Trouble with pointers..

[saurav2007]

Hi i got some problems with c pointers...feelin trouble to get through it..here is a problem .anyone plz explain the solutin to me..

#include<stdio.h>
main()
{
int arr[3]={2,3,4};
char *p=arr;
p=(char*)((int*)(p)); printf("%d",*p);
p=(int*)(p+1); printf("%d",*p); }

[cse.avinash]

char* generally stores the address of char type,here it stores the address of int type.
since char occupy 1 byte memory space while int occupy 2 byte or 4 byte(machine & compiler dependent) space in memory. so on increment in p it will refer to next byte incremented by 1 while the next value is 2 or 4 byte from that address of arr . what I mean to say is that.

Suppose arr has an address of 2000 so p=arr means p has an address of arr.
but arr is of type int so arr[1] will be stored in address 2004.
and on increasing the pointer with value 1 it will point to 2001(as it is of char type) which doesn't contain the value arr[1]. so it will result out 0.

you can refer to arr[1] by :-

p=(int*)(p+2);//if int take 2 bytes
p=(int*)(p+4);//if int take 4 bytes

[saurav2007]

I got u but when i m increasing the address in
p=(char*)((int*)(p)); printf("%d",*p); by 2 or 4 bytes output is 0..

can u explain this too..

[cse.avinash]

p=(char*)((int*)(p+4));
        printf("%d\n",*p);

p=(char*)((int*)(p)); 
      printf("%d\n",*(p+4));

Both increments are working correctly in my compiler giving output 3.
which compiler are you using..??

[gerard4143]

Not sure why your handling your pointer that way? Try writing your program like below:

#include <stdio.h>
#include <stdlib.h>

#define ELEM_POS 2

int main(int argc, char** argv)
{
    int x[] = {1, 2, 3, 4};
    char *p = (char*)x;

    fprintf(stdout, "p->%d\n", *(int*)p);

    p = (char*)(p + sizeof(int) * ELEM_POS);

    fprintf(stdout, "p->%d\n", *(int*)p);
    return (EXIT_SUCCESS);
}

[cse.avinash]

Yup instead of talking like an unprofessional, i should have used sizeof(int) instead.

@gerard4143:-

p = (char*)(p + sizeof(int) * ELEM_POS);

why are you multiplying sizeof(int) with 2.
it will print element of x[2] instead of x[1].

and
what is the use of command line argument here...I didn't understand. Please Explain.:-O

[saurav2007]

@cse.avinash
ya i got u..there was some mistake by me..thanx for the help:)

[cse.avinash]

okay.. keep enjoy programming.. :)