damn it...gdb and c

alaios · 08-25-2005, 01:32 AM

OKAY now i am crazy......

I have written a small prog in c .. before the program exits prints the following message
printf("Now the buffer is %s \n",buffer);

Now the buffer is line1
line2 (line 3 is blank)line4line5line6

When i use the gdb i use run and the programme ends succesfully i type
p buffer (print buffer)
and this gives me the following

(gdb) print buffer
$1 = "line1\nline2 (line 3 is blank\nline4\n\nline5\n\nline6\000\000"

as u can see my string has many \n characters but i dont know why at the first case are ignored

itsme86 · 08-25-2005, 10:09 AM

Well, it's kind of hard to say why you're getting anything without seeing your code.

paulsm4 · 08-25-2005, 02:29 PM

Another question: are you really getting "\n" (a 1-byte newline character), or are you actually getting the two characters "\", followed by "n"????

Here's my test program:

Code:

#include <stdio.h>

int
main (int argc, char *argv[])
{
  char *s = "line1\nline2 (line 3 is blank\nline4\n\nline5\n\nline6)";
  return printf ("s: %s.\n", s);
}

Here's the compile and ouput:

Code:

% gcc -g -o x x.c
% ./x
s: line1
line2 (line 3 is blank
line4

line5

line6).

And here's the Gcc output (edited for clarity):

Code:

(gdb) p s
$1 = 0x8048518 "line1\nline2 (line 3 is blank\nline4\n\nline5\n\nline6)"
(gdb) x/10x s
0x8048518 :  0x656e696c      0x696c0a31      0x2032656e     0x6e696c28
0x8048528 :  0x20332065      0x62207369      0x6b6e616c     0x6e696c0a
0x8048538 :  0x0a0a3465      0x656e696c

<= YOU'LL NOTICE THE "0x0a" CHARACTERS IN THE EXPECTED PLACES...

Just a thought .. PSM

Biotachyonic · 08-25-2005, 03:01 PM

Looks like it worked perfectly. Not understand what your problem is. I'm sure you know that when you printf s it is going to print on the same line until there is a \n(newline), then it's going to go down a row, and go on printing till the next \n.

exvor · 08-26-2005, 01:55 PM

Yea im a little confused on exactly what your problem is here too. Looks like the computer did exactly
what you told it to do.

???

sirclif · 08-26-2005, 03:16 PM

i think his problem is that he es expecting his output to look like:

line1
line2
(line 3 is blank)
line4
line5
line6

but he's getting it all spit out onto two lines.

is that right?

what do you get if you do:

printf("Now the buffer is \n");
printf(buffer);

boxerboy · 08-26-2005, 04:25 PM

shouldnt he need a " afer each \n??? i thought in C you had to have many " if all on one line in source code?

Code:

$1 = "line1\nline2 (line 3 is blank\nline4\n\nline5\n\nline6\000\000"