Thread: double astrix pointer question..

what this function does?

Double astrix says that the parameter is the pointer which P points at
so the parameters is p->next and num.
They create a node called elt ,they assign it a memory space in a size node
and make it a node pointer.
next they say that elt->next=p->next
elt->value is num
and p->next=elt


I cant imagine what is the structure of the combination of those to marked red lines.
??

Code:

typedef struct node {
    int value;
    struct node *next;
}Node;

void what1(Node ** p,int num){
   Node *elt;
   elt=(Node*)malloc(sizeof(Node));
   elt->next=*p;
   elt->value=num;
   *p=elt;
}

Originally Posted by transgalactic2

what this function does?

Double astrix says that the parameter is the pointer which P points at
so the parameters is p->next and num.

The parameter is a pointer that points to the pointer which points to a Node. The ** means a pointer to a pointer.
So the parameter is p and num.
There is also a pointer which p points at. Lets call it nodePtr. There is also a node in which nodePtr points to. Lets call it node.

You have this:
p -> nodePtr -> node

So:
elt-> next = *p means: elt->next = nodePtr
*p = elt means: nodePtr = elt

Originally Posted by audinue

pass by reference anyone?

In C?

What I think you want is

Code:

(*p)->next

If I understand you correctly.

I think EVOEx is on the mark if I understand your question. p is a pointer to pointer to a Node while *p is a pointer to a Node object as in

Code:

elt->next=(*p)->next 
(*p)->next=elt

what means Node **p in the signature??

p->next ?(a pointer which points to a pointer)

am i correct?

p isn't the same as p->next if that is what you mean. I answered what p means in post #3.

It is indeed a pointer that point to a pointer. So its value (*p) is a pointer that points to a node. So p points to a pointer which pointer points to a node.

so **p point to a Node * type variable

what point to what during this function (in every step)

??

but what is the stucture of **p regarding a linked list system.

I cant imagine what points to what in every step during the running of this function.

Code:

typedef struct node {
    int value;
    struct node *next;
}Node;

void what1(Node ** p,int num){
   Node *elt;
   elt=(Node*)malloc(sizeof(Node));
   elt->next=*p;
   elt->value=num;
   *p=elt;
}

I dont know what it does.
I was asked to explain what it does.
i can guess but this doble astrix thing and linked list
i dont know whats happening in the linked list when the double astrix involved.

Code:

typedef struct node {
    int value;
    struct node *next;
}Node;

void what1(Node ** p,int num){
   Node *elt;
   elt=(Node*)malloc(sizeof(Node));  //create a node called elt ,assign it some memory
   elt->next=*p;     //from this point i dont know what the effect of the double astrix
   elt->value=num;
   *p=elt;
}