Two Russian girls were dead set on going to NYC for a very suspicious job offer. A worried friend of theirs posted a question, the rest you can read for yourself.

Here is a simple example, note that each has a specific value to ensure that each matches a single bit in the 8-bit variable:

enum options {
  option_a = 0x01,  /*   1 == 00000001 */
  option_b = 0x02,  /*   2 == 00000010 */
  option_c = 0x04,  /*   4 == 00000100 */
  option_d = 0x08,  /*   8 == 00001000 */
  option_e = 0x10,  /*  16 == 00010000 */
  option_f = 0x20,  /*  32 == 00100000 */
  option_g = 0x40,  /*  64 == 01000000 */
  option_h = 0x80,  /* 128 == 10000000 */
};

So basically we have 8 boolean flags (0 off/false, 1 on/true). We can use these by utilising bitwise operations. There is really only 3 operations that you will use regularly on bit flags so lets see them.

Switching individual/multiple options “on” (or setting value true):

options |= option_a;
/* Translates to:
  options = options | option_a;
  options = 00000000 | 00000001;
  options = 00000001;
*/
 
options = option_a | option_c | option_h;
/* Translates to:
  options = 00000001 | 00000100 | 10000000;
  options = 10000101;
*/

Equally switching options “off” (or setting false) can be done as follows (note we are using the options from above, thus a, c and h are on):

options &= ~option_a;
/* Translates to:
  options = options & ~option_a;
  options = 10000101 & ~00000001;
  options = 10000101 & 11111110;
  options = 10000100;
*/

Obviously you need a basic grasp of boolean mathematics to be able to handle this but learning the basics shouldn’t be too hard. Finally the last thing to do is check to see if a flag is “on” or “off” (again using the options from before, so c and h are “on”:

if( options & option_b ) printf("B is ON\n");
/* 10000100 & 00000010 = 00000000 .. i.e. false, so no output */
if( options & option_c ) printf("C is ON\n");
/* 10000100 & 00000100 = 00000100 .. i.e. true, so "C is ON" is outputting */

As with most things in C, once you start using and abusing it should start to fall into place. I hope that this serves as a basic introduction to bit fields.

Let’s see how we’d do that:

#include <stdarg.h>
#include <stdio.h>
 
int Adding(int cnt, ...) {  /* the three ... indicate a variable list */
    int add, tmp, i;
    va_list args;            /* make a va_list */
    va_start(args, cnt);     /* variable list starts after 'cnt' */
    for(i = 0; i < cnt; i++) {
        tmp = va_arg(args, int); /* grab the next */
        add = add + tmp;         /* add to the sum */
    }
    va_end(args);    /* finished using variable list */
    return add;
}
 
int main( ) {
    int a;
    a = Adding(2, 1, 2);
    printf("%u\n", a);     /* Outputs 3 */
    a = Adding(3, 1, 2, 3);
    printf("%u\n", a);     /* Outputs 6 */
    return 0;
}

So the first argument indicates how many variables we are going to pass and the rest are summed together. The function Adding() would be identical in C++.

[root@marine]# ls
adobe-release-i386-1.0-1.noarch.rpm
[root@marine]# yum localinstall adobe-release-i386-1.0-1.noarch.rpm
Loaded plugins: fastestmirror, priorities
Setting up Local Package Process
Examining adobe-release-i386-1.0-1.noarch.rpm: adobe-release-i386-1.0-1.noarch
Marking adobe-release-i386-1.0-1.noarch.rpm to be installed
Loading mirror speeds from cached hostfile
* addons: anorien.csc.warwick.ac.uk
* base: anorien.csc.warwick.ac.uk
* centosplus: anorien.csc.warwick.ac.uk
* contrib: anorien.csc.warwick.ac.uk
* extras: anorien.csc.warwick.ac.uk
* rpmforge: fr2.rpmfind.net
* updates: anorien.csc.warwick.ac.uk
588 packages excluded due to repository priority protections
Resolving Dependencies
--> Running transaction check
---> Package adobe-release-i386.noarch 0:1.0-1 set to be updated
--> Finished Dependency Resolution

Dependencies Resolved

================================================================================
Package              Arch     Version Repository                          Size
================================================================================
Installing:
adobe-release-i386   noarch   1.0-1   /adobe-release-i386-1.0-1.noarch   1.9 k

Transaction Summary
================================================================================
Install      1 Package(s)
Update       0 Package(s)
Remove       0 Package(s)

Total size: 1.9 k
Is this ok [y/N]: y
Downloading Packages:
warning: rpmts_HdrFromFdno: Header V3 DSA signature: NOKEY, key ID f6777c67

Public key for adobe-release-i386-1.0-1.noarch.rpm is not installed

As you can see it attempted to install but because the key was missing it refused to install. So what do we do to find that key? First we must download the key from somewhere, there is various key servers around the world, some of the most popular are (note hkp is the HTTP keyserver protocol):

• hkp://subkeys.pgp.net
• hkp://pgp.mit.edu
• hkp://keys.gnupg.net
• hkp://wwwkeys.uk.pgp.net (where UK can be replaced by any country code)

So lets search for the missing key:

[root@marine]# gpg --keyserver hkp://wwwkeys.uk.pgp.net --recv-keys f6777c67
gpg: requesting key F6777C67 from hkp server wwwkeys.uk.pgp.net
gpg: /root/.gnupg/trustdb.gpg: trustdb created
gpg: key F6777C67: public key "Adobe Systems Incorporated (Linux RPM
  Signing Key) " imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg:               imported: 1

So now we have the key and see that it is indeed Adobe’s key. Now all we need to do is add into RPM:

[root@marine]# gpg --armor --export f6777c67 >tmp-gpg.key
[root@marine]# rpm --import tmp-gpg.key

Simple as that, the install will work now!

This post is a refreshed look at a previous post on the same matter.

I have also added a Google CSE to assist with searching for a particular post, although I don’t exactly have too many.

I am very impressed with how WordPress has improved over recent times. The automatic upgrade is impressive and will surely ensure that less WP installs are hacked. The theme/plug-in search is quick and very easy to use, thus insuring that people will not be stuck with one design, or missing a vital plug-in. These two can be upgraded on the fly. Overall a real improvement proving that WP is a mature and stable piece of software.

There is only one minor annoyance and that is the speed at which pages are served, I do feel it could be slightly quicker.

Hope you all enjoy the updates that I applied!

Strange what goes through the brain of MS Business Productivity.

Polish Alternative

English Alternative

I highly suggest that you give it a go first on your own and see how far you get. I was completely stumped on some of the stuff and others quickly sliced through them.

Have a go at the Funny Farm puzzle.

For those of you that enjoy spoilers, here is the completed puzzle:
Completed Funny Farm

ENOTOBACCO		Read on an empty pipe
EBEFOREI		Invalid syntax
ECHERNOBYL		Core dumped
ECRAY			Program exited before being run
EDINGDONG		The daemon is dead
EFLAT			System needs tuning
EGEEK			Program written by inept Frat member
EIEIO			Here-a-bug, there-a-bug, ....
EIUD			Missing period
ELECTROLUX		Your code could stand to be cleaned up
EMILYPOST		Wrong fork
END.ARMS.CONTROL	Silo overflow
ENOHORSE		Mount failed
ENONSEQUETOR		C program not derived from main(){printf("Hello, world");}
EWATERGATE		Extended tape gap
EWOK			Aliens sighted
EWOK			Your code appears to have been stir-fried
EWOULDBNICE     	The feature you want has not been implemented yet

Not to be out done, a new signal:

SIGNUKE     	Nuclear event occurred (cannot be caught or ignored)

As always looking through info and man pages can provide a raft of information about tools and sometimes uncover tricks that you might of otherwise not known about!

This is the new minimalistic theme, Wonderful! Good job Google.