🔒 Locked

Arrays are EVIL

Started by daviangel Apr 3, 2008 at 1:45 AM 5 replies 2.2k views

Original Post

Apr 3, 2008 at 1:45 AM

I guess I never really understood how bad they were until I came across this evil looking code brushing up on my C:


/* 
   pointers and multidimensional arrays
*/

#include <stdio.h>

int main(void)
{
  int zippo[4][2] = { {2,4}, {6,8}, {1,3}, {5, 7} };

  printf("  zippo = %p, zippo + 1 = %p\n",
            zippo, zippo + 1);
  printf("zippo[0] = %p, zippo[0] + 1 = %p\n",
          zippo[0],  zippo[0] + 1);
  printf(" *zippo = %p, *zippo + 1 = %p\n",
           *zippo,  *zippo + 1);
  printf("zippo[0][0] = %d\n", zippo[0][0]);
  printf(" *zippo[0] = %d\n", *zippo[0]);
  printf("  **zippo = %d\n", **zippo);
  printf("    zippo[2][1] = %d\n", zippo[2][1]);
  printf("*(*(zippo+2) + 1) = %d\n", *(*(zippo+2) + 1));
  printf("*(zippo[2] + 1) = %d\n", *(zippo[2] + 1));

  return 0;
}

I guess I never did have a really good understanding of arrays in the first place since it took me quite a while to decipher this evilness too!

LackOfGrace

Apr 3, 2008 at 1:48 AM

arrays arent evil
uncommented badly-written code is evil :)

Antheus

Apr 3, 2008 at 3:49 AM

There's absolutely nothing evil about the above code.

It merely demonstrates multi-dimensional array memory layout, pointer arithmetic and pointer dereferencing.

DeadXorAlive

Apr 3, 2008 at 4:12 AM

Well it helps if you realize that arrays are little more than pointers to blocks of memory, then this code isn't so evil anymore :)

ToohrVyk

Apr 3, 2008 at 4:14 AM

Quote:
Original post by DeadXorAlive
Well it helps if you realize that arrays are little more than ~~pointers to~~ blocks of memory, then this code isn't so evil anymore :)

There, corrected your post for you [smile]

DeadXorAlive

Apr 3, 2008 at 7:29 AM

Quote:
Original post by ToohrVyk
Quote:
Original post by DeadXorAlive
Well it helps if you realize that arrays are little more than ~~pointers to~~ blocks of memory, then this code isn't so evil anymore :)

There, corrected your post for you [smile]

Oh ok thanks. I was typing this with the 'arrays decay to pointers' thing in mind.

MaulingMonkey

Apr 3, 2008 at 7:55 AM

Quote:
Original post by DeadXorAlive
Quote:
Original post by ToohrVyk
Quote:
Original post by DeadXorAlive
Well it helps if you realize that arrays are little more than ~~pointers to~~ blocks of memory, then this code isn't so evil anymore :)

There, corrected your post for you [smile]

Oh ok thanks. I was typing this with the 'arrays decay to pointers' thing in mind.

The decay part is important -- when people forget this, they do things like cast a int[4][2]* to an int*** and expect it to work.

(void*)array   == (void*)&array, typically(void*)pointer != (void*)&pointer, typically

None of this was touched upon in the relatively tame originally posted snippet ;-)

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.