如何创建一个Rust回调函数以传递给FFI函数？

Question

这就是C API的样子。

void mosquitto_connect_callback_set(struct mosquitto *mosq, void (*on_connect)(struct mosquitto *, void *, int));

rust-bindgen已经为我生成了这个

pub fn mosquitto_connect_callback_set(
    mosq: *mut Struct_mosquitto,
    on_connect: ::std::option::Option<
        extern "C" fn(
            arg1: *mut Struct_mosquitto,
            arg2: *mut ::libc::c_void,
            arg3: ::libc::c_int,
        ) -> (),
    >,
)

如何创建一个Rust回调函数以传递到上述Rust绑定中的on_connect参数？

Answer 1

http://doc.rust-lang.org/stable/book/，第一版，有一个关于FFI的章节，名为C代码对锈蚀函数的回调。

下面的例子是

extern "C" fn callback(a: i32) {
    println!("I'm called from C with value {0}", a);
}

#[link(name = "extlib")]
extern "C" {
    fn register_callback(cb: extern "C" fn(i32)) -> i32;
    fn trigger_callback();
}

fn main() {
    unsafe {
        register_callback(callback);
        trigger_callback(); // Triggers the callback
    }
}

对于您的具体情况，您已经知道了您需要的特定类型的函数：

extern "C" fn mycallback(
    arg1: *mut Struct_mosquitto,
    arg2: *mut ::libc::c_void,
    arg3: ::libc::c_int,
) -> () {
    println!("I'm in Rust!");
}

然后把它当作

mosquitto_connect_callback_set(mosq, Some(mycallback));