演员无效??? [英] Cast to void???
问题描述
在Loki（smartptr.h）中，我注意到以下表达式由
本身发生：
（void）val;
使某些内容无效的目的是什么，特别是在这样的单独表达式中，而不是作为更大的一部分的一部分？
我很惊讶这是可能的，因为无法声明类型为void的变量
。我很想学习目的...
这是我在上面看到的背景：
static void OnDereference（P val）
{assert（val）; （空隙）VAL; }
BTW，我在Loki的VC ++端口看到这个。我不知道它是否在
原版Loki中......
谢谢，
Dave
In Loki (smartptr.h), I''ve noticed the following expression occurring by
itself:
(void)val;
What is the purpose in casting something to void, especially in a
stand-alone expression such as this and not as part of something larger?
I''m surprised this is possible as it is not possible to declare a variable
of type void. And I''m intrigued to learn the purpose...
Here''s the context I see this in:
static void OnDereference(P val)
{ assert(val); (void)val; }
BTW, I see this in the VC++ port of Loki. I don''t know if it''s in the
original Loki or not...
Thanks,
Dave
推荐答案
Dave Theese写道：
Dave Theese wrote:
在Loki（smartptr.h）中，我注意到以下表达式单独发生：
（void）val;
使某些内容无效的目的是什么，特别是在
独立表达式中比如这个而不是作为更大的东西的一部分？我很惊讶这是可能的，因为不可能声明一个void类型的变量。我很想学习
目的......
In Loki (smartptr.h), I''ve noticed the following expression occurring
by itself:
(void)val;
What is the purpose in casting something to void, especially in a
stand-alone expression such as this and not as part of something
larger? I''m surprised this is possible as it is not possible to
declare a variable of type void. And I''m intrigued to learn the
purpose...
[SNIP]
我第一次看到这个和我能想象的唯一原因就是避免编译
时间警告未使用的变量。
-
WW aka Attila
[SNIP]
First time I see this and the only reason I can imagine is to avoid compile
time warnings for unused variables.
--
WW aka Attila
> Dave Theese写道：
> Dave Theese wrote:
在Loki（smartptr.h）中，我注意到以下表达单独出现
（void）val;
什么是使某些东西无效的目的，特别是在这样的独立表达中，而不是作为某种东西的一部分
更大？我很惊讶这是可能的，因为不可能声明一个void类型的变量。我很想学习
目的... [SNIP]
我第一次看到这个，我能想象的唯一原因就是避免
In Loki (smartptr.h), I''ve noticed the following expression occurring
by itself:
(void)val;
What is the purpose in casting something to void, especially in a
stand-alone expression such as this and not as part of something
larger? I''m surprised this is possible as it is not possible to
declare a variable of type void. And I''m intrigued to learn the
purpose... [SNIP]
First time I see this and the only reason I can imagine is to avoid
未使用变量的编译时警告。
compile time warnings for unused variables.
不需要这个。可以简单地省略未使用的参数名称。
No need for this however. An unused parameter name can simply be omitted.
John Almer写道：
[SNIP]
John Almer wrote:
[SNIP]
我第一次看到这个，我能想象的唯一原因就是避免对未使用的变量进行编译时警告。
First time I see this and the only reason I can imagine is to avoid
compile time warnings for unused variables.
不需要但是这个。可以简单地省略未使用的参数名称。
No need for this however. An unused parameter name can simply be
omitted.
是。但是我谈到了一个参数吗？
这是模板元编程魔法的深层内容。我很容易想象它
是在某些情况下不用于函数的某种变量。
-
WW又名阿提拉
Yes. But did I talk about a paramneter?
It is deep inside template metaprogramming magic. I can easily imagine it
was some sort of variable not used in a function in certain cases.
--
WW aka Attila
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