如何将结构与指定的字节边界对齐? [英] How can I align a struct to a specified byte boundary?

问题描述

我需要将结构与 Rust 中的 16 字节边界对齐.似乎可以通过 repr 属性，但它不支持这个确切的用例.

I need to align a struct to a 16 byte boundary in Rust. It seems possible to give hints about alignment through the repr attribute, but it doesn't support this exact use case.

我试图实现的功能测试是一个类型 Foo 使得

A functional test of what I'm trying to achieve is a type Foo such that

assert_eq!(mem::align_of::<Foo>(), 16);

或者，一个结构体 Bar 带有一个字段 baz 使得

or alternatively, a struct Bar with a field baz such that

println!("{:p}", Bar::new().baz);

总是打印一个能被 16 整除的数字.

always prints a number divisible by 16.

这在 Rust 中目前是否可行?有什么解决办法吗?

Is this currently possible in Rust? Are there any work-arounds?

推荐答案

huon 的回答很好，但是已经过时了.

huon's answer is good, but it's out of date.

从 Rust 1.25.0 开始，您现在可以将类型与 N 对齐 字节使用属性 #[repr(align(N))].它记录在 参考的类型布局部分.请注意，对齐必须是 2 的幂，您不能混合 align 和 packed 表示，并且对齐类型可能会为类型添加额外的填充.这是如何使用该功能的示例:

As of Rust 1.25.0, you may now align a type to N bytes using the attribute #[repr(align(N))]. It is documented under the reference's Type Layout section. Note that the alignment must be a power of 2, you may not mix align and packed representations, and aligning a type may add extra padding to the type. Here's an example of how to use the feature:

#[repr(align(64))]
struct S(u8);

fn main() {
    println!("size of S: {}", std::mem::size_of::<S>());
    println!("align of S: {}", std::mem::align_of::<S>());
}

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