VBScript 函数中的变量范围 [英] Variable scope in VBScript functions

问题描述

我有一个关于 VBScript 中变量作用域的问题.我知道有以下关键字(来自 autoitscript.com):

I have a question about variable scope in VBScript. I know there's the following keywords (from autoitscript.com):

1. Dim = 局部作用域，如果变量名在全局不存在(在这种情况下它重用全局变量！)
2. Global = 强制在全局范围内创建变量
3. Local = 强制在 Local/Function 范围内创建变量

假设我有以下 .vbs 文件:

Imagine that I have the following .vbs file:

Dim strPath

strPath = "C:\folder"

DisplayPath strPath

Sub DisplayPath(strPath) 'Does this strPath get it's own local scope?
  MsgBox strPath
End Sub

在函数:DisplayPath(strPath)中，strPath是局部变量吗?或者函数/子函数是否可以访问在脚本主要部分顶部定义的 strPath 作为全局变量?

In the function: DisplayPath(strPath), is strPath a local variable? Or do functions/subs have access to the strPath defined at the top of the main section of the script as a global variable?

此外，明确使用 Dim 与仅在我使用变量时定义变量有什么意义，这在脚本语言中是可能的?

Also, what's the point of explicitly using Dim versus just defining variables as I use them, which is possible in scripting languages?

推荐答案

DisplayPath 过程中的 strPath 将是一个新变量，但不是出于您预期的原因，您的代码存在细微的问题，会使问题变得模糊.

The strPath in the DisplayPath procedure will be a new variable but not for the reasons you expect, there is subtle problem with your code that will cloud the issue.

当调用 Sub 过程时，VBScript 语法不包括括号.例如:-

When calling Sub procedure the VBScript syntax does not include parentheses. For example:-

Sub MyProc(Param1, Param2)
  '' # Do stuff
End Sub

MyProc("Hello", "World")

以上会导致语法错误.它应该被称为:-

the above would result in a syntax error. It should be called:-

MyProc "Hello", "World"

现在当只有一个参数时不会发生语法错误.这是因为括号的另一种用法是作为表达式的一部分，例如'(a + b) * c'.在以下情况下:-

Now when there is only one parameter a syntax error does not occur. This is because another use of parentheses is as part of an expression e.g. '(a + b) * c'. In the case of:-

DisplayPath(strPath)

VBScript 解析表达式"(strPath) 并将结果 传递给DisplayPath.产生新存储的这个结果保存了结果表达式.

VBScript resolves the "expression" (strPath) and pass the result to DisplayPath. Its this result that gives rise to new storage hold the result the expression.

你打电话了吗

DisplayPath strPath

没有新建.

但是这又如何:-

Sub DisplayPath(something)
  MsgBox something
End Sub

仍然没有分配新的存储空间.something 将指向与 strPath 相同的内存.

There is still no new storage allocated. something will point at the same memory that strPath does.

编辑

以下代码有效:-

Dim strPath

strPath = "c:\folder"

Display


Sub Display()
  MsgBox strPath
End Sub

在过程之外声明 strPath 使其具有全局作用域.

The declaration of strPath outside of a procedure causes it to have global scope.

至于使用显式Dim 如果上面的赋值行看起来像这样会发生什么?

As to the point of using explicit Dim what would happen if the assignment line above looked like this?

 strPath = "c:\folder"

一个名为 strPath 的新变量将出现，而 strPath 将保持为空.您应该总是以以下行开始您的 VBScript 文件:-

A new variable called strPath would come into existence and strPath would remain empty. You should always begin your VBScript files with the line:-

Option Explicit

这将强制您显式Dim要使用的所有变量，并为您节省数小时的调试时间.

This will force you to explicitly Dim all variables to be used and will save you hours of debugging time.

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