对象的名称可以是任何其他类的名称吗？ [英] Can a name of a object be name of any other class?
问题描述
考虑我有两个A类和B类。是否错误地声明一个名为B的对象是
类型A？
A类{}
B级{}
AB;
为什么会出错？
< vi ******************** @ gmail.com>在消息中写道
news：11 ********************** @ 38g2000cwa.googlegro ups.com ...考虑我有两个A类和B类。声明一个名为B的A类对象是错误的吗？
A类{}
B类{}
AB;
为什么会出错？
令人惊讶的是，这个编译，并且在我的有限测试中确实有效。我会说这是错的，但我不能说为什么。这实际上编译并产生输出10的输出。这是我不希望的。
并不令人惊讶，你不能说
A A;
然而。但如果你能说A B;为什么你不能说AA;？
#include< iostream>
#include< string>
A级{
公开：
int X;
朋友std :: ostream&运营商LT;< （std :: ostream& os，const A& Instance）;
};
std :: ostream&运营商LT;< （std :: ostream& os，const A& Instance）
{
os<< Instance.X;
返回操作系统;
}
B级{};
int main（）
{
AB;
BX = 10;
std :: cout<< B<< std :: endl;
std :: string wait;
std :: cin>>等等;
返回0;
}
它不会给出一个错误，但它不允许实例化类型B的
对象。它不识别calss B的声明。可以
任何人解释？
vi ** ******************@gmail.com 写道：
考虑我有两个A和B类。错误地声明一个名为B的A型对象？
A类{}
B类{}
AB;
为什么会出错？
不是。
[3.3 / 4]
给定一套声明在一个声明区域中，每个声明区域都是
指定相同的不合格名称，
？它们都应引用同一个实体，或全部引用函数和
函数模板;或者
？只有一个声明应声明一个类名或枚举名
不是typedef名称而其他声明都应引用
相同的对象或枚举，或者所有引用功能和功能
模板;在这种情况下，类名或枚举名称是隐藏的。
所以你所做的并不违法，但你隐藏了B类。作为一个编码风格的问题但是，我会远离这些东西。
最好
Kai-Uwe Bux
consider i have two classes A and B. Is it wrong declaring a object of
type A with name B?
class A{}
class B{}
A B;
Why is it wrong?
<vi********************@gmail.com> wrote in message
news:11**********************@38g2000cwa.googlegro ups.com...consider i have two classes A and B. Is it wrong declaring a object of
type A with name B?
class A{}
class B{}
A B;
Why is it wrong?
Suprisingly, this compiles, and in my limited test actually works. I would
say it''s wrong, but I can''t say why. This actually compiles and produces
the output "10" which I would not expect.
Not suprisingly, you can''t say
A A;
however. But if you could say A B; why couldn''t you say A A;?
#include <iostream>
#include <string>
class A {
public:
int X;
friend std::ostream& operator<< (std::ostream& os, const A& Instance );
};
std::ostream& operator<< (std::ostream& os, const A& Instance )
{
os << Instance.X;
return os;
}
class B { };
int main()
{
A B;
B.X = 10;
std::cout << B << std::endl;
std::string wait;
std::cin >> wait;
return 0;
}
It will not give an error but it will not allow to instantiate an
object of type B. It does not identify the declaration of calss B. Can
anyone explain?
vi********************@gmail.com wrote:
consider i have two classes A and B. Is it wrong declaring a object of
type A with name B?
class A{}
class B{}
A B;
Why is it wrong?
It is not.
[3.3/4]
Given a set of declarations in a single declarative region, each of which
specifies the same unqualified name,
? they shall all refer to the same entity, or all refer to functions and
function templates; or
? exactly one declaration shall declare a class name or enumeration name
that is not a typedef name and the other declarations shall all refer to
the same object or enumerator, or all refer to functions and function
templates; in this case the class name or enumeration name is hidden.
So what you are doing is not illegal, but you are hiding class B. As a
matter of coding style, however, I would stay away from such things.
Best
Kai-Uwe Bux
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