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POINTERS AND ARROW

Posted on 2003-10-31
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Last Modified: 2010-04-02
please help me understand how pointers work and how this works "->" .  i really dont understand these concepts and i need step by step explanation of what they mean.  here are examples:


Struct Node { int data; Node *next;}; Node *p1, *p2, *p3;

p1->data = 112;//please explain this step
p2->data = 55;
*p1 = *p2; //please explain this step

cout << p1->data << "  " << p2->data<<endl;

the result of the cout is 55 55 but please help me step step explanation on how it works.
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Question by:needle176
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by:AmitAgarwal
ID: 9661768
pointer is actually a address where the data is stored.
so if you say p1 is a pointer to struct Node it means it is pointing to the address where Node is created.
-> is mechanism to access the members of structure or class using pointers.

so p1->data = 112;
means p1 is pointing to a node structure and that structure has a variable called data and you are assigning 112 to that variable.

*p1 = *p2; //please explain this step

p2 is pointing to another structure whose value you have set to 55.
so when you say
*p1 = *p2;
it copies the content of one structure into another
so now p1 Node will be initialized with the values in p2 node.
thats why you are getting both the values as 55

amit
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tinchos earned 20 total points
ID: 9661780
The concept of pointer is the following..................

you have an object (or struct, or built in type)...... stored in some place in memory...........

a pointer to an object is just the memory address where that object is stored..............

imagine that p is a pointer that points to an object (lets call it a)

then *p is the object that the pointer is pointing to (a itself)
and p->something is the same than to call a.something

this means, it's like to call some method or variable of the object to which the pointer is pointing to

Struct Node { int data; Node *next;}; Node *p1, *p2, *p3;        // In this line you declare 3 pointers (p1, p2, p3) to a struct

// Here you set that the value of the "data" member of the object pointed by p1 is equal to 112
p1->data = 112;//please explain this step                    
// Here you set that the value of the "data" member of the object pointed by p2 is equal to 55
p2->data = 55;

// Here you set that the value of the "data" member of the object pointed by p1 is equal to the value of the "data" member of the object pointed by p2 (this is 55)
*p1 = *p2; //please explain this step

// You print the 2 data members, that are both 55 (see the step before)
cout << p1->data << "  " << p2->data<<endl;

Hope it was clear enoughj

Tincho
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