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Update element in list

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Join Date: May 2009

Posts: 20

Reputation: eliza2044 is an unknown quantity at this point

Solved Threads: 0

eliza2044

Offline

Newbie Poster

Update element in list

Oct 22nd, 2009

Hey guys,

Can anyone post sample code about updating an object that is already in an std::list? I know that it sounds as a really stupid question, but obviously I'm doing something wrong.

In my code I'm going through the list with an iterator until I reach the object of interest. My intention is to replace the current node in the list with another object.

The following snippet of code demonstrates that but I'm sure that I do something wrong in the if statement.

Thanks in advance..!

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
bool updateListElement(Object* air)
{
     list <Object>::iterator iObject;
     for (iObject= list.begin(); iObject != list.end(); ++iObject)
     {
        Object temp = *iObject;
        if (temp.getCode() == air->getCode())
        {
            temp=*air;
            return true;
        }
     }
     return false;
}
bool updateListElement(Object* air)
{
     list <Object>::iterator iObject;
     for (iObject= list.begin(); iObject != list.end(); ++iObject)
     {
        Object temp = *iObject;
        if (temp.getCode() == air->getCode())
        {
            temp=*air;
            return true;
        }
     }
     return false;
}

•

Join Date: Jun 2009

Posts: 681

Reputation: Tom Gunn has much to be proud of

Solved Threads: 133

Tom Gunn

Offline

Practically a Master Poster

Oct 22nd, 2009

Close, but a temporary copy of the object is still an independent copy. C++ does not make reference copies of objects like Java or C#. To replace the object the iterator refers to, you need to assign to the dereferenced iterator. This will overwrite the object that it refers to:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
bool updateListElement(Object* air)
{
    std::list <Object>::iterator iObject;
     for (iObject= list.begin(); iObject != list.end(); ++iObject)
     {
        Object temp = *iObject;
        if (temp.getCode() == air->getCode())
        {
            *iObject = *air;
            return true;
        }
     }
     return false;
}
bool updateListElement(Object* air)
{
    std::list <Object>::iterator iObject;
     for (iObject= list.begin(); iObject != list.end(); ++iObject)
     {
        Object temp = *iObject;
        if (temp.getCode() == air->getCode())
        {
            *iObject = *air;
            return true;
        }
     }
     return false;
}

-Tommy (For Great Justice!) Gunn

•

Join Date: May 2009

Posts: 20

Reputation: eliza2044 is an unknown quantity at this point

Solved Threads: 0

eliza2044

Offline

Newbie Poster

Oct 22nd, 2009

Thank you very much... I was trying to figure out what was wrong and never thought I had to do it that way!!!

Well thanks, I need to keep that in mind with C++....!!!!

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