[SOLVED] bitrwise operator..

[DanDaBeginner]

I dont really understand the purpose of bitwise operator... (such as : ^,|,~<<,>>)

 

when can it be useful and what do they do? I tried reading some tutorial and the php manual..but Im really confuse..please somebody adjust the screw on my brain...it seems to be loosing...

 

thanks

[Orio]

I personally never had the need to use them when programming in php, but I guess they can be used for encoding/decoding stuff, and in other mathematical stuff.

When I used assembly I used them alot.

 

Orio.

[tibberous]

Bitwise operator is really only used for encryption and for bitsets, which let you put a bunch of binary settings in a single variable.

 

You can also use the bit operator as an or that doesn't short, same for and.

[DanDaBeginner]

thank you tibberous,

 

thank you Orio, even if the need of bitwise is not that much.. i really want to grab the concept behind it.. explaing it to me will be helpful...

 

bitsets? binary setting in a single variable? what is that? sorry for my ignorance but I really like to know this one...

[tibberous]

Some languages short ors and ands, not sure if php does.

 

It works like this:

 

Lets say you have an if statement:

 

if($word1 == 'true' && $word2 == 'false')

 

Now, if $word1 is not equal to 'true', the if is false, regardless of $word2. Rather than calculate the irrelevant $word2 == 'false', it just skips it and evaluates the if to false. In this case it doesn't matter, but if the line was something like:

 

if($word1 == 'true' && ($words--)>0)

 

then shorting the if would keep $words-- from happening if $word1 was not equal to 'true'. Makes for a bitch of a runtime error, and using ^ in place of && keeps it from happening....

 

I think...

 

Might just be C++...

 

or Java...

 

Try it

 

Also, I don't think there is any guarantee the conditions are evaluated in order, and it might be there evaluated in reverse.

[zq29]

http://www.phpfreaks.com/forums/index.php/topic,113143.msg459615.html#msg459615

[HuggieBear]

Very useful for security permissions.

 

Regards

Huggie

[tibberous]

My research has found that php does short expressions, that ^ and | keeps it from doing that, and that it seems to go from left to right, but that might not be guaranteed.

 

And ^ ands bits, which is like adding them, except it doesn't carry. So...

 

1010 ^

1100 =

0110

 

You kind of have to know a little bit about binary, it's hard to explain online.

 

It isn't used much. You only have to use it if it's built into a 3rd party library, and even then you don't really have to understand it.

[ToonMariner]

I use them for permissions - its exactly the same system used for your dir/file permissions on a server

 

http://www.phpfreaks.com/tutorials/151/0.php

[DanDaBeginner]

thanks guys...