Question

我有以下代码：

use bindings::Windows::Win32::DisplayDevices::POINT;
use bindings::Windows::Win32::Gdi::{GetPixel, GetWindowDC, HDC};
use bindings::Windows::Win32::SystemServices::{BOOL, PSTR};
use bindings::Windows::Win32::WindowsAndMessaging::{self, FindWindowA, HWND};
use std::ffi::CString;

fn main() {
    let mut window_name_2 = "Window Title";
    let hwnd;

    unsafe { hwnd = FindWindowA(std::ptr::null_mut(), window_name_2) }
}

它产生错误：

bindings::Windows::Win32::WindowsAndMessaging
pub unsafe fn FindWindowA<'a, T0__, T1__>(lpclassname: T0__, lpwindowname: T1__) -> HWND
where
    T0__: ::windows::IntoParam<'a, super::superSystemServices::PSTR>,
    T1__: ::windows::IntoParam<'a, super::superSystemServices::PSTR>,
the trait bound `*mut _: windows::traits::into_param::IntoParam<'_, PSTR>` is not satisfied
the trait `windows::traits::into_param::IntoParam<'_, PSTR>` is not implemented for `*mut _`rustcE0277
main.rs(1, 1): required by a bound in this
windows.rs(311, 23): required by this bound in `FindWindowA`

我不明白这意味着什么或如何解决它。

Answer 1

version 0.8.0 的更新

windows-rs 包的 0.8.0 版改用 impl Trait，使签名更易于阅读，同时也简化了错误诊断。

鉴于问题中的代码，错误消息现在显示为：

error[E0277]: the trait bound `*mut _: IntoParam<'_, PSTR>` is not satisfied
   --> src\main.rs:11:21
    |
11  |     unsafe { hwnd = FindWindowA(std::ptr::null_mut(), window_name_2) }
    |                     ^^^^^^^^^^^ the trait `IntoParam<'_, PSTR>` is not implemented for `*mut _`
    | 
   ::: C:\...\target\debug\build\findwindow_test-67a9095d9a724f24\out/windows.rs:129:27
    |
129 |             pub unsafe fn FindWindowA<'a>(
    |                           ----------- required by a bound in this
130 |                 lpclassname: impl ::windows::IntoParam<'a, super::SystemServices::PSTR>,
    |                                   ----------------------------------------------------- required by this bound in `FindWindowA`

潜在问题仍然与以前相同（见下文）：IntoParam 特征未针对所涉及的类型组合实现。之前的解决方案（见下文）仍然有效，尽管 0.8.0 版还引入了一个 NULL 常量，因此以下解决方案同样有效：

unsafe { hwnd = FindWindowA(PSTR::NULL, window_name_2) }

GitHub 存储库还引入了一个 FAQ，其中包含有关此特定主题的条目 (How do I read the signatures of generated functions and methods? What's with IntoParam?)

真正的错误信息更有启发性：

error[E0277]: the trait bound `*mut _: IntoParam<'_, PSTR>` is not satisfied
   --> src\main.rs:11:21
    |
11  |     unsafe { hwnd = FindWindowA(std::ptr::null_mut(), window_name_2) }
    |                     ^^^^^^^^^^^ the trait `IntoParam<'_, PSTR>` is not implemented for `*mut _`
    | 
   ::: C:\...\target\debug\build\findwindow_test-805b35ca49628608\out/windows.rs:117:27
    |
117 |             pub unsafe fn FindWindowA<
    |                           ----------- required by a bound in this
118 |                 'a,
119 |                 T0__: ::windows::IntoParam<'a, super::SystemServices::PSTR>,
    |                       ----------------------------------------------------- required by this bound in `FindWindowA`

它告诉你哪个参数不符合要求，即T0__，第一个。无法实现 IntoParam 特性将 *mut _ 转换为 PSTR。 IntoParam trait 的目的是允许在 Rust 类型（如 &str）和 ABI 类型（如 PSTR）之间方便地转换。

为了解决这个问题，你可以构造一个默认的 PSTR 代替，即

unsafe { hwnd = FindWindowA(PSTR::default(), window_name_2) }

PSTR（目前）住在Windows::Win32::SystemServices。

错误消息“此中的边界需要”是什么意思？

1 个答案:

version 0.8.0 的更新