(OT)
* Badra wrote on Fri, Apr 18, 2008 at 17:03 +0200:
> I have also unsigned char B that stores a binary value. I need to
> convert it to hexadecimal, I do:
>
> char *table = "0123456789abcdef";
> int i;
> for (i=0; i<strlen(B); i++)
> {
> B[2*i+1] = table[B[i] & 0xf];
> B[2*i] = table[(B[i] & 0xf0) >> 4];
> }
>
> The above two converts work correctly.
Sure?
You have a `unsigned char B', that usually is a 8 bit value and
invoke strlen on it? Do you mean a `const unsigned char*'
pointing to binary data?
Still, it would convert excluding first 0x00 byte. But I think it
is worse than that.
------------------------------------------------------------------->8=======
1 #include <stdio.h>
2 #include <assert.h>
3
4 int
5 main(void)
6 {
7 unsigned int guard = 0xdeadbeef;
8 const unsigned char B[] = { 0x01, 0x02, 0x03, 0x04, 0x05, 0x06,
0x00, 0xff };
9 char *table = "0123456789abcdef";
10 int i;
11 for (i=0; i<strlen(B); i++)
12 {
13 B[2*i+1] = table[B[i] & 0xf];
14 B[2*i] = table[(B[i] & 0xf0) >> 4];
15 }
16 assert(guard == 0xdeadbeef);
17 return 0;
18 }
=======8<-------------------------------------------------------------------
# gcc -ggdb x2.c
x2.c: In function `main':
x2.c:13: warning: assignment of read-only location
x2.c:14: warning: assignment of read-only location
# gdb a.out
(gdb) b 12
Breakpoint 1 at 0x80483d7: file x2.c, line 12.
13 B[2*i+1] = table[B[i] & 0xf];
(gdb) p /x guard
$1 = 0xdeadbeef
(gdb) p /x [EMAIL PROTECTED](B)
$2 = {0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x0, 0xff}
(gdb) cond 1 (i>7)
(gdb) c
Continuing.
Breakpoint 1, main () at x2.c:13
13 B[2*i+1] = table[B[i] & 0xf];
(gdb) p /x guard
$3 = 0x31333333
(gdb) p /x [EMAIL PROTECTED](B)
$4 = {0x30, 0x31, 0x33, 0x31, 0x33, 0x33, 0x33, 0x31}
here, the stack already is overflowed. strlen(i) is something undefined
because no EOS zero anywhere in B.
(beside the fact that B contains wrong data, I think
0x30, 0x31, 0x30, 0x32, 0x30, 0x33, .... was intended)
(gdb) d 1
(gdb) c
Continuing.
Program received signal SIGSEGV, Segmentation fault.
0x400969b0 in strlen () from /lib/i686/libc.so.6
0x400969b0 in strlen () from /lib/i686/libc.so.6
(gdb) up
#1 0x080483cd in main () at x2.c:11
11 for (i=0; i<strlen(B); i++)
(gdb) p &B
$5 = (const unsigned char (*)[8]) 0x33333323
oki,
Steffen
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