NOT的怪异行为

问题描述

我正在遇到一些布尔变量的怪异行为；以下代码同时显示"Hello"和"There"，表示result& NOT result均评估为True

I'm experiencing some weird behaviour of boolean variables; the following code prints both "Hello" and "There", meaning result & NOT result both evaluate to True

Dim result As Boolean
result = PostMessage(Application.hWnd, 275, 0, 0)
Debug.Print "Post message: "; result
If result Then Debug.Print "Hello"
If Not result Then Debug.Print "There"

输出

Post message: True
Hello
There

---

根据文档， PostMessage 的声明如下:

---

According to the docs, PostMessage is declared like this:

BOOL PostMessageA(
  HWND   hWnd,
  UINT   Msg,
  WPARAM wParam,
  LPARAM lParam
);

带有评论:

这是我在VBA中的使用方式:

Here's how I have it in VBA:

Public Declare Function PostMessage Lib "user32" Alias "PostMessageA" ( _
                        ByVal hWnd As LongPtr, _
                        ByVal msg As Long, _
                        ByVal wParam As LongPtr, _
                        ByVal lParam As LongPtr) As Boolean

那是什么导致怪异的行为呢?我该如何解决?

So what's causing the weird behaviour? How do I get around it?

推荐答案

尽管通常 VBA Boolean可以容纳True(-1)或False(0) ，可能会有些诡异地在此类型中插入另一个值.

Although normally a VBA Boolean holds either True (-1) or False (0), it is possible to insert another value into this type with some trickery.

这就是这里发生的情况:您错误指定的API调用返回的整数类型的值既不是-1也不是0.

This is what is happening here: your mis-specified API call is returning an integral type with a value that's neither -1 nor 0.

由于NOT(a)是0，并且仅当a是-1时，如果Boolean中的有效载荷不是-1或-1，则将同时打印Hello和There. 0.

Since NOT(a) is 0 if and only if a is -1, both Hello and There will be printed if the payload in the Boolean is anything other than -1 or 0.

这篇关于NOT的怪异行为的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！