Add object in function to dynamic array of pointers

Question

3.00/5 (2 votes)

See more:

Classes:
Chair;
BigChair; (no innherit)

Chair.h:
int _bigChairsLength;
BigChair** _bigChairs;

Chair.cpp:

C++

void Chair::AddBigchair(string name, string color) // It must get params and not BigChair
{
     BigChair** temp = _bigChairs;
     _bigChairsLength++;
     _bigChairs = new BigChair*[_bigChairsLength];

     for (int i=0; i<_bigChairsLength - 1; i++)
     {
         _bigChairs[i] = temp[i];
     }

     delete [] temp;

     BigChair newBigChair(name, color);
     _bigChairs[_bigChiarsLength - 1] = &newBigChair;
              // (pointer to function variable??? how to add?
}

Posted 22-Nov-13 13:01pm

Member 7966831

Updated 22-Nov-13 13:03pm

v2

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Comments

Sergey Alexandrovich Kryukov 22-Nov-13 19:22pm

Not clear. This is just a code dump. What do you want to achieve?
—SA

Member 7966831 22-Nov-13 19:33pm

Was desctibed in the comment

Andreas Gieriet 24-Nov-13 2:56am

Since you did not care to ask a decent question (you seem not to care to ask with any full sentences - one has to dig deep into the details), your question was voted down, and therefore, most likely no one would take the trouble to read and answer your question. That's how it works.
Make it easy to the readers to answer your questions: Write as first sentences what the situation is, what you did try out so far, and where you struggle. Then only comes the code.
Cheers
Andi

Member 7966831 24-Nov-13 18:53pm

Sure.

1 solution

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Andreas Gieriet · Accepted Answer · 2013-11-22T13:21:00

Solution 1

Your new array gets a pointer of a local variable (an element from the stack instead of from the heap). That variable gets destroyed and the pointer points to garbage. In fact, it points to some memory that will eventually hold other data and you will severly corrupt the program memory - unpredictable crash sooner or later...
Fix:

C++

_bigChairs[_bigChiarsLength - 1] = new BigChair(name, color);

Is this a homweork assignment or an interview question? This is so basic.
Cheers
Andi

PS: use a suitable STL container (e.g. a vector) instead of a pointer of pointer. E.g. std::vector<BigChair> (or std::vector<BigChair*>, depends on you usage). The whole function would collaps to mvVector.push_back(BigChair(name, color));.

Posted 22-Nov-13 13:21pm

Andreas Gieriet

Updated 22-Nov-13 13:26pm

v3

Comments

Member 7966831 22-Nov-13 19:32pm

Thanks for your reply.
But how is it that you add an object instead of pointer to the array?
It is defined as BigChair**

Andreas Gieriet 24-Nov-13 3:01am

You obviously implement a container. Why re-inventing the wheel? Use the standard library containers (e.g. a vector) instead. And as I said, dependeing on your application, you might add an object instead of a pointer to an object. You say you have no polymorphism, so an object would do.
Cheers
Andi

Member 7966831 24-Nov-13 18:51pm

The issue was I didn't know 'new' operator return a pointer and not an object. Now it makes sense, thanks.

Andreas Gieriet 25-Nov-13 4:09am

You really have to be aware of the difference between Java/C# and C/C++ when it comes to memory management, especially the difference of new between Java/C# and C++.
Cheers
Andi