。这不是一个好方法。尝试将其更改为类似的东西(不是最干净的，但说明了这一点):

template<typename Key>
class GenericFactory
{
   static Printer& printer()
   {
       static Printer s_printer;
       return s_Printer;
   }
public:


   Key const& Register(Key const& key) // removed static here.
   {
      printer().Stuff();
      std::cout << "Registered: " << key << "\n";
      return key;
   }

};

编辑:

这是我用于不需要多线程双锁保护的单例的典型模式:

#include <memory>

class MySingletonClass
{
public:
  static MySingletonClass* instance()
  {
    static std::unique_ptr<MySingletonClass> ptr(new MySingletonClass);
    return ptr.get();
  }

  // Public functions here

private:
  friend struct std::default_delete<MySingletonClass>;
  // Hide these to avoid unintentional copy
  MySingletonClass() {}
  ~MySingletonClass() {}
  MySingletonClass(const MySingletonClass&) {}
  MySingletonClass& operator= (const MySingletonClass&) { return *this; }
};

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