未初始化的变量 [英] Uninitialized variables

问题描述

这是预期的行为吗？


Winform按钮和列表框：


Dim i As Integer

对于i = 0到50

Dim s As String

如果i = 1那么

s ="只有一次？"

结束如果

Me.ListBox1.Items.Add（" Test" s）

Next


如果我运行此代码，我发现s的值仍然是

只有一次？通过i = 1之后的所有迭代，尽管

它没有被声明为静态。


这肯定是（可能）在C中发生的一个

未初始化的变量，但是我虽然VB是超级安全的并且

会自动将变量初始化为合理的默认值？


如果没有当然VB编译器应该做C＃

编译器做的事情并检查未初始化的变量？


Tim

Is this expected behavior?

Winform with button and listbox:

Dim i As Integer
For i = 0 To 50
Dim s As String
If i = 1 Then
s = "Only once?"
End If
Me.ListBox1.Items.Add("Test " & s)
Next

If I run this code I find that the value of s remains at
"Only once?" through all the iterations after i=1, although
it is not declared as static.

This is certainly what (might) happen in C with an
uninitialized variable, but I though VB was super-safe and
would automatically initialize variables to a sensible default?

If not, surely the VB compiler should do what the C#
compiler does and check for uninitialized variables?

Tim

推荐答案

您使用的是什么版本的.NET？


-

HTH，
- Tom Spink，überGeek


请回复新闻组，

所以所有人都可以受益


也许它是一款名为''惩罚用户''的游戏，

Tim Anderson" < TI ***** @ hotmail.com>在消息中写道

news：e8 ************* @tk2msftngp13.phx.gbl ...

What version of .NET are you using?

--
HTH,
-- Tom Spink, über Geek

Please respond to the newsgroup,
so all can benefit

"Maybe it''s a game called ''Punish the User''"
"Tim Anderson" <ti*****@hotmail.com> wrote in message
news:e8*************@tk2msftngp13.phx.gbl...

这是预期的行为吗？带按钮和列表框的Winform：

Dim i As Integer
对于i = 0到50
Dim s As String
如果i = 1然后
s =只有一次？
结束如果
Me.ListBox1.Items.Add（" Test" s）
Next

如果我运行此代码，我发现s的值仍然是
只有一次？通过i = 1之后的所有迭代，虽然它没有被声明为静态。

这肯定是（可能）在C中发生的
未初始化变量，但我虽然VB是超级安全的，并且会自动将变量初始化为合理的默认值？

如果没有，那么VB编译器肯定应该执行C＃
编译器所做的事情并检查未初始化的变量？

Tim

Is this expected behavior?

Winform with button and listbox:

Dim i As Integer
For i = 0 To 50
Dim s As String
If i = 1 Then
s = "Only once?"
End If
Me.ListBox1.Items.Add("Test " & s)
Next

If I run this code I find that the value of s remains at
"Only once?" through all the iterations after i=1, although
it is not declared as static.

This is certainly what (might) happen in C with an
uninitialized variable, but I though VB was super-safe and
would automatically initialize variables to a sensible default?

If not, surely the VB compiler should do what the C#
compiler does and check for uninitialized variables?

Tim

你好，


"蒂姆安德森 < TI ***** @ hotmail.com> schrieb：

Hello,

"Tim Anderson" <ti*****@hotmail.com> schrieb:

这是预期的行为吗？

Winform with button and listbox：

Dim i As Integer
for i = 0 To 50
Dim s As String
如果i = 1那么
s =只有一次？
结束如果
Me.ListBox1.Items.Add（" ;测试& s）


如果我运行此代码，我发现s的值仍然是
只有一次？通过i = 1后的所有迭代，虽然它没有被声明为静态。


那是恕我直言的预期行为：


\\\

Dim i As整数

对于i = 1到2

Dim s As String

如果i = 1那么

s =" ;只有一次？

结束如果

MsgBox

下一页i

///


将显示仅一次？两次。请注意，在循环的每次迭代中，s将被_not_销毁并重新分配。

这肯定是（可能）在C中发生的
未初始化的变量，但我虽然VB是超级安全的，并且
会自动将变量初始化为合理的默认值？

Is this expected behavior?

Winform with button and listbox:

Dim i As Integer
For i = 0 To 50
Dim s As String
If i = 1 Then
s = "Only once?"
End If
Me.ListBox1.Items.Add("Test " & s)
Next

If I run this code I find that the value of s remains at
"Only once?" through all the iterations after i=1, although
it is not declared as static.
That''s IMHO the expected behavior:

\\\
Dim i As Integer
For i = 1 To 2
Dim s As String
If i = 1 Then
s = "Only once?"
End If
MsgBox(s)
Next i
///

Will show "Only once?" two times. Notice that s will _not_ be destroyed and
re-allocated in every iteration of the loop.
This is certainly what (might) happen in C with an
uninitialized variable, but I though VB was super-safe and
would automatically initialize variables to a sensible default?

变量将在迭代中保持不变环。让我们看看下面的代码：


\\\

Dim i As Integer

对于i = 1到2

Dim s As String =""

如果i = 1那么

s ="只有一次？

结束如果

MsgBox

下一页我

///


上面的代码与此相同：


\\\

Dim i As Integer

For i = 1 to 2

Dim s As String

s =""

如果i = 1那么

s ="只有一次？

结束如果

MsgBox

接下来我们

///


在这两种情况下，s只会被分配一次并且不会被销毁

（好的，为字符串变量分配一个新值会创建一个新字符串，但是

这不是我想说的）。


问候，

Herfried K. Wagner

-

MVP·VB Classic，VB .N ET
http://www.mvps.org/dotnet

Tim，


您的字符串是使用块范围定义的，其中块是For / Next

循环。你永远不会离开它，所以它不会被重新定义。


拉里伍兹


Tim Anderson < TI ***** @ hotmail.com>在消息中写道

news：e8 ************* @tk2msftngp13.phx.gbl ...

Tim,

Your string is defined with block scope, where the block is the For/Next
loop. You never leave it, so it doesn''t get redefined.

Larry Woods

"Tim Anderson" <ti*****@hotmail.com> wrote in message
news:e8*************@tk2msftngp13.phx.gbl...

这是预期的行为吗？带按钮和列表框的Winform：

Dim i As Integer
对于i = 0到50
Dim s As String
如果i = 1然后
s =只有一次？
结束如果
Me.ListBox1.Items.Add（" Test" s）
Next

如果我运行此代码，我发现s的值仍然是
只有一次？通过i = 1之后的所有迭代，虽然它没有被声明为静态。

这肯定是（可能）在C中发生的
未初始化变量，但我虽然VB是超级安全的，并且会自动将变量初始化为合理的默认值？

如果没有，那么VB编译器肯定应该执行C＃
编译器所做的事情并检查未初始化的变量？

Tim

Is this expected behavior?

Winform with button and listbox:

Dim i As Integer
For i = 0 To 50
Dim s As String
If i = 1 Then
s = "Only once?"
End If
Me.ListBox1.Items.Add("Test " & s)
Next

If I run this code I find that the value of s remains at
"Only once?" through all the iterations after i=1, although
it is not declared as static.

This is certainly what (might) happen in C with an
uninitialized variable, but I though VB was super-safe and
would automatically initialize variables to a sensible default?

If not, surely the VB compiler should do what the C#
compiler does and check for uninitialized variables?

Tim

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