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digitalmars.D - Get object address when creating it in for loop

reply "hardcoremore" <caslav.sabani gmail.com> writes:
How to get and address of newly created object and put it in 
pointer array?


int maxNeurons = 100;
Neuron*[] neurons = new Neuron*[](maxNeurons);

Neuron n;

for(int i = 0; i < maxNeurons; i++)
{
         n = new Neuron();
	neurons[] = &n; // here &n always returns same adress
}

writefln("Thread func complete. Len: %s", neurons);


This script above will print array with all the same address 
values, why is that?


Thanks
May 05 2014
next sibling parent "Adam D. Ruppe" <destructionator gmail.com> writes:
On Monday, 5 May 2014 at 16:15:43 UTC, hardcoremore wrote:
 	neurons[] = &n; // here &n always returns same adress

You're taking the address of the pointer, which isn't changing. Just use plain n - when you new it, it is already a pointer so just add that value to your array.
May 05 2014
prev sibling next sibling parent Nick Sabalausky <SeeWebsiteToContactMe semitwist.com> writes:
On 5/5/2014 12:15 PM, hardcoremore wrote:
 How to get and address of newly created object and put it in pointer array?


 int maxNeurons = 100;
 Neuron*[] neurons = new Neuron*[](maxNeurons);

 Neuron n;

 for(int i = 0; i < maxNeurons; i++)
 {
          n = new Neuron();
      neurons[] = &n; // here &n always returns same adress
 }

 writefln("Thread func complete. Len: %s", neurons);


 This script above will print array with all the same address values, why
 is that?


 Thanks

These sorts of questions should go in digitalmars.D.learn, but your problem is a simple typo here: neurons[] = &n; That sets the *entire* array to "&n". You forgot the index: neurons[i] = &n;
May 05 2014
prev sibling next sibling parent "Caslav Sabani" <caslav.sabani gmail.com> writes:
Hi Guys,


Thanks so much for your reply. This fixes my problem like Adam D.
Ruppe suggested:

int maxNeurons = 100;
Neuron[] neurons = new Neuron[](maxNeurons);

Neuron n;

for(int i = 0; i < maxNeurons; i++)
{
	n = new Neuron();
	neurons[] = n;
}

But can you give me a more details so I can understand what is
going on. What is the difference between

Neuron[] neurons = new Neuron[](maxNeurons);

and

Neuron*[] neurons = new Neuron*[](maxNeurons);


As I understand Neuron*[] should create array which elements are
pointers?


Is it possible to instantiate 100 objects in a for loop and get a
address of each object instance and store it in array of pointers?



Thanks
May 05 2014
prev sibling next sibling parent Jonathan M Davis via Digitalmars-d <digitalmars-d puremagic.com> writes:
On Mon, 05 May 2014 16:15:42 +0000
hardcoremore via Digitalmars-d <digitalmars-d puremagic.com> wrote:

 How to get and address of newly created object and put it in
 pointer array?


 int maxNeurons = 100;
 Neuron*[] neurons = new Neuron*[](maxNeurons);

 Neuron n;

 for(int i = 0; i < maxNeurons; i++)
 {
          n = new Neuron();
   neurons[] = &n; // here &n always returns same adress
 }

 writefln("Thread func complete. Len: %s", neurons);


 This script above will print array with all the same address
 values, why is that?

&n gives you the address of the local variable n, not of the object on the heap that it points to. You don't normally get at the address of class objects in D. There's rarely any reason to. Classes always live on the heap, so they're already references. Neuron* is by definition a pointer to a class _reference_ not to an instance of Neuron. So, you'd normally do Neuron[] neurons; for your array. I very much doubt that you really want an array of Neuron*. IIRC, you _can_ get at an address of a class instance by casting its reference to void*, but I'm not sure, because I've never done it. And even then, you're then using void*, not Neuron*. Also FYI, questions like this belong in D.learn. The D newsgroup is for general discussions about D, not for questions related to learning D. - Jonathan M Davis
May 05 2014
prev sibling parent "Caslav Sabani" <caslav.sabani gmail.com> writes:
Hi Jonathan,



Thanks for your reply. So actually I was getting the pointer of n 
itself.

I understand now what was my problem. The problem was that I did 
not know that array support references of objects, so I thought 
that I must fill it with pointers of objects.

But its great that I do not have to use pointers :)



Thanks a lot.
May 05 2014