问：继承设计问题 [英] Q: Inheritance design issue
问题描述
假设我有一个基类和一个派生类，如下所示：
class base
{
public：
void somefunc（）;
};
派生类：私人基地
{
public：
void someotherfunc（）;
};
我打算阻止''derived''的用户访问
''base''的成员。问题是，没有什么能阻止用户将'b $ b''派生''类下放到''base''类，然后访问该成员。除了简单记录之外，还有一个
的解决方案吗？
谢谢！
-
jb
（如果你想通过电子邮件回复，用x替换y）
< blockquote>
" Jakob Bieling" <是ne ***** @ gmy.net>在消息新闻中写道：bm ************* @ news.t-online.com ...
我的打算是阻止''derived''的用户访问
''base''的成员。问题是，没有什么能阻止用户将派生类转储到基础类，然后访问该成员。除了简单地记录它之外，还有解决方案吗？
向下转换为base的唯一方法（安全地）是使用C风格的转换。那个'C $风格的演员将扮演的C ++演员不会这样做。为了通过
C ++强制转换（甚至隐式转换），基类需要是可访问的（即，
不是私有的）。 reinterpret_cast是危险的（不能保证转换后的
指针是正确的，并且在多重继承的情况下，它几乎可以肯定是某些错误的。基础）。
Jakob Bieling写道：
假设我有一个基地class和派生类如下：
class base
{
public：
void somefunc（）;
};
类派生：私人基地
公开：
void someotherfunc（）;
};
我打算阻止用户' '衍生''访问''base''的成员。
为什么？继承的整个想法是''派生''可以像
a''base''一样使用并共享其界面。如果你需要另一个界面，
考虑派生一个基础成员。
问题是没有什么能阻止用户下传
''派生''类到''base''类然后访问该成员。是否有解决方案，除了简单记录它？
再次，派生一个基地的成员。
Rolf Magnus写道：
Jakob Bieling写道：
<假设我有一个基类和一个派生类，如下所示：
class base
{
public：
void somefunc（）;
派生类：私人基地
{
公开：
void someotherfunc（）;
};
我的打算防止''derived''的用户访问''base''的成员。
为什么？继承的整个想法是''派生''可以像''base'一样使用
并共享它的界面。如果你需要另一个界面，
考虑派生一个基础成员。
问题是没有什么能阻止用户下传
''派生''类到''base''类然后访问该成员。是否有解决方案，除了简单记录它？
再次，使派生成为基础成员。
Grmbl。在发送
之前，我已经习惯了不再阅读我的帖子，这不是一个好主意。当然我的意思是让基地成员
派生。
Hi,
Suppose I have a base class and a derived class as follows:
class base
{
public:
void somefunc ();
};
class derived : private base
{
public:
void someotherfunc ();
};
My intend is to prevent the user of ''derived'' to access the members of
''base''. The problem is that nothing prevents the user to down-cast the
''derived'' class to the ''base'' class and then access that member. Is there a
solution to this, other than simply documenting it?
thanks!
--
jb
(replace y with x if you want to reply by e-mail)
"Jakob Bieling" <ne*****@gmy.net> wrote in message news:bm*************@news.t-online.com...
My intend is to prevent the user of ''derived'' to access the members of
''base''. The problem is that nothing prevents the user to down-cast the
''derived'' class to the ''base'' class and then access that member. Is there a
solution to this, other than simply documenting it?
The only way (safely) to down convert derived to base is to use a C-style cast. That''s
the one cast the C-style cast will do that the C++ casts won''t. In order to cast via a
C++ cast (or even implicitly convert) the base class would need to be accessible (i.e.,
not private). A reinterpret_cast is dangerous (there''s no guarantee that the converted
pointer would be correct, and in the case of multiple inheritance it almost assuredly is
wrong for some of the bases).
Jakob Bieling wrote:
Hi,
Suppose I have a base class and a derived class as follows:
class base
{
public:
void somefunc ();
};
class derived : private base
{
public:
void someotherfunc ();
};
My intend is to prevent the user of ''derived'' to access the
members of ''base''.
Why? The whole idea of inheritance is that a ''derived'' can be used like
a ''base'' and shares its interface. If you need another interface,
consider making derived a member of base.
The problem is that nothing prevents the user to down-cast the
''derived'' class to the ''base'' class and then access that member. Is
there a solution to this, other than simply documenting it?
Again, make derived a member of base.
Rolf Magnus wrote:
Jakob Bieling wrote:Hi,
Suppose I have a base class and a derived class as follows:
class base
{
public:
void somefunc ();
};
class derived : private base
{
public:
void someotherfunc ();
};
My intend is to prevent the user of ''derived'' to access the
members of ''base''.
Why? The whole idea of inheritance is that a ''derived'' can be used
like a ''base'' and shares its interface. If you need another interface,
consider making derived a member of base.The problem is that nothing prevents the user to down-cast the
''derived'' class to the ''base'' class and then access that member. Is
there a solution to this, other than simply documenting it?
Again, make derived a member of base.
Grmbl. I just got used to not reading my postings anymore before sending
them, which is not a good idea. Of course I mean making base a member
of derived.
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