开关，外壳，以及它有时如何让你跌倒 [英] switch, case, and how it sometimes lets you fallthrough

问题描述

我很困惑如何在开关中限制穿透。例如

以下作品：


string switch_test =" a" ;;

开关（switch_test）

{

case" a"：

case" b"：

case" c"：

doSomething（a）;

休息;

}


但以下不起作用：

string switch_test =" a" ;;

switch（switch_test）

{

case" a"：

if（< some test>）

break;

case" b"：

case" c"：

doSomething（a）;

}

为什么会这样？

I''m confused as to how fallthrough is limited in switch. For example
the following works:

string switch_test = "a";
switch (switch_test)
{
case "a":
case "b":
case "c":
doSomething(a);
break;
}

but the following does not work:
string switch_test = "a";
switch (switch_test)
{
case "a":
if (<some test>)
break;
case "b":
case "c":
doSomething(a);
}
why is that?

推荐答案

案例必须为空，或通过''jump''语句退出（中断，继续，

返回等）。


如果你只是在dosomething（a）行之后包含一个跳转（通常是'break''）

，那么第二个例子也会有用，并确保跳转到达在

第一种情况下（目前，只有在if测试为真的情况下才会达到）。

-

David Anton
www.tangiblesoftwaresolutions.com

即时C＃：VB .NET到C＃转换器

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" Benny Raymond"写道：

A case must either be empty, or exit via a ''jump'' statement (break, continue,
return, etc.).

The second example will work if you just include a jump (usually ''break'')
after the dosomething(a) line and also ensure that a jump is reached in the
first case (currently, it''s only reached if the if test is true).
--
David Anton
www.tangiblesoftwaresolutions.com
Instant C#: VB.NET to C# Converter
Instant VB: C# to VB.NET Converter
Instant C++: C# to C++ Converter
Instant J#: VB.NET to J# Converter

"Benny Raymond" wrote:

我很困惑如何在开关中限制穿透。例如
以下工作：

string switch_test =" a" ;;
switch（switch_test）
{
case" a"：
case" b"：
case" c"：
doSomething（a）;
break;
}

但以下不起作用：
string switch_test =" a" ;;
switch（switch_test）
{
case" a"：
if（< some test> ）
休息;
案例" b"：
案例" c"：
doSomething（a）;
}

为什么是吗？

I''m confused as to how fallthrough is limited in switch. For example
the following works:

string switch_test = "a";
switch (switch_test)
{
case "a":
case "b":
case "c":
doSomething(a);
break;
}

but the following does not work:
string switch_test = "a";
switch (switch_test)
{
case "a":
if (<some test>)
break;
case "b":
case "c":
doSomething(a);
}
why is that?

这不是解决这个问题，但我想指出你的陈述

也应该有一个''默认''开关，以尽量减少未处理的错误。


像这样：

string switch_test =" a";


开关（switch_test）

{

case" a"：

{

if（this）

休息;

其他

do_somthing_nice（switch_test）;

休息;

}

case" b"：

case" c："

{

do_something_naughty（switch_test）;

休息;

}

默认值：

{

whine_about（switch_test）;

休息;

}

}


" Benny Raymond"写道：

This isn''t a fix for this, but I wanted to point out that your statement
should also have a ''default'' switch to minimize unhandled errors.

like this:

string switch_test = "a";

switch(switch_test)
{
case "a":
{
if (this)
break;
else
do_somthing_nice(switch_test);
break;
}
case "b":
case "c:"
{
do_something_naughty(switch_test);
break;
}
default:
{
whine_about(switch_test);
break;
}
}

"Benny Raymond" wrote:

我很困惑如何在开关中限制穿透。例如
以下工作：

string switch_test =" a" ;;
switch（switch_test）
{
case" a"：
case" b"：
case" c"：
doSomething（a）;
break;
}

但以下不起作用：
string switch_test =" a" ;;
switch（switch_test）
{
case" a"：
if（< some test> ）
休息;
案例" b"：
案例" c"：
doSomething（a）;
}

为什么是吗？

I''m confused as to how fallthrough is limited in switch. For example
the following works:

string switch_test = "a";
switch (switch_test)
{
case "a":
case "b":
case "c":
doSomething(a);
break;
}

but the following does not work:
string switch_test = "a";
switch (switch_test)
{
case "a":
if (<some test>)
break;
case "b":
case "c":
doSomething(a);
}
why is that?

我知道......我只是想知道如何只打破a如果

什么 - 否则会掉线。


Kevin Kitching写道：

I know... I just was mainly wondering about how to only break on "a" if
something - otherwise fallthough.

Kevin Kitching wrote:

这不是解决这个问题，但我想要指出你的陈述
也应该有一个''默认''开关，以尽量减少未处理的错误。

这样：

string switch_test =" a" ;;

开关（switch_test）
{
案例a：
{
if（this）
break;
其他
do_somthing_nice（switch_test）;
休息;
}
案例" b"：
案例" c："
{
do_something_naughty（switch_test）;
休息;
}
默认：
{
whine_about（switch_test）;
休息;
}
}

Benny Raymond写道：

This isn''t a fix for this, but I wanted to point out that your statement
should also have a ''default'' switch to minimize unhandled errors.

like this:

string switch_test = "a";

switch(switch_test)
{
case "a":
{
if (this)
break;
else
do_somthing_nice(switch_test);
break;
}
case "b":
case "c:"
{
do_something_naughty(switch_test);
break;
}
default:
{
whine_about(switch_test);
break;
}
}

"Benny Raymond" wrote:

我很困惑如何在开关中限制穿透。例如
以下工作：

string switch_test =" a" ;;
switch（switch_test）
{
case" a"：
case" b"：
case" c"：
doSomething（a）;
break;
}

但以下不起作用：
string switch_test =" a" ;;
switch（switch_test）
{
case" a"：
if（< some test> ）
休息;
案例" b"：
案例" c"：
doSomething（a）;
}

为什么是吗？

I''m confused as to how fallthrough is limited in switch. For example
the following works:

string switch_test = "a";
switch (switch_test)
{
case "a":
case "b":
case "c":
doSomething(a);
break;
}

but the following does not work:
string switch_test = "a";
switch (switch_test)
{
case "a":
if (<some test>)
break;
case "b":
case "c":
doSomething(a);
}
why is that?

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