Array of Objects Initialization (C++)

Question

Hey guys i am i am new to C++ and through to a project i have in the university i am having some difficult times . More spesificaly : i ve created a code for Lists and Queues (Lists name = Chain , Queues name = Queue , Product is a struct that has basicly Chains fields) [btw i ve used Sahnis book (data structures) if anyone knows it. I am stuck here :

int k=4;
Queue<Chain<Product>*>* x = new Queue<Chain<Product>*> [k];
for(int i=1;i<k;i++)
{
   x[i] = new Queue<Chain<Product>*> [i+1];
}

on the loop it throws me error : Invalid conversion from Queue*>* to int

Any idea?

Using a vector (or even a normal array) instead of pointer array will help too. — Qaz
– Qaz, Commented May 3, 2012 at 20:13

Luchian Grigore · Accepted Answer · 2012-05-03 20:13:19Z

2

It should be

for(int i=0;i<k;i++)   // first index is 0
{
   x[i] = Queue<Chain<Product>*>();
}

because

Queue<Chain<Product>*>* x = new Queue<Chain<Product>*> [k];

creates an array of Queue<Chain<Product>*> objects, not pointers.

Or if you want a 2-d array, you use:

Queue<Chain<Product>*>** x = new Queue<Chain<Product>*> * [k];
for(int 0=1;i<k;i++)
{
   x[i] = new Queue<Chain<Product>*> [i+1];
}

To simplify, you're basically attempting the following:

int* x = new int[4];
for ( int i = 0 ; i < 4 ; i++ )
   x[i] = new int[i];

which is obviously wrong.

answered May 3, 2012 at 20:13

Luchian Grigore

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7 Comments

user1241335 Over a year ago

Btw, I don't remember if it's doable in C++ (I work in C# and Java mainly) but can't Queue<Chain<Product>*> have a static function .operator[int x]? It's obviously not the case here, but just asking.

Luchian Grigore Over a year ago

@Shingetsu yes, it's possible to overload operators, but I don't see the point of having a static operator[].

user1241335 Over a year ago

I mean is it possible to overload an operator to be static? And if it could exist it might be used to retrieve an decoded version of the class from a certain file location or similar, those are details.

Luchian Grigore Over a year ago

@Shingetsu I don't think it's possible, and again, it wouldn't make sense.

Menelaos Kotsollaris Over a year ago

Now the code compiles , but when i run it windows pop a message that says : filename.exe stoped executing . Note that the same thing was happening without the for loop!

|

user1241335 · Accepted Answer · 2012-05-03 20:13:49Z

1

In the line x[i] = new Queue<Chain<Product>*> [i+1] he [i+1] is wrong.
Why? Well you're creating a new object new keyword. and .operator[int x] is used in arrays. In that line you are saying it should be a new Array of size i+1 of type Queue<Chain<Product>*> which is faulty. Instead use x[i] = Queue<Chain<Product>*>();

So end code is:

for(int i=0;i<k;i++)//because indexes begin at 0, not 1.
{
  x[i] = Queue<Chain<Product>*>()
}

Note* to see a simplified version of your mistake, see other guy's post (I won't copy code around - wastes space).

answered May 3, 2012 at 20:13

user1241335

3 Comments

Menelaos Kotsollaris Over a year ago

Thank you for your help . when i run it it compliles perfect , however windows pop up an error when i run it that says that filename.exe stoped exececuting. Without the for loop it pops the same thing wich means that i still havent saved space for my array. Simply with my old code id didnt compile cause i had several mistakes but if i hadnt the for loop , the result is the same one with your code

user1241335 Over a year ago

@Tryme_34 it's not linked with this. Stopped executing doesnt always mean run out of memory, my guess is it's an error later in the code. Post a new question with full source.

Menelaos Kotsollaris Over a year ago

yeah i will post tomorrow , but keep in mind that my code compiles and run okay without the initialization and when i add this code windows pop up the message I will create a full topic tomorrow thanks for the help!

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