C ++ 20之前和之后std :: atomic的初始化 [英] Initialization of std::atomic before and after C++20

问题描述

请考虑以下两行代码:

std::atomic_flag a { };                // Since C++20
std::atomic_flag a = ATOMIC_FLAG_INIT; // Until C++20

在C ++ 20中，第一行将 a 初始化为清除状态，但是如果我在C ++ 17中使用它，则 a 将被初始化为未指定状态.第二行在C ++ 20中已弃用，但在C ++ 17中，它将 a 初始化为clear状态.如何在代码中同时包含它们?我想我应该使用一个宏，但是那个宏到底是什么?并能用于所有其他 std :: atomic< T> 类型的初始化吗?

In C++20, the first line initializes a to the clear state, but if I use that in C++17, a will be initialized to an unspecified state. The second line is deprecated in C++20, but in C++ 17, it initializes a to the clear state. How can I have them both in a code? I guess I should use a macro, but what is that macro exactly? And does it work for the initialization of all the other std::atomic<T> types?

推荐答案

基于@chris注释，我认为以下代码可以完成这项工作:

Based on @chris comment, I think the following code will do the job:

#if __has_cpp_attribute(__cpp_lib_atomic_value_initialization)
std::atomic_flag a { };
#else
std::atomic_flag a = ATOMIC_FLAG_INIT;
#endif

所需的宏在< memory> ，< atomic> 和< version> 头文件之一中定义.我当然不想写已经被弃用的东西(即允许使用，但由于某些原因而劝阻).

The required macros are defined in either one of <memory>, <atomic>, and <version> header files. I certainly don't want to write something that is already deprecated (ie, the use is allowed, but discouraged for some reason).

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