带有位域的 C 风格结构如何在 Rust #[repr(C)] 结构中表示? [英] How does a C-style struct with a bitfield get represented in a Rust #[repr(C)] struct?

问题描述

我有一个 C 结构定义为:

I have a C struct defined as:

struct my_c_s {
    u_char          *ptr;
    unsigned        flag_a:1;
    unsigned        flag_b:1;
    int             some_num;
}

flag_a 和 flag_b 将如何表示?

#[repr(C)]
pub struct my_rust_s {
    pub ptr: *const u_char,
    //pub flag_a: ?,
    //pub flag_b: ?,
    pub some_num: ::libc::c_int,
}

我可以将它们声明为 bools 吗? 或者整个事情是否需要某种具有单个字段的位集，然后我将它们位屏蔽掉?

Can I declare them as bools? Or does that whole thing need to be some sort of set of bits with a single field, and then I bitmask them out?

例如pub flag_bits: ::libc::c_uint,

推荐答案

不，你不能.

有关于支持位域的一个悬而未决的问题，这似乎没有要活跃.在问题中，@retep998 解释了如何在 winapi<中处理位域/代码>.如果您需要在 C 接口中处理位域，这可能会有所帮助.

There is an open issue about supporting bitfields, which doesn't seem to be active. In the issue, @retep998 explains how bitfields are handled in winapi. That might be helpful if you need to handle bitfields in C interface.

OP 似乎针对 C 互操作，但如果您只需要位域功能，有几种解决方案.

OP seems to aim at C interoperation, but if you just need bitfields functionality, there are several solutions.

• 您应该始终考虑简单的冗余解决方案:避免位字段并让字段自然对齐.
• bitfield，根据 评论 -- 我不知道那个，但它似乎提供了等效的 C 位域.
• bitflags.这似乎适用于基于位的标志，在 C 中通常表示为 enum.
• #[repr(packed)] 如果您只想在某种程度上打包字段，而忽略对齐.字段仍将与字节边界对齐.
• bit-vec 如果您需要同构的位数组.

• You should always consider simple redundant solution: avoid bitfields and let fields align naturally.
• bitfield, according to the comment -- I didn't know that, but it seems to provide C bitfields equivalent.
• bitflags. This seems suitable for bit-based flags, which typically represented as enum in C.
• #[repr(packed)] if you just want to pack fields to some degree, ignoring alignment. The fields will still be aligned to byte boundary.
• bit-vec if you need homogenious arrays of bits.

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