是否保证初始化顺序 [英] Is initialization order guaranteed

问题描述

我正在使用类似于以下代码部分的内容进行一些初始化。我知道 p< T> :: i _ 的初始化是无序的。我相信 h 是有序的，所以我应该能够推断出它的初始化顺序。鉴于 p h 的定义之前包括code>，是否可以保证 p< T> :: i _ 将在 h 之前初始化？

I am using something like the following sections of code to do some initialization. I know that the initialization of p<T>::i_ is unordered. I believe that h is ordered, so I should be able to reason about the order that it is initialized in. Given that the header for p is included before the definition of h, is there any guarantee that p<T>::i_ will be initialized before h?

struct helper
{
   template <typename T>
   helper(const T&, int i)
   {
      p<T>::i_::push_back(i);
   }
};
static helper h;

下面定义了类p。

template <typename T>
struct p
{
   static std::vector<int> i_;
};
template <typename T>
std::vector<int> p<T>::i_;

推荐答案

具有静态存储持续时间的对象的初始化顺序为

The order of initialization of objects with static storage duration is undefined across translation units, and sequential within each translation unit.

在您的特殊情况下，情况更加复杂，因为具有静态存储的对象之一是对象的静态成员。模板类。实际上，这意味着访问成员 p< T> :: i _ 的每个翻译单元将创建符号，并添加适当的初始化代码。稍后，链接器将选择其中一个实例并将其保留。即使看起来之前 h 中定义了 p< T> :: i _ 您的翻译单元，您不知道链接器将保留哪个 p< T> :: i _ 实例，并且该实例可能在另一个翻译单元中，并且

In your particular case things are more complicated, since one of the objects with static storage is a static member of a template class. What that means in a practical way is that each translation unit that accesses the member p<T>::i_ will create the symbol, and add the appropriate initialization code. Later the linker will pick one of the instances and keep it. Even if it looks like p<T>::i_ is defined before h in your translation unit, you don't know which instance of p<T>::i_ will be kept by the linker, and that might be one in a different translation unit and thus the order is not guaranteed.

通常，拥有全局对象是一个坏主意，我建议您尝试在没有这些全局对象的情况下重新设计程序。

In general it is a bad idea to have global objects, I would suggest that you try to redesign your program without those globals.

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