跨平台C库Rust包装器中Vec<u32>转Vec<u64>/Vec<std::os::raw::c_ulong>的非遍历转换方法问询

Great question—this is a common pain point when writing cross-platform Rust bindings for C libraries, where types like size_t vary between Windows (32-bit) and Linux (64-bit). Let’s break down the best approaches for your scenario:

Why You Can’t Avoid Traversal Entirely (On Linux) #

First, let’s get the hard truth out of the way: on Linux, bindings::size_t is an alias for u64, which is twice the size of u32. Since Vec<u32> and Vec<u64> have fundamentally different memory layouts (each element takes up 4 vs 8 bytes), there’s no way to convert between them without iterating over each element to perform the widening conversion. Your current map approach is actually the safe, idiomatic way to do this—though we can tweak it for a bit more brevity:

#[cfg(unix)]
fn convert_pages(pages: Vec<u32>) -> Vec<bindings::size_t> {
    // Use into_iter() to consume the original Vec directly, avoiding reference overhead
    pages.into_iter().map(|p| p as bindings::size_t).collect()
}

Optimizing for Windows (No Traversal Needed) #

On Windows, bindings::size_t is an alias for u32—so Vec<u32> and Vec<bindings::size_t> are essentially the same type under the hood (same memory layout, element size, and alignment). In this case, we can safely use std::mem::transmute to convert the Vec without any iteration:

#[cfg(windows)]
fn convert_pages(pages: Vec<u32>) -> Vec<bindings::size_t> {
    // Safe because bindings::size_t == u32 on Windows; memory layouts match exactly
    unsafe { std::mem::transmute(pages) }
}

A quick note on safety here: this is only safe if you’re certain bindings::size_t is a direct alias for u32 on Windows. Bindgen-generated bindings will follow this convention, but it’s worth double-checking your bindings to be sure.

Putting It All Together #

You can combine these platform-specific implementations into a single function using Rust’s conditional compilation:

fn convert_pages(pages: Vec<u32>) -> Vec<bindings::size_t> {
    #[cfg(windows)]
    {
        unsafe { std::mem::transmute(pages) }
    }
    #[cfg(unix)]
    {
        pages.into_iter().map(|p| p as bindings::size_t).collect()
    }
}

This gives you the best of both worlds: zero-overhead conversion on Windows, and safe, idiomatic conversion on Linux.

内容的提问来源于stack exchange，提问作者Christian Schmitt