双括号"[[foo()]] type name;"的含义C ++中的语法? [英] Meaning of double bracket "[[foo()]] type name;" syntax in c++?

问题描述

在此文章中，避免虚假共享，显示以下代码以进行对齐:

In this article about avoiding False Sharing, the following code snipped for alignment is presented:

// C++ (using C++0x alignment syntax)
template<typename T>
struct cache_line_storage {
   [[ align(CACHE_LINE_SIZE) ]] T data;
   char pad[ CACHE_LINE_SIZE > sizeof(T)
        ? CACHE_LINE_SIZE - sizeof(T)
        : 1 ];
};

第4行是什么意思?我以前从未见过这种双括号语法.

What is the meaning of line 4? I've never seen this double bracket syntax before.

推荐答案

即属性说明符语法.它是作为一种统一的语法引入的，以访问以前是编译器特定的扩展(现在已标准化).

That is the attribute specifier syntax. It was introduced as a unified syntax to access what were formerly compiler-specific extensions (now some are standardized).

在这种情况下，代码告诉编译器将数据与 CACHE_LINE_SIZE 字节对齐.

In this case the code is telling the compiler to align data to CACHE_LINE_SIZE bytes.

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