Convert from hex to dec

Ephracis · 05-30-2005, 06:26 AM

I have been googling the entire lesson and for some reason everything I try fails.

I have a program that uses a memory address. I used to read this from the stack pointer but now I want to be able to type the address from the command line, as an argument to the program.

Now, this address is stored in a long, but how can I convert from the string argument to a long? Here goes the program in some pseudo code:

Code:

unsigned long getsp() {
      __asm__("movl %esp,%eax");
}

int main(int argc, char *argv[]) {

/* used this before, it shows the address of esp */
      long sp = getsp();
      printf("sp: 0x%x (%f)\n", sp, sp);

/* want to read from argument sent to program */
      long new = convert_from_hex_to_long(argv[1]);
      same printf as before;

}

Regards.

jim mcnamara · 05-30-2005, 06:35 AM

use strtol() to convert a string from hex to a long

Ephracis · 05-30-2005, 08:17 AM

Quote:

Originally posted by jim mcnamara
use strtol() to convert a string from hex to a long

Already tried, here is why it fails:

An address is 8 'characters' long, the problem is that it works with up tp 7, then something strange happens:

Code:

$ cat convert.c
#include <stdlib.h>
#include <stdio.h>

unsigned long getsp() {
        __asm__("movl %esp,%eax");
}

int main(int argc, char *argv[]) {

/* used this before, it shows the address of esp */
        unsigned long sp = getsp();
        printf("sp: 0x%x (%d)\n", sp, sp);

/* want to read from argument sent to program */
        unsigned long test = strtol(argv[1], 0, 16);
        printf("test: 0x%x (%d)\n", test, test);
}
$ ./convert b 
sp: 0xbffff568 (-1073744536)
test: 0xb (11)
$ ./convert bf
sp: 0xbffff568 (-1073744536)
test: 0xbf (191)
$ ./convert bfff
sp: 0xbffff568 (-1073744536)
test: 0xbfff (49151)
$ ./convert bffff55
sp: 0xbffff568 (-1073744536)
test: 0xbffff55 (201326421)
$ ./convert bffff558
sp: 0xbffff558 (-1073744552)
test: 0x7fffffff (2147483647)

With the last one the long flips over, but it's decimal value is 16 less then the value of sp, so why can sp be stored but not the address I typed in?
Any ideas?

Harmaa Kettu · 05-30-2005, 10:42 AM

strtol() returns a (signed) long, and 0xbffff558 is out of range for that. Try strtoul(), which returns an unsigned long.