VS 2012 / VC11中的对齐和STL [英] Alignment and the STL in VS 2012/VC11

问题描述

我有一个模糊的记忆STL有对齐结构（例如SIMD向量放在std ::向量）的麻烦，除非你指定一个自定义分配器。

I have a vague memory of the STL having trouble with aligned structs (e.g. SIMD vectors placed in a std::vector), unless you specify a custom allocator.

根据此文档，VS 2012 / VC11已部分支持 c ++ alignment 。这是否意味着VS STL实现现在可以处理对齐的结构，而不提供自定义分配器？

According to this document VS 2012/VC11 has partial support for c++ alignment. Does this mean that the VS STL implementation can handle aligned structs now, without providing a custom allocator?

推荐答案

否。这意味着VC ++编译器支持一种方法来为类型（ __ declspec（align（N））语法指定所需的对齐方式。 VC ++一直支持，它基本上被列为partial，因为我们有一些对齐相关的功能，看起来比说不支持更好。

No. It means that the VC++ compiler supports a method for specifying the required alignment for a type (the __declspec(align(N)) syntax). VC++ has always supported that, and it is basically listed as "partial" because "we have some alignment-related functionality, and it looks better than saying "not supported".

除此之外，我不知道C ++ 11对齐规范中的任何东西，这表明在标准库容器中的SIMD向量是保证工作的C ++ 11对齐基本上只是一个形式化的编译器已经做在这方面（就我所知，如果你能证明我错了，我会很乐意的）。

Apart from that, I'm not aware of anything in the C++11 alignment specification which indicates that SIMD vectors in a standard library container is guaranteed to work. C++11 alignment is basically just a formalization of what compilers already did, in this regard (as far as I know. I'd love if you could prove me wrong).

SIMD向量是标准调用的over-aligned types （见关于扩展对齐的部分）这意味着基本上我们保证什么，这完全取决于编译器如何/如果他们处理这种类型。

SIMD vectors are what the standard calls "over-aligned types" (see the part about "extended alignment"). What that means is basically "we guarantee nothing, and it's entirely up to the compiler how/if they handle such types.

换句话说，实现C ++ 11的这一部分不一定会改变SIMD对象的处理方式。

In other words, implementing this part of C++11 would not necessarily change how SIMD objects are handled.

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