PROGRAMMING - Hacking: The Art of Exploitation - page 99

printf("bytes of struct located at 0x%08x\n", time_ptr);
raw_ptr = (unsigned char *) time_ptr;
for(i=0; i < size; i++)
{
printf("%02x ", raw_ptr[i]);
if(i%16 == 15) // Print a newline every 16 bytes.
printf("\n");
}
printf("\n");
}
int main() {
long int seconds_since_epoch;
struct tm current_time, *time_ptr;
int hour, minute, second, i, *int_ptr;
seconds_since_epoch = time(0); // Pass time a null pointer as argument.
printf("time() - seconds since epoch: %ld\n", seconds_since_epoch);
time_ptr = &current_time; // Set time_ptr to the address of
// the current_time struct.
localtime_r(&seconds_since_epoch, time_ptr);
// Three different ways to access struct elements:
hour = current_time.tm_hour; // Direct access
minute = time_ptr->tm_min; // Access via pointer
second = *((int *) time_ptr); // Hacky pointer access
printf("Current time is: %02d:%02d:%02d\n", hour, minute, second);
dump_time_struct_bytes(time_ptr, sizeof(struct tm));
minute = hour = 0; // Clear out minute and hour.
int_ptr = (int *) time_ptr;
for(i=0; i < 3; i++) {
printf("int_ptr @ 0x%08x : %d\n", int_ptr, *int_ptr);
int_ptr++; // Adding 1 to int_ptr adds 4 to the address,
} // since an int is 4 bytes in size.
}
The results of compiling and executing time_example2.c are as follows.
reader@hacking:~/booksrc $ gcc -g time_example2.c
reader@hacking:~/booksrc $ ./a.out
time() - seconds since epoch: 1189311744
Current time is: 04:22:24
bytes of struct located at 0xbffff7f0
18 00 00 00 16 00 00 00 04 00 00 00 09 00 00 00
08 00 00 00 6b 00 00 00 00 00 00 00 fb 00 00 00
00 00 00 00 00 00 00 00 28 a0 04 08
int_ptr @ 0xbffff7f0 : 24
int_ptr @ 0xbffff7f4 : 22
int_ptr @ 0xbffff7f8 : 4
r eader@hacking:~/booksrc $