Non-local object

一、对于non-local object，cppreference是在Initialization#Non-local variables章节进行描述的。

二、在 pabloariasal C++ - Initialization of Static Variables 中，其实已经涵盖了cppreference Initialization#Non-local variables 中的内容

在阅读本文之前，需要直到如下实时:

1、pabloariasal C++ - Initialization of Static Variables # The Two Stages of Static Variable Initialization

As discussed, variables with static storage duration must be initialized once before the program starts and destroyed after execution terminates.

Initialization of static variables happens in two consecutive stages: static and dynamic initialization.

cppreference Initialization#Non-local variables

NOTE: 首先需要搞清楚non-local variable的概念，参见

• Theory\Resource-management\Memory-management\Variable章节

• C-family-language\C++\Language-reference\Basic-concept\Data-model\Object\Storage.md章节

All non-local variables with static storage duration are initialized as part of program startup, before the execution of the main function begins (unless deferred, see below).

All non-local variables with thread-local storage duration are initialized as part of thread launch, sequenced-before the execution of the thread function begins.

For both of these classes of variables, initialization occurs in two distinct stages:

Static initialization

NOTE: static initialization的含义是什么？它是发生在compile-time吗？是的

Dynamic initialization

NOTE:

一、可以看到，dynamic initialization的order是非常复杂的，且存在着unordered，如果program依赖于这个order，则可能导致"static initialization order fiasco(problem)"

关于ordered、unordered，参见C++\Guide\Order。

二、显然，initialization order是建立在translation unit上的一个规则，参见C-and-C++\From-source-code-to-exec\Phases-of-translation\Separate-compilation-model。

其实上述规则可以简单地总结如下:

translation unit之内: ordered

translation unit之间: unordered

上面提及的unordered这是static initialization order fiasco的根源；由于这种unordered是out of control ，因此programmer必须要使用一种可以control的替换方案。

这是解决这类问题的主要思路。

After all static initialization is completed, dynamic initialization of non-local variables occurs in the following situations:

1) Unordered dynamic initialization,

2) Partially-ordered dynamic initialization, (since C++17)

3) Ordered dynamic initialization, which applies to all other non-local variables:

Within a single translation unit, initialization of these variables is always sequenced in exact order their definitions appear in the source code.

NOTE: ordered

Initialization of static variables in different translation units is indeterminately sequenced.

NOTE: unordered

Initialization of thread-local variables in different translation units is unsequenced.

NOTE: unordered

Early dynamic initialization

Deferred dynamic initialization

End

在cppreference Initialization#Notes章节，有这样的描述:

The order of destruction of non-local variables is described in std::exit.