Programming

Question

Can anybody explain these two statements with some example? I am unable to get the difference between them

1) An array, each element of which is a pointer to a structure of type node

B) A structure of 2 fields, each field being a pointer to an array of 10 elements

Need a clear explaination

Comments

For 1)

struct node{

int data;

struct node *left;

struct node *right;

};

struct node *n[20];

Here, n is an array (as in C, [] has higher precedence than *) of 20 elements,  each being a pointer to a structure of type node.

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for 2)

the data type of array is not mentioned, assuming it to be int, it will look like,

struct Node{

int (*p)[10];

int (*q)[10]; 

};

here () and [] both have same precedence but both are left associative, therefore (*p) will be first evaluated as a pointer which will then point to integer array,

in whole above declaration will be termed as "p and q are pointers pointing to an integer array of 10 elements"

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@joshi_nitish, if we have a structure of n fields each being a pointer to an array of 10 elements, do we have to make this declaration "n times" ? or is there any efficient method ??

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you can do it like this,

int (*(*p)[20])[10];

it is termed as "p is a pointer to an array of 20 pointers pointing  to an integer array of 10 elements"

see, you can use 20 differnt pointer to an array of 10 elements..

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Good read:- http://www.geeksforgeeks.org/complicated-declarations-in-c/

I have followed this article and able to solve most of the questions related to this concept

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@nitish

why do we need 2 pointer of each element?

I mean single array element doesnot need 2 pointers

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@srestha

i am not getting what you want to ask..

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"p is a pointer to an array of 20 pointers pointing  to an integer array of 10 elements"

that means each element of array takes 2 elements on average.

why do we need 2 pointer of each element?

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@srestha,
suppose you want to declare 20 different pointers which should point to an arrays, now one way is to declare 20 different pointers individually or simply do above declaration..

also dont confuse with the fact that all 20 pointers are pointing to same array, they are just declaration(not yet pointing to any array), all 20 pointers can be made to point different arrays later..