blocks|key|437551|text|count似乎与您的vector大小相同。在推回最后一个元素之后，您不会递增count，所以打印的是一个较旧的元素。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|437552|你为什么不试试：|437553|cout<<v[v.size()-1]->getName<<endl;
cout<<v[v.size()-1]->getNumber<<endl;|code-block|syntax|javascript|437554|此外，您应该开始在构造函数中使用初始化列表：|437555|Bed::Bed(int+number,+string+name,+string+frm,+string+fclr,+string+mtres)+:
++Item(name,number),
++frame(frm),
++frameColour(fclr),
++mattress(mtres)
{
}|437556|entityMap^0|0|5|A|6|12|5|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|10|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|11|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|12|8|@]|D|@]|E|$K|L]]|$1|Q|3|-4|5|6|7|13|8|@]|D|@]|E|$]]]|R|$]]

<code>count</code> appears to be the size of your <code>vector</code>. After you push back the last element, you're not incrementing <code>count</code>, so you're printing an older element. 

Why don't you try:

<pre><code>cout&lt;&lt;v[v.size()-1]-&gt;getName&lt;&lt;endl;
cout&lt;&lt;v[v.size()-1]-&gt;getNumber&lt;&lt;endl;
</code></pre>

Also, you should start using initialization lists in your constructors:

<pre><code>Bed::Bed(int number, string name, string frm, string fclr, string mtres) :
 Item(name,number),
 frame(frm),
 frameColour(fclr),
 mattress(mtres)
{
}
</code></pre>

blocks|key|1270692|text|您尚未从派生类调用基类的构造函数...它应该是第一行……更新代码，我相信它会开始工作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1270693|编辑|offset|length|style|BOLD|1270694|如果不是这样，你可能还应该检查一下你处理计数变量的方式...正如其他人指出的那样..|1270695|entityMap^0|0|0|2|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@$D|N|E|O|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

You have not called the base class's constructor from the derived class... Where as it should be the first line... update the code, I am sure it will start working..

EDIT

If it doesn't than you should probably also check the way you are handling count variable... as pointed out by others..

blocks|key|1272170|text|这看起来不正确(我甚至不确定它是如何编译的)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1272171|cout<<v[count]->getName<<endl;
cout<<v[count]->getNumber<<endl;+|code-block|syntax|javascript|1272172|因为getName和getNumber都是方法。更改为：|offset|length|style|CODE|1272173|cout<<v[count]->getName()<<endl;
cout<<v[count]->getNumber()<<endl;|1272174|此外，count的初始化没有发布:请确保它是零。|1272175|entityMap^0|0|0|2|7|A|9|0|0|3|5|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@$I|V|J|W|K|L]|$I|X|J|Y|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|10|8|@$I|11|J|12|K|L]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|R|$]]

This looks incorrect (and I am unsure how this even compiled):

<pre><code>cout&lt;&lt;v[count]-&gt;getName&lt;&lt;endl;
cout&lt;&lt;v[count]-&gt;getNumber&lt;&lt;endl; 
</code></pre>

as <code>getName</code> and <code>getNumber</code> are methods. Change to:

<pre><code>cout&lt;&lt;v[count]-&gt;getName()&lt;&lt;endl;
cout&lt;&lt;v[count]-&gt;getNumber()&lt;&lt;endl;
</code></pre>

Additionally, the initialisation of <code>count</code> is not posted: ensure it is zero.

blocks|key|2290105|text|那么，您的示例与多态性无关。这里的原因是您没有使用任何虚拟函数。以下是您可以使用的代码。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2290106|class+Item
{
protected:

++++std::string+model_name;
++++int+item_number;

public:

++++Item();
++++Item(std::string&+name,+int+number)+:+model_name(name),+item_number(number)+{};
++++std::string+getName(){return+model_name;}
++++int+getNumber(){return+item_number;}
};

class+Bed+:+public+Item
{
private:

++++std::string+frame;
++++std::string+frameColour;
++++std::string+mattress;

public:

++++Bed();

++++Bed(int+number,+std::string&+name,+std::string&+frm,+std::string&+fclr,+std::string&+mtres)+:+Item(name,+number),+
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++frame(frm),
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++frameColour(fclr),+
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++mattress(mtres)+{};
};

int+main()
{
++++int+count+=+0;
++++std::vector<Item*>+v;

++++Item*+item+=+new+Bed(2,+std::string("MyBed"),+std::string("wood"),+std::string("red"),+std::string("soft"));
++++std::cout+<<+"working,+new+bed"+<<+std::endl;
++++v.push_back(item);

++++std::cout+<<+"working+pushback"+<<+std::endl;
++++std::cout+<<+"+this+is+whats+been+stored:"+<<+std::endl;
++++std::cout+<<+v[count]->getName()+<<+std::endl;
++++std::cout+<<+v[count]->getNumber()+<<+std::endl;

++++%2B%2Bcount;

++++getchar();
}++++|code-block|syntax|javascript|2290107|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Well, you example is not related to polymorphism. The reason here is that you are not using any virtual functions. Here is the code that you can use.

<pre><code>class Item
{
protected:

 std::string model_name;
 int item_number;

public:

 Item();
 Item(std::string&amp; name, int number) : model_name(name), item_number(number) {};
 std::string getName(){return model_name;}
 int getNumber(){return item_number;}
};

class Bed : public Item
{
private:

 std::string frame;
 std::string frameColour;
 std::string mattress;

public:

 Bed();

 Bed(int number, std::string&amp; name, std::string&amp; frm, std::string&amp; fclr, std::string&amp; mtres) : Item(name, number), 
 frame(frm),
 frameColour(fclr), 
 mattress(mtres) {};
};

int main()
{
 int count = 0;
 std::vector&lt;Item*&gt; v;

 Item* item = new Bed(2, std::string("MyBed"), std::string("wood"), std::string("red"), std::string("soft"));
 std::cout &lt;&lt; "working, new bed" &lt;&lt; std::endl;
 v.push_back(item);

 std::cout &lt;&lt; "working pushback" &lt;&lt; std::endl;
 std::cout &lt;&lt; " this is whats been stored:" &lt;&lt; std::endl;
 std::cout &lt;&lt; v[count]-&gt;getName() &lt;&lt; std::endl;
 std::cout &lt;&lt; v[count]-&gt;getNumber() &lt;&lt; std::endl;

 ++count;

 getchar();
} 
</code></pre>

My code compiles fine but I am having issues with a particular section not displaying the correct output.

Here is my base class

<pre><code>class Item
 {
 protected:

//int count;
string model_name;
int item_number;

 public:

Item();
Item(string name, int number);
 string getName(){return model_name;}
int getNumber(){return item_number;}
</code></pre>

and here is my derived class:

<pre><code> class Bed : public Item
 {
 private:

string frame;
string frameColour;
string mattress;

 public:

 Bed();

 Bed(int number, string name, string frm, string fclr, string mtres);
</code></pre>

Function definitions:

<pre><code> Bed::Bed(int number, string name, string frm, string fclr, string mtres)
{
model_name=name;
item_number=number;
frame=frm;
frameColour=fclr;
mattress=mtres;
cout&lt;&lt;model_name&lt;&lt;item_number&lt;&lt;frame&lt;&lt;frameColour&lt;&lt;mattress&lt;&lt;endl;
}
</code></pre>

Main section that is causing the problem:

<pre><code> Item* item= new Bed(number, name, material, colour, mattress);
 cout&lt;&lt;"working, new bed"&lt;&lt;endl;
 v.push_back(item);
 cout&lt;&lt;"working pushback"&lt;&lt;endl;
 cout&lt;&lt;" this is whats been stored:"&lt;&lt;endl;
 cout&lt;&lt;v[count]-&gt;getName&lt;&lt;endl;
 cout&lt;&lt;v[count]-&gt;getNumber&lt;&lt;endl;
 count++;
</code></pre>

when the programme executes, the cout within the constructor shows the correct output, but when I call getname and getnumber from the main function the programme prints '1' for both , no matter what's stored in there.
I thought that derived classes could use base class methods, what have I missed?
Any help would be great

thanks 
Hx

Polymorphism constructor function

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我的代码编译得很好，但我遇到了某个特定部分无法显示正确输出的问题。下面是我的基类class Item { protected://int count;string model_name;int item_number; public:Item();Item(string name, int number);     s...

问多态构造函数
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