Bitwise Operators

guybrun

Hi,

I am having trouble using the bitwise operator NOT (~). I have the following code:

$var = 29;
#convert the decimal to a binary string
$var = decbin( $var );
#the echo command gives the following output
11101
#Invert the binary string
$var = ~$var;
echo $var;
#the echo command gives the following output
ÎÎÎÏÎ

So I end up with just garbage. Does anyone have any good suggestions?

Thanks,
-Guy

AstroTeg

When you echo $var for the 2nd time (reflecting the not operation you did), you need to use decbin like you did the first time.

Sgarissta

Originally posted by AstroTeg
When you echo $var for the 2nd time (reflecting the not operation you did), you need to use decbin like you did the first time.

Actually your problem is that you've taken $var=decbin($var);

So when you do ~$var you're 'notting' the STRING value of $var. So still sticking with the one var method replace
$var=~$var
with
$var = decbin(~(bindec($var)));

AstroTeg

Sgarissta - I've tested with his code and a simple decbin just needs to be added. Oddly enough, it works and PHP makes the transition from string to decimal ok (although I don't know if I would trust it).

A simplier approach might to keep everything as decimal until you need to do output:

$var = 29;
echo decbin($var) . '<br>';
$var = ~$var;
echo decbin($var) . '<br>';

Sgarissta

Originally posted by AstroTeg
Sgarissta - I've tested with his code and a simple decbin just needs to be added. Oddly enough, it works and PHP makes the transition from string to decimal ok (although I don't know if I would trust it).

A simplier approach might to keep everything as decimal until you need to do output:

(feels like an idiot)

I wrote that reply off the hip, just did some testing locally, and you are correct, it did the string->dec conversion correctly.

I've played quite a bit with the bitwise stuff, and i learned pretty quickly to explicitly store the numbers NOT as strings, much easier to go bug hunting anyway. 🙂

guybrun

Thanks a lot everyone. I have tested the code and it works nice. :-)