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Full Discussion: A trivial XOR doubt in a program
Top Forums Programming A trivial XOR doubt in a program Post 302247279 by royalibrahim on Wednesday 15th of October 2008 10:09:49 AM
Old 10-15-2008
A trivial XOR doubt in a program
Hi,

I am trying to reverse a string using the following program utilizing the Exclusive OR bit operation:

Code:
int main() {
   char str[] = "Quraish";
   char *p = str, temp;
   char *q = str + strlen(str) - 1;
   while ( p != q ) {
      if (*p != *q) {
         *p ^= *q; *q ^= *p; *p ^= *q;
      }
      p++; q--;
   }
   printf("%s \n", str);
}

The above code works perfectly alright, but if I change the line
Code:
*p ^= *q; *q ^= *p; *p ^= *q;

to
Code:
*p ^= *q ^= *p ^= *q;

(I am trying to do swapping inline)
it prints an empty string. Could anyone tell me why this behaviour is?
 

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LEARN ABOUT DEBIAN

empty-page

EMPTY-PAGE(1)							 ExactImage Manual						     EMPTY-PAGE(1)

NAME

       empty-page - empty page detector of the ExactImage toolkit

SYNOPSIS

       empty-page [option...] {-i | --input} input-file

       empty-page {-h | --help}

DESCRIPTION

       ExactImage is a fast C++ image processing library. Unlike many other library frameworks it allows operation in several color spaces and bit
       depths natively, resulting in low memory and computational requirements.

       empty-page counts dark pixels of a black and white image and decides with a threshold whether the page is most probably empty, and thus can
       be removed from the image processing stream.

OPTIONS

       -i file, --input file
	   Read image from the specified file.

       -m n, --margin n
	   Set width of border margin to skip. For speed reasons, the margin has to be a multiple of 8. The default is 16.

       -p x, --percentage x
	   Set fraction of permissible dark pixels. The default is 0.05 (5%).

       -h, --help
	   Display help text and exit.

EXAMPLES

	   $ empty-page -i test.tif
	   The image has 75461 dark pixels from a total of 1060992 (7.11231%).
	   non-empty

EXIT STATUS

       The exit status is 0 if the image is mostly white, 1 otherwise.

SEE ALSO

       exactimage(7)

AUTHORS

       Jakub Wilk <jwilk@debian.org>
	   Wrote this manual page for the Debian system.

       http://www.exactcode.de/site/open_source/exactimage/
	   This manual page incorporates texts found on the ExactImage homepage.

COPYRIGHT

       This manual page was written for the Debian system (and may be used by others).

       Permission is granted to copy, distribute and/or modify this document under the terms of the GNU General Public License, Version 2 or (at
       your option) any later version published by the Free Software Foundation.

       On Debian systems, the complete text of the GNU General Public License can be found in /usr/share/common-licenses/GPL-2.

empty-page							    09/09/2013							     EMPTY-PAGE(1)
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