#20673 [Ver->Bgs]: Inexplicable arithmetical error due to references

ID: 20673 Updated by: andi@php.net Reported By: dakota@dir.bg -Status: Verified +Status: Bogus Bug Type: Scripting Engine problem Operating System: Win 2000 NT/Linux PHP Version: 4.3.0-dev/4.4.0-dev New Comment: Like in most other programming languages you can't use post/pre increment operators on a variable which is used more than once in an expression. The result is undefined. We won't print out a warning (like most other languages). If you want the result to be 16 then do the following: $a = 7; $b =& $a; $a++; $a = $a + $a; echo $a; //the result is 15; ?> Previous Comments: ------------------------------------------------------------------------ [2002-11-30 09:28:17] dakota@dir.bg O.K. but it's PHP - not C. And, if it's wrong, why the parser don't warn me? ------------------------------------------------------------------------ [2002-11-29 13:11:42] sesser@php.net never write something like $a = $a + $a++; if you f.e. try such a construct in C you will get different results depending on the compiler and/or optimisation level. ------------------------------------------------------------------------ [2002-11-27 07:04:52] dakota@dir.bg <? $a = 7; $a = $a + $a++; echo $a; //the result is 14; ?> When I add a reference to $a, the behavior of $a + $a++ becomes inexplicable different. Note that $a isn't changed anywhere! <? $a = 7; $b =& $a; $a = $a + $a++; echo $a; //the result is 15; ?> The only difference is $b =& $a, but why $a takes care of references to itself? ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=20673&edit=1