printf conversion problem

[buzzdee]

hi,

i just wanted to print out
some unsigned long int values in hexadecimal,
printing out one value works, but not byte by byte.
anybody has a suggestinon what my problem is?

this is my program:


#include <stdio.h>
#include <stdlib.h>
#include <arpa/inet.h>

#include <stdio.h>
int main (void) {
unsigned long testint = 6070;
unsigned long bigend = htonl(testint);
char *le = (char *) &testint;
char *be = (char *) &bigend;

printf("HO: %08X\n", testint);
printf("NO: %08X\n", bigend);

printf("HO: %02X %02X %02X %02X\n", le[0], le[1], le[2], le[3]);
printf("NO: %02X %02X %02X %02X\n", be[0], be[1], be[2], be[3]);

}

and this is my output:

$ ./test
HO: 000017B6
NO: B6170000
HO: FFFFFFB6 17 00 00
NO: 00 00 17 FFFFFFB6

anybody can tell me why i have that FFFFFFB6 Values in the output wiht
%02X ?

buzz

[Jack Klein]

Re: printf conversion problem

On Sun, 26 Sep 2004 16:54:46 +0200, buzzdee
<reitenba@fh-brandenburg.de> wrote in comp.lang.c:

C has three character types, signed char, unsigned char, and 'plain'
char, the type you get when you don't specify signed or unsigned.
'Plain' char is the same as either signed or unsigned char, but it is
up to the implementation which it is.

In your case, 'plain' char is signed. The value 0xb6 in a char on
your implementation has the value -74. When you pass the value of
that char to printf(), it is converted to an int with the value -74,
which is represented in your implementation as 0xffffffb6.
[color=blue]
> hi,
>
> i just wanted to print out
> some unsigned long int values in hexadecimal,
> printing out one value works, but not byte by byte.
> anybody has a suggestinon what my problem is?
>
> this is my program:
>
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <arpa/inet.h>
>
> #include <stdio.h>
> int main (void) {
> unsigned long testint = 6070;
> unsigned long bigend = htonl(testint);
> char *le = (char *) &testint;
> char *be = (char *) &bigend;[/color]

Change the types, and the casts, of 'le' and 'be' to unsigned char,
instead of just 'plain' char.
[color=blue]
>
> printf("HO: %08X\n", testint);
> printf("NO: %08X\n", bigend);
>
> printf("HO: %02X %02X %02X %02X\n", le[0], le[1], le[2], le[3]);
> printf("NO: %02X %02X %02X %02X\n", be[0], be[1], be[2], be[3]);
>
> }
>
> and this is my output:
>
> $ ./test
> HO: 000017B6
> NO: B6170000
> HO: FFFFFFB6 17 00 00
> NO: 00 00 17 FFFFFFB6
>
> anybody can tell me why i have that FFFFFFB6 Values in the output wiht
> %02X ?
>
> buzz[/color]

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.l earn.c-c++

http://www.contrib.andrew.cmu.edu/~ajo/docs/FAQ-acllc.html

[Flash Gordon]

Re: printf conversion problem

On Sun, 26 Sep 2004 16:54:46 +0200
buzzdee <reitenba@fh-brandenburg.de> wrote:
[color=blue]
> hi,
>
> i just wanted to print out
> some unsigned long int values in hexadecimal,
> printing out one value works, but not byte by byte.
> anybody has a suggestinon what my problem is?
>
> this is my program:
>
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <arpa/inet.h>
>
> #include <stdio.h>
> int main (void) {
> unsigned long testint = 6070;
> unsigned long bigend = htonl(testint);
> char *le = (char *) &testint;
> char *be = (char *) &bigend;[/color]
Try:
unsigned char *le = (unsigned char *) &testint;
unsigned char *be = (unsigned char *) &bigend;[color=blue]
>
> printf("HO: %08X\n", testint);
> printf("NO: %08X\n", bigend);[/color]

According to the man page (my copy of K&R is in the office) %X expects
an unsigned in not an unsigned long. You want
printf("HO: %08lX\n", testint);
printf("NO: %08lX\n", bigend);
You are also assuming that unsigned long is 32 bits, which is not
guaranteed by the standard. This is OK if you want at least 32 bits (I
think), but if you want exactly 32 bits (which from using the
non-standard htonl I guess you do) you might want to use a typedef which
you can set to the appropriate type on each system, including using the
exact width types that are optional in C99 if you use any C99
implementations ,<OT> and the POSIX ones if you use POSIX systems.
Why couldn't C99 have adopted the POSIX fixed width types?</OT>
[color=blue]
> printf("HO: %02X %02X %02X %02X\n", le[0], le[1], le[2],
> le[3]);
> printf("NO: %02X %02X %02X %02X\n", be[0], be[1],
> be[2], be[3]);[/color]

You are assuming that CHAR_BIT==8 and sizeof unsigned int == 4. This
might be true for the systems you care about, but neither is always
true.
[color=blue]
> }
>
> and this is my output:
>
> $ ./test
> HO: 000017B6
> NO: B6170000
> HO: FFFFFFB6 17 00 00
> NO: 00 00 17 FFFFFFB6
>
> anybody can tell me why i have that FFFFFFB6 Values in the output wiht
> %02X ?[/color]

On your system char is obviously signed and your system uses 2s
complement, so it gets promoted to an int using signed extension, i.e.
filling the extra bits with what the sign bit was.
--
Flash Gordon
Sometimes I think shooting would be far too good for some people.
Although my email address says spam, it is real and I read it.

[Martin Ambuhl]

Re: printf conversion problem

buzzdee wrote:
[color=blue]
> hi,
>
> i just wanted to print out
> some unsigned long int values in hexadecimal,
> printing out one value works, but not byte by byte.
> anybody has a suggestinon what my problem is?
>
> this is my program:
>
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <arpa/inet.h>
>
> #include <stdio.h>
> int main (void) {
> unsigned long testint = 6070;
> unsigned long bigend = htonl(testint);
> char *le = (char *) &testint;
> char *be = (char *) &bigend;
>
> printf("HO: %08X\n", testint);
> printf("NO: %08X\n", bigend);
>
> printf("HO: %02X %02X %02X %02X\n", le[0], le[1], le[2], le[3]);
> printf("NO: %02X %02X %02X %02X\n", be[0], be[1], be[2], be[3]);
>
> }
>
> and this is my output:
>
> $ ./test
> HO: 000017B6
> NO: B6170000
> HO: FFFFFFB6 17 00 00
> NO: 00 00 17 FFFFFFB6
>
> anybody can tell me why i have that FFFFFFB6 Values in the output wiht
> %02X ?[/color]

Because you have signed chars:


#include <stdio.h>
#include <stdlib.h>

#include <stdio.h>
int main(void)
{
unsigned long testint = 6070;
unsigned long bigend = 0xb6170000;
unsigned char *le = (unsigned char *) &testint; /* mha: fixed types
*/
unsigned char *be = (unsigned char *) &bigend; /* mha: fixed types
*/

printf("HO: %08lX\n", testint); /* mha: fixed specifier */
printf("NO: %08lX\n", bigend); /* mha: fixed specifier */
if (sizeof(unsigne d long) < 4) {
fprintf(stderr, "Damn!\n");
exit(EXIT_FAILU RE);
}
printf("HO: %02X %02X %02X %02X\n", le[0], le[1], le[2], le[3]);
printf("NO: %02X %02X %02X %02X\n", be[0], be[1], be[2], be[3]);
return 0;
}

[output]

HO: 000017B6
NO: B6170000
HO: B6 17 00 00
NO: 00 00 17 B6