Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people, just like you, are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
Solved

!! operator

Posted on 2003-11-17
5
326 Views
Last Modified: 2012-05-04
edit - - i get it
0
Comment
Question by:jini555
  • 3
  • 2
5 Comments
 
LVL 19

Expert Comment

by:Dexstar
ID: 9766495
jini555:

> int i = !! (SHORT) j;

! = Boolean NOT
!! = Boolean NOT NOT

It's silly, but that's what it means.  You should avoid using it.  It is the same as saying this:
   int i = (j != 0);

Hope That Helps,
Dex*
0
 
LVL 45

Accepted Solution

by:
Kent Olsen earned 50 total points
ID: 9766534


Depending on the compiler, optimization, and the mood of the guy implementing this, the two "!" operators may cancel each other out.

But in real life, they don't.  The first "!" operator (actually, the righter-most of the two) implicitly converts (short)j to a boolean value so that the result will be 0 or 1.  The second "!" operator then complements the value so that the net effect is the same as:

  int i = ((short)j) ? 1 : 0;



Kent
0
 
LVL 45

Expert Comment

by:Kent Olsen
ID: 9766540

Isn't it amazing how many "other ways" there are to do things in C?

:)

0
 
LVL 19

Expert Comment

by:Dexstar
ID: 9766594
Kent:

Yeah it is.  These two are equivilant:
     int i = ((short)j) ? 1 : 0;

And:
     int i = (j != 0);

Dex*
0
 
LVL 45

Expert Comment

by:Kent Olsen
ID: 9766631

Actually, they're not.

if *j* is a variable type that is longer than a short, then your test MAY fail depending on the value of *j*.  You need to recast it as a short (to truncate the upper bits) before testing its value.

But with that small change, we do have three ways to do the same thing that I'd do in two lines of assembler.  :)

Kent
0

Featured Post

Back Up Your Microsoft Windows Server®

Back up all your Microsoft Windows Server – on-premises, in remote locations, in private and hybrid clouds. Your entire Windows Server will be backed up in one easy step with patented, block-level disk imaging. We achieve RTOs (recovery time objectives) as low as 15 seconds.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Have you thought about creating an iPhone application (app), but didn't even know where to get started? Here's how: ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Important pre-programming comments: I’ve never tri…
An Outlet in Cocoa is a persistent reference to a GUI control; it connects a property (a variable) to a control.  For example, it is common to create an Outlet for the text field GUI control and change the text that appears in this field via that Ou…
The goal of this video is to provide viewers with basic examples to understand and use structures in the C programming language.
The goal of this video is to provide viewers with basic examples to understand how to create, access, and change arrays in the C programming language.

809 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question