在 Rust 中，如何从第三方库定义或导入 C 结构? [英] In Rust how can I define or import a C struct from a third party library?

问题描述

Rust FFI 指南(http://static.rust-lang.org/doc/master/guide-ffi.html) 很好地演示了如何导入使用由 Rust std::lib 库包装的标准 C 类型的 C 函数，例如 size_t.但是如何将第三方库中定义的 C 数据结构引入 Rust 程序?

The Rust FFI guide (http://static.rust-lang.org/doc/master/guide-ffi.html) nicely demonstrates how to import C functions that use standard C types that are wrapped by the Rust std::lib library, such as size_t. But how do I bring C data structures defined in third party libraries into a Rust program?

我正在使用 libmemcached，它具有以下功能:

I'm working with libmemcached, which has the following function:

memcached_st* memcached_create(memcached_st *ptr)

通常在 C 程序中像这样调用(启动):

which is typically invoked like so in a C program (to kick things off):

#include <libmemcached/memcached.h>
// ...
memcached_st *memc;
memc = memcached_create(NULL);

memcached_st 是一个不透明的 C 结构 - 我如何在 Rust 程序中声明和使用它?以下是我迄今为止失败的尝试:

The memcached_st is an opaque C struct - how do I declare and use that in a Rust program? Here are my failed attempts so far:

use std::libc::*;
use ptr;

#[link(name = "memcached")]
extern {
    struct memcached_st;  // error: unexpected token: `struct`
    memcached_st* memcached_create(memcached_st *ptr);
}

fn main() {
    unsafe {
        let memc = memcached_create(ptr:null());
        println!("{:?}", memc);
    }
}

和

use std::libc::*;
use ptr;

#[link(name = "memcached")]
extern {
    // error: unexpected token: `memcached_st`
    memcached_st* memcached_create(memcached_st *ptr);
}

fn main() {
    unsafe {
        let memc = memcached_create(ptr:null());
        println!("{:?}", memc);
    }
}

推荐答案

使用空结构是一种有效的方法.你几乎明白了，你只是不需要把结构定义放在 extern 块中.此外，您不能在 Rust 源代码中使用 C 代码 - 外部定义必须遵循标准的 Rust 语法.

Using empty structure is a valid approach. You almost got it, you just don't need to put the struct definition in extern block. Also you can't use C code inside Rust sources - extern definitions have to follow standard Rust syntax.

use std::ptr;

struct memcached_st;

#[link(name = "memcached")]
extern {
    fn memcached_create(ptr: *memcached_st) -> *memcached_st;
}

fn main() {
    unsafe {
        let memc = memcached_create(ptr::null());
        println!("{:?}", memc);
    }
}

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