全局变量的初始化是否与 function 内部变量 static 的初始化相同

Question

I'm trying to figure out all different kinds of initialization in C++. Now I'm reading this link: https://en.cppreference.com/w/cpp/language/zero_initialization

In the example of this link, we have such a piece of code:

std::string s; // zero-initialized to indeterminate value
               // then default-initialized to ""

As my understanding, the initialization of the global variable is as below:

When we compile the code, the s is zero-initialized, it is put at the .bss segment of the binary file. When we run the binary file (meaning that the kernel is starting to load the binary file into RAM), the s is default-initialized to the empty string "" .

Now, we define a function as below:

void func()
{
    static std::string s;
}

If we call the function first time, the s will be initialized, this is for sure. But is it still initialized with two methods: first zero initialization, then default initialization, just like the first s ?

BTW, I'm working on Ubuntu, X86_64 architecture with the compiler GCC 7.5. If my question is not standardized by C++, you could tell me in the comment and I'll close this question.

Answer 1

But is it still initialized with two methods: first zero initialization, then default initialization, just like the first s?

Assuming, the "as-if"-rule effectively forces the compiler to consider the existence of this variable, yes. Excerpts from the standard:

Zero initialization is performed in the following situations:

1. For every named variable with static or thread-local storage duration that is not subject to constant initialization, before any other initialization.

Default initialization is performed in three situations:

1. when a variable with automatic, static, or thread-local storage duration is declared with no initializer;

As molbdnilo said within the comments, you should avoid thinking in terms of binary files, kernel and segments here totally if you are only interested in the behavior the standard claims.