1

我是董事会的新成员。我正在使用 MS VS2008。我正在学习列表列表。我正在尝试将元素添加到列表中的列表中。

我在我的程序中指出了我遇到问题的地方。当我调试它时，“beth”被添加到第二个列表（division2），但是当循环退出时，“beth”不在第二个列表中，即使我已经在嵌套循环之外声明了我的所有列表。

任何帮助将不胜感激。

这是代码：

struct item
{
string name;
int age;
};
int main()
{
list<item> division1;
list<item> division2;

list< list<item> >WholeCompany;

item s; 
s.name="sandra"; s.age=43; division1.push_back(s);
s.name="Marc"; s.age=19; division2.push_back(s);
s.name="betty"; s.age=34;division2.push_back(s);

WholeCompany.push_back(division1);
WholeCompany.push_back(division2);

list< list<item> >::iterator WholCompIter;
list<item>::iterator itemIter;

for ( WholCompIter = WholeCompany.begin(); WholCompIter != WholeCompany.end();      WholCompIter++ )
    {
    //incorrect
    //list<item> listEntry = *WholCompIter;
    //instead use:
    list<item> listEntry = *WholCompIter;

    for ( itemIter = listEntry.begin(); itemIter != listEntry.end(); itemIter++ )
    {   
        //MY ISSUE IS RIGHT HERE! How can I add the value to the list, but      the list forgets it when it exit loop
        if(itemIter->name =="betty")
        {
            item s; s.name="beth"; s.age=65;
            listEntry.insert(itemIter,s);//problem is here.
                            //I have also tried
                            //listEntry.push_back(s) but the output doesn't show it

        }
    }
}
    //incorrect. 
//for(list<item>::iterator i=division2.begin(); i!=division2.end();++i)
//  cout<<i->name<<" "<<i->age<<endl;
    //instead use:
    for ( WholCompIter = WholeCompany.begin(); WholCompIter != WholeCompany.end(); WholCompIter++ )
{
    list<item>listEntry = *WholCompIter;

    for ( itemIter = listEntry.begin(); itemIter != listEntry.end(); itemIter++ )
    {   
    cout<<itemIter->name<<" "<<itemIter->age<<endl; 

    }
    cout<<endl; cout<<endl;
}
return 0;
}
4

2 回答 2

2

你只是在这里创建一个副本：

list<item> listEntry = *WholCompIter;

相反，您需要一个参考：

list<item>& listEntry = *WholCompIter;

此外，您正在从division2底部的循环中打印。请记住，这WholeCompany只是division2初始化时的副本。由于您已经WholeCompany通过上面的参考进行了修改，因此您需要WholeCompany在底部的输出循环中访问。

于 2012-07-30T05:11:14.697 回答
1

使固定。

for ( WholCompIter = WholeCompany.begin(); WholCompIter != WholeCompany.end();      WholCompIter++ )
    {
    list<item>& listEntry = *WholCompIter;

    for ( itemIter = listEntry.begin(); itemIter != listEntry.end(); itemIter++ )
    {   
        //MY ISSUE IS RIGHT HERE! How can I add the value to the list, but      the list forgets it when it exit loop
        if(itemIter->name =="betty")
        {
            item s; s.name="beth"; s.age=65;
            listEntry.insert(itemIter,s);//problem is here.
                            //I have also tried
                            //listEntry.push_back(s) but the output doesn't show it

        }
    }
}

当您键入list<item> listEntry时创建局部变量，然后在代码中将其分配给返回值的副本list<list<item>>::iterator::operator *，当您更改它时，对您的list WholeCompany.

在字符串中

WholeCompany.push_back(division1);
WholeCompany.push_back(division2);

您推入and的wholeCompany 副本，因此，当您更改 contains of 、 contains of或will not changed 时。division1division2WholeCompanydivision1division2

于 2012-07-30T05:11:46.233 回答