PROGRAMMING - Hacking: The Art of Exploitation - page 57

reader@hacking:~/booksrc $ gcc pointer_types4.c
reader@hacking:~/booksrc $ ./a.out
[char pointer] points to 0xbffff810, which contains the char 'a'
[char pointer] points to 0xbffff811, which contains the char 'b'
[char pointer] points to 0xbffff812, which contains the char 'c'
[char pointer] points to 0xbffff813, which contains the char 'd'
[char pointer] points to 0xbffff814, which contains the char 'e'
[integer pointer] points to 0xbffff7f0, which contains the integer 1
[integer pointer] points to 0xbffff7f4, which contains the integer 2
[integer pointer] points to 0xbffff7f8, which contains the integer 3
[integer pointer] points to 0xbffff7fc, which contains the integer 4
[integer pointer] points to 0xbffff800, which contains the integer 5
r eader@hacking:~/booksrc $
The compilation and output of this pointer_types4.c is basically the same
as that for pointer_types3.c. The void pointer is really just holding the memory
addresses, while the hard-coded typecasting is telling the compiler to use the
proper types whenever the pointer is used.
Since the type is taken care of by the typecasts, the void pointer is truly
nothing more than a memory address. With the data types defined by type-
casting, anything that is big enough to hold a four-byte value can work the
same way as a void pointer. In pointer_types5.c, an unsigned integer is used
to store this address.
pointer_types5.c
#include <stdio.h>
int main() {
int i;
char char_array[5] = {'a', 'b', 'c', 'd', 'e'};
int int_array[5] = {1, 2, 3, 4, 5};
unsigned int hacky_nonpointer;
hacky_nonpointer = (unsigned int) char_array;
for(i=0; i < 5; i++) { // Iterate through the int array with the int_pointer.
printf("[hacky_nonpointer] points to %p, which contains the char '%c'\n",
hacky_nonpointer, *((char *) hacky_nonpointer));
hacky_nonpointer = hacky_nonpointer + sizeof(char);
}
hacky_nonpointer = (unsigned int) int_array;
for(i=0; i < 5; i++) { // Iterate through the int array with the int_pointer.
printf("[hacky_nonpointer] points to %p, which contains the integer %d\n",
hacky_nonpointer, *((int *) hacky_nonpointer));
hacky_nonpointer = hacky_nonpointer + sizeof(int);
}
}