php.net |  support |  documentation |  report a bug |  advanced search |  search howto |  statistics |  random bug |  login

go to bug id or search bugs for

Bug #28515 A simple comparision operation FAILS!
Submitted: 2004-05-25 06:20 UTC Modified: 2004-05-25 11:18 UTC
From: andrew dot panin at nvkz dot net Assigned:
Status: Not a bug Package: Output Control
PHP Version: Irrelevant OS: Windows 98 SE
Private report: No CVE-ID: None
View Add Comment Developer Edit
Welcome back! If you're the original bug submitter, here's where you can edit the bug or add additional notes.
If this is not your bug, you can add a comment by following this link.
If this is your bug, but you forgot your password, you can retrieve your password here.
Password:
Status:
Package:
Bug Type:
Summary:
From: andrew dot panin at nvkz dot net
New email:
PHP Version: OS:

 

 [2004-05-25 06:20 UTC] andrew dot panin at nvkz dot net 
Description:
------------
Just look into the code!

Reproduce code:
---------------
<?php
 $in="1234567";
 $d = 0;
 $d = 3*abs(strlen($in)/3 - floor(strlen($in)/3));

  print $d;
//here $d=1, as it PHP print

 if ($d == 1) { print "E"; }
//The "E" is NOT prints!

 die();
?>

Expected result:
----------------
That the "E" will be shown.

Actual result:
--------------
NOTHING!!!

Patches

Add a Patch

Pull Requests

Add a Pull Request

History

AllCommentsChangesGit/SVN commitsRelated reports
 [2004-05-25 11:18 UTC] helly@php.net 
Floating point values have a limited precision. Hence a value might 
not have the same string representation after any processing. That also
includes writing a floating point value in your script and directly 
printing it without any mathematical operations.
 
Thank you for your interest in PHP.

Look at this:
marcus@frodo php-cvs $ php -r \'var_dump(3*(7/3 - 2) == 1);\'
bool(false)

(7/3-2) == 1/3 but a float can never be 1/3 exact.
E.g. floats cannot handle fractions.
 [2004-05-25 11:18 UTC] lars_stegelitz at col dot wunderman dot com 
This happens on 4.3.7dev too, but...

It seems to be a representation problem of 'print $d;'.
If you modify your if-clause the following way, it shows what I mean:

if ($d > 1) { print "E"; }

Now, the 'E' is printed ! It seems, that the value of $d is NOT exactly one :

if (((int)$d) == 1) { print "E"; }

Whent $d is converted to integer, the 'E' is printed also. 
Use number_format($d, 20); to see an internal value representation of $d (it reads 1.00000000000000044409). 

When working with floating point values, never ever test on equality!
 
PHP Copyright © 2001-2024 The PHP Group
All rights reserved. 		Last updated: Fri Apr 19 08:01:28 2024 UTC