无可变持久性 [英] No Variable Permanence
问题描述
Aieeeeaiiieeaiiieii，啊想啊需要一些亲zac
出于某种原因，我的对象变量并没有将它们的值保持在
之外方法范围。例如，给定：
//开始代码
class Parent {
public：
Parent（）{ } $ / $
virtual~Parent（）{}
virtual void setSomething（int thing）{}
virtual int getSomething（）{return 0}
...
};
class孩子：公共父母{
public：
Child（）{...}
Child（int thing）{
...
setSomething（thing）; < br $>
}
~Child（）{...}
void setSomething（int thing）{
something =东西;
}
int getSomething（）{
返回东西;
}
private：
int something;
};
int main（）{
孩子* c;
c =新孩子（12）;
cout<< c.getSomething（）<< endl;
返回0;
}
//结束代码
输出不是12，而是-842150451。我怀疑我正在做虚拟关键字的错误。谁能解释一下呢？
谢谢，
拉里
Aieeeeaiiieeaiiieii, ah think ah need some pro-zac
For some reason, my object variables aren''t keeping their values outside of
the method scope. For instance, given:
//Begin code
class Parent{
public:
Parent(){}
virtual ~Parent(){}
virtual void setSomething(int thing){}
virtual int getSomething(){return 0}
...
};
class Child: public Parent{
public:
Child(){...}
Child(int thing){
...
setSomething(thing);
}
~Child(){...}
void setSomething(int thing){
something=thing;
}
int getSomething(){
return something;
}
private:
int something;
};
int main(){
Child *c;
c = new Child(12);
cout << c.getSomething()<<endl;
return 0;
}
//end code
the output will not be 12, but -842150451. I suspect that I''m doing
something wrong with the virtual keyword. Can anyone explain this?
Thanks,
Larry
推荐答案
Larry Lindsey< gt ***** @ prism.gatech.edu>这样说：
Larry Lindsey <gt*****@prism.gatech.edu> spoke thus:
int main（）{
Child * c;
c = new Child（12）;
cout<< c.getSomething（）<< ENDL;
^^^^^^^^^^^^^^^^ return 0;
}
//结束代码
int main(){
Child *c;
c = new Child(12);
cout << c.getSomething()<<endl; ^^^^^^^^^^^^^^^^ return 0;
}
//end code
你不应该做的吗
c-> getSomething（）
代替？ c是一个指针...
-
Christopher Benson-Manica | Jumonji giri，荣誉。
ataru（at）cyberspace.org |
Shouldn''t you have done
c->getSomething()
instead? c is a pointer...
--
Christopher Benson-Manica | Jumonji giri, for honour.
ataru(at)cyberspace.org |
" Larry Lindsey" < GT ***** @ prism.gatech.edu>在留言中写道
新闻：bk ********** @ news-int.gatech.edu ...
"Larry Lindsey" <gt*****@prism.gatech.edu> wrote in message
news:bk**********@news-int.gatech.edu...
Aieeeeaiiieeaiiieii，啊想啊需要一些pro-zac
出于某种原因，我的对象变量不会将它们的值保持在方法范围的
之外。例如，给定：
//开始代码
class Parent {
public：
Parent（）{}
virtual~Parent（）{}
virtual void setSomething（int thing）{}
virtual int getSomething（）{return 0}
...
};
class Child：public Parent {<公开：
孩子（）{...}
孩子（int thing）{
...
setSomething（thing）;
}
~Child（）{...}
void setSomething（int thing）{
something = thing;
}
int getSomething（）{
返回一些东西;
}
私人：
int something;
};
int main（）{
Child * c;
c =新孩子（12）;
cout<< c.getSomething（）<< endl;
返回0;
}
//结束代码
输出不会是12，而是-842150451。我怀疑我正在做虚拟关键字的错误。任何人都可以解释一下这个吗？
Aieeeeaiiieeaiiieii, ah think ah need some pro-zac
For some reason, my object variables aren''t keeping their values outside of the method scope. For instance, given:
//Begin code
class Parent{
public:
Parent(){}
virtual ~Parent(){}
virtual void setSomething(int thing){}
virtual int getSomething(){return 0}
...
};
class Child: public Parent{
public:
Child(){...}
Child(int thing){
...
setSomething(thing);
}
~Child(){...}
void setSomething(int thing){
something=thing;
}
int getSomething(){
return something;
}
private:
int something;
};
int main(){
Child *c;
c = new Child(12);
cout << c.getSomething()<<endl;
return 0;
}
//end code
the output will not be 12, but -842150451. I suspect that I''m doing
something wrong with the virtual keyword. Can anyone explain this?
拉里，为了您的利益，以及那些试图阅读您的代码的人，请只有
编译后的代码。上面的代码没有编译。除了
....，你不能写c.getSomething。 c是一个指针，所以语法是
c-> getSomething。
Larry, for your benefit, and for those trying to read your code, please only
post code that compiles. The code above doesn''t compile. Aside from the
...., you cannot write c.getSomething. c is a pointer, so the syntax is
c->getSomething.
" Larry Lindsey" ; < GT ***** @ prism.gatech.edu>在留言中写道
新闻：bk ********** @ news-int.gatech.edu ...
"Larry Lindsey" <gt*****@prism.gatech.edu> wrote in message
news:bk**********@news-int.gatech.edu...
Aieeeeaiiieeaiiieii，啊想啊需要一些pro-zac
出于某种原因，我的对象变量不会将它们的值保持在方法范围的
之外。例如，给定：
//开始代码
以下代码不是什么'给出了行为
你描述。它甚至不会编译。
#include< iostream>
使用std :: cout;
使用std :: endl;
class Parent {
public：
Parent（）{}
virtual〜Parent（）{}
virtual void setSomething（int事情）{}
virtual int getSomething（）{return 0}
virtual int getSomething（）const {return 0;}
.. 。
// ...
};
班级孩子：公共家长{
公众：
孩子（ ）{...}
孩子（）{/ * ... * /}
如果你写的是
孩子ch;
你得到一个处于未知状态的物体。
孩子ch2 = ch; / *未定义的行为，评估
未初始化的对象''ch''* /
更好地使用*某种*某种''默认''<当没有指定时，
值，例如：
Child（）：something（0）{}
Child（int thing） {
...
setSomething（thing）;
}
Child（int thing）：something（thing）{}
~Child（）{...}
void setSomething（int thing）{
something = thing;
}
int getSomething（）{
int getSomething（）const {
返回内容;
}
私有：
int something;
};
int main（）{
Child * c;
c = new Child（12）;
cout<< c.getSomething（）<< ENDL;
此行不应编译。 ''点运算符''可以
只能用于struct，class或union类型。 ''c''
不是这些，它是指针。
cout<< c-> getSomething（）<<结束;
最后，就像妈妈总是说的那样，把东西放回原点
你发现它们的方式：
删除c;
返回0;
}
//结束代码
输出不会是12，而是-842150451。
您的代码甚至无法编译。但是我怀疑，当你运行任何版本的这个编译时，你就是
访问成员对象''something''没有
已初始化。
我怀疑我正在做虚拟关键字的错误。
虚拟与此问题无关。
有人可以解释一下吗？
Aieeeeaiiieeaiiieii, ah think ah need some pro-zac
For some reason, my object variables aren''t keeping their values outside of the method scope. For instance, given:
//Begin code
The following code is not what''s giving the behavior
you describe. It won''t even compile.
#include <iostream>
using std::cout;
using std::endl;
class Parent{
public:
Parent(){}
virtual ~Parent(){}
virtual void setSomething(int thing){}
virtual int getSomething(){return 0}
virtual int getSomething() const {return 0;}
...
// ...
};
class Child: public Parent{
public:
Child(){...}
Child() { /* ... */ }
If you write e.g.
Child ch;
you get an object in an unknown state.
Child ch2 = ch; /* undefined behavior, evaluation
of uninitialized object ''ch'' */
Better to use *some* kind of ''default''
value when none is specified, e.g.:
Child() : something(0) {}
Child(int thing){
...
setSomething(thing);
}
Child(int thing) : something(thing) {}
~Child(){...}
void setSomething(int thing){
something=thing;
}
int getSomething(){
int getSomething() const {
return something;
}
private:
int something;
};
int main(){
Child *c;
c = new Child(12);
cout << c.getSomething()<<endl;
This line should not compile. The ''dot operator'' can
only be used with a struct, class, or union type. ''c''
is none of these, it''s a pointer.
cout << c->getSomething() << endl;
And finally, as Mother always said, put things back
the way you found them:
delete c;
return 0;
}
//end code
the output will not be 12, but -842150451.
Your code won''t even compile. But I suspect that when
you ran whatever version of this does compile, you''re
accessing the member object ''something'' which has not
been initialized.
I suspect that I''m doing
something wrong with the virtual keyword.
virtual has nothing to do with the problem.
Can anyone explain this?
见上文。
完整改编你的代码，给出预期结果
：
#include< iostream>
使用std :: cout;
使用std :: endl;
class Parent {
public：
Parent（）{}
virtual~Parent（）{}
virtual void setSomething（int thing）{ } $ / $
virtual int getSomething（）const {return 0;}
};
class Child：public Parent {
public：
Child（）{}
Child（int thing）：something（thing）{}
~ Child（）{}
void setSomething（int thing）{
something = thing;
}
int getSomething（）const {
返回一些东西;
}
私人：
int something;
};
int main（）{
Child * c;
c =新孩子（12）;
cout<< c-> getSomething（）<< endl;
返回0;
}
输出：
12
HTH，
-Mike
See above.
A complete adaptation of your code that gives
the expected result:
#include <iostream>
using std::cout;
using std::endl;
class Parent {
public:
Parent() {}
virtual ~Parent() {}
virtual void setSomething(int thing) {}
virtual int getSomething() const {return 0;}
};
class Child: public Parent{
public:
Child() {}
Child(int thing) : something(thing) {}
~Child() {}
void setSomething(int thing){
something=thing;
}
int getSomething() const {
return something;
}
private:
int something;
};
int main(){
Child *c;
c = new Child(12);
cout << c->getSomething()<<endl;
return 0;
}
Output:
12
HTH,
-Mike
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