Bug #73940 [Opn->Nab]: the associativity is uncertain for complex ++/-- operation
| From: | requinix@php.net | Date: | Sun, 15 Jan 2017 05:39:37 +0000 |
| Subject: | Bug #73940 [Opn->Nab]: the associativity is uncertain for complex ++/-- operation | ||
| References: | 1 | Groups: | php.bugs |
| Request: | Send a blank email to php-bugs+get-206627@lists.php.net to get a copy of this message | ||
Edit report at https://bugs.php.net/bug.php?id=73940&edit=1
ID: 73940
Updated by: requinix@php.net
Reported by: hu60 dot cn at gmail dot com
Summary: the associativity is uncertain for complex ++/--
operation
-Status: Open
+Status: Not a bug
Type: Bug
Package: Scripting Engine problem
Operating System: Windows & Linux
PHP Version: 7.1.0
Block user comment: N
Private report: N
New Comment:
As in other languages, the order of execution is undefined.
http://php.net/manual/en/language.operators.precedence.php
> Operator precedence and associativity only determine how expressions are
> grouped, they do not specify an order of evaluation. PHP does not (in the
> general case) specify in which order an expression is evaluated and code that
> assumes a specific order of evaluation should be avoided, because the behavior
> can change between versions of PHP or depending on the surrounding code.
Previous Comments:
------------------------------------------------------------------------
[2017-01-15 05:31:41] hu60 dot cn at gmail dot com
Description:
------------
$x = 8;
$y = ++$x;
$z = $x + --$x + $x;
var_dump($x, $y, $z);
// output: int(8) int(9) int(24)
$x = 8;
$y = ++$x;
$z = ($a = $x) + --$x + $x;
var_dump($x, $y, $z, $a);
// output: int(8) int(9) int(25) int(9)
It's so amazing!
Should $x + --$x + $x be equal 24 or 25?
Test script:
---------------
<?php
$x = 8;
$y = ++$x;
$z = $x + --$x + $x;
var_dump($x, $y, $z);
echo '<hr>';
$x = 8;
$y = ++$x;
$z = ($c = (($a = $x) + ($b = --$x))) + ($d = $x);
var_dump($x, $y, $z, $a, $b, $c, $d);
echo '<hr>';
$x = 8;
$y = ++$x;
$z = (($x) + (--$x)) + ($x);
var_dump($x, $y, $z);
echo '<hr>';
$x = 8;
$y = ++$x;
$z = ($a = $x) + --$x + $x;
var_dump($x, $y, $z, $a);
?>
Expected result:
----------------
int(8) int(9) int(25)
int(8) int(9) int(25) int(9) int(8) int(17) int(8)
int(8) int(9) int(25)
int(8) int(9) int(25) int(9)
Actual result:
--------------
int(8) int(9) int(24)
int(8) int(9) int(25) int(9) int(8) int(17) int(8)
int(8) int(9) int(24)
int(8) int(9) int(25) int(9)
------------------------------------------------------------------------
--
Edit this bug report at https://bugs.php.net/bug.php?id=73940&edit=1