如何传递const引用？ [英] how to pass by const reference?
问题描述
为什么VB.NET V2强迫我为我的set函数传递值？当我尝试将
更改为const byref时，它会给我一个语法错误。当对一个
常量字符串对象的引用会很好的时候，通过值传递字符串似乎非常有效（我们要做的就是复制它）。在
我的情况下，set函数的byval会导致多余的副本吗？
谢谢，
齐格弗里德
班级人员
dim m_name as string
public sub new（n as string）
m_name = n
end sub
公共财产名称（）为字符串
获取
返回m_name
结束获取
set（const byref value as string）
m_name = value
end set
end property
公共重载覆盖函数ToString（）as string
return m_name
end function
protected overloads覆盖sub Finalize（）
outp.WriteLine（"〜"& name）
MyBase.Finalize（）
end sub
结束类
Why does VB.NET V2 force me to pass by value for my set function? When I try
to change it to const byref it gives me a syntax error. It seems very
inefficient to be passing strings around by value when a reference to a
constant string object will do fine (all we are going to do is copy it). In
my case, would the byval for the set function cause a superfluous copy?
Thanks,
Siegfried
class person
dim m_name as string
public sub new (n as string)
m_name = n
end sub
public property name () as string
Get
return m_name
end get
set ( const byref value as string)
m_name = value
end set
end Property
public overloads overrides function ToString() as string
return m_name
end function
protected overloads overrides sub Finalize()
outp.WriteLine("~" & name )
MyBase.Finalize()
end sub
End Class
推荐答案
" Siegfried Heintze" < si ******* @ heintze.com写信息
新闻：OH **************** @ TK2MSFTNGP06.phx.gbl。 ..
"Siegfried Heintze" <si*******@heintze.comwrote in message
news:OH****************@TK2MSFTNGP06.phx.gbl...
为什么VB.NET V2强迫我为我的set函数传递值？当我将
尝试将其更改为const byref时，它会给我一个语法错误。当对一个
常量字符串对象的引用会很好的时候，通过值传递字符串似乎非常有效（我们要做的就是复制它）。
在我的情况下，set函数的byval是否会导致多余的副本？
Why does VB.NET V2 force me to pass by value for my set function? When I
try to change it to const byref it gives me a syntax error. It seems very
inefficient to be passing strings around by value when a reference to a
constant string object will do fine (all we are going to do is copy it).
In my case, would the byval for the set function cause a superfluous copy?
它不会创建字符串的第二个副本，只是指向它的指针。所以
你有2个指针指向1个字符串。如果你从
1指针更改字符串，它会创建一个副本然后我相信。
Michael
It doesn''t create a second copy of the string, just the pointer to it. So
you have 2 pointers pointing to the 1 string. If you change the string from
1 pointer it will create a copy then I believe.
Michael
为什么VB.NET V2强制我为我的set函数传递值？
Why does VB.NET V2 force me to pass by value for my set function?
set（const byref value as string）
set ( const byref value as string)
我从未听说过这里使用的const关键字。
尝试跳过它。
-
Rory
I have never heard of the const keyword being used here.
Try skipping it.
--
Rory
" Michael C" < mi ** @ nospam.comwrote in message
news：u2 ************* @ TK2MSFTNGP04.phx.gbl ...
"Michael C" <mi**@nospam.comwrote in message
news:u2*************@TK2MSFTNGP04.phx.gbl...
" Siegfried Heintze" < si ******* @ heintze.com写信息
新闻：OH **************** @ TK2MSFTNGP06.phx.gbl。 ..
"Siegfried Heintze" <si*******@heintze.comwrote in message
news:OH****************@TK2MSFTNGP06.phx.gbl...
>为什么VB.NET V2强迫我为我的set函数传递值？当我尝试将其更改为const byref时，它会给我一个语法错误。当对
常量字符串对象的引用会很好的时候，通过值传递字符串似乎非常低效（我们要做的就是复制它）。
就我而言， set函数的byval会导致多余的复制吗？
>Why does VB.NET V2 force me to pass by value for my set function? When I
try to change it to const byref it gives me a syntax error. It seems very
inefficient to be passing strings around by value when a reference to a
constant string object will do fine (all we are going to do is copy it).
In my case, would the byval for the set function cause a superfluous
copy?
它不会创建字符串的第二个副本，只是指向它的指针。所以
你有2个指针指向1个字符串。如果你从1指针改变字符串
它会创建一个副本然后我相信。
It doesn''t create a second copy of the string, just the pointer to it. So
you have 2 pointers pointing to the 1 string. If you change the string
from 1 pointer it will create a copy then I believe.
这是正确的。默认情况下，VB .NET中的所有参数都传递ByVal和
传递参数ByVal意味着你得到一个副本 - 但不一定是数据的b / b
副本。如果你传递一个引用类型（字符串是）ByVal，
你得到一个指向引用类型的指针的副本，因此有两种方法可以获得
访问一个内存地址。如果你传递一个值类型（比如一个整数）
ByValue，那么你得到一个存储在堆栈上的实际数据的副本。
如果你是传递引用类型（String）ByRef，然后你会得到一个指向原始指针的
指针，它指向内存。指向
指针的指针不如第一个指针的副本效率高。
That is correct. By default all arguments in VB .NET are passes ByVal and
passing an argument ByVal means you get a copy - - but not necessarially a
copy of the data. If you pass a reference type (which a String is) ByVal,
you get a copy of the pointer to the reference type, thus having two ways to
access the one memory address. If you pass a value type (like an Integer)
ByValue, then you get a copy of the actual data stored on the stack.
If you were to pass a reference type (String) ByRef, then you''d get a
pointer to the original pointer, which points to the memory. A pointer to a
pointer is not as effiicient as a copy of the first pointer.
>
Michael
>
Michael
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