Rust(unsafe) 结构体转指针通过LPARAM / usize参数传递

struct_convert_to_usize.rs

struct InOutData {
    pid: u32,   // in
    hwnd: HWND  // out
}

unsafe extern "system" fn callback(hwnd: HWND, lparam: LPARAM) -> BOOL {
    let s: &mut InOutData = mem::transmute(lparam);  // LPARAM转回结构体指针
    if ((*s).pid == GetWindowThreadProcessId(hwnd, Some(ptr::null_mut()))) {
        (*s).hwnd = hwnd;
        return false.into();
    }
    return true.into();
}

fn sender() {
    let mut parm = InOutData {0x1234567A, HWND(0)};
    unsafe { // 将结构体指针转为LPARAM 或者 usize，两者的内存占用必须一致
        EnumWindows(Some(callback), LPARAM(mem::transmute(&mut parm))).unwrap();
    }
    // 如果hwnd被回调函数修改过，这里能看到非零句柄值
    println!("HWND: {:?}, PID: {}", parm.hwnd, parm.pid);
}