#39579 [Bgs]: Comparing zero & string values in boolean comparison has unexpected behaviour

ID: 39579 User updated by: iain at workingsoftware dot com dot au Reported By: iain at workingsoftware dot com dot au Status: Bogus Bug Type: Variables related Operating System: FreeBSD 6.1 PHP Version: 5.2.0 New Comment: it's not the behaviour of how a string is cast to an integer that i'm talking about, but if i have a comparison: if($value == Class::CONSTANT) and the class constant is a string, it's not immediately apparent that if $value == 0 then this will evaluate to true. maybe warning is too strong, but a notice might be good in the event that a non-strict == operation returns true because one of the operands is 0 and the other operand is a value that evaluates to 0 when cast as an int. anyway, i guess if php has been around for this long without anyone mentioning it yet ... i mean, this is the first time i've come across the problem. if a notice had been emitted it would have been a time saver. Previous Comments: ------------------------------------------------------------------------ [2006-11-22 11:06:57] mgf@php.net And, besides, this behaviour is documented at http://www.php.net/manual/en/language.types.string.php#language.types.string.conversion ------------------------------------------------------------------------ [2006-11-22 09:39:26] johannes@php.net Thank you for taking the time to write to us, but this is not a bug. Please double-check the documentation available at http://www.php.net/manual/ and the instructions on how to report a bug at http://bugs.php.net/how-to-report.php That's how PHP works and it won't change. ------------------------------------------------------------------------ [2006-11-22 08:35:22] iain at workingsoftware dot com dot au well it seems to me that at least a warning should be given when comparing an integer 0 to a non-integer value that evaluates to 0 when cast as an int unless an explicit type cast is used without using strict equals. i can see why this behaviour is not a bug, because (int)'SOME STRING' == 0, but it's also has the potential to cause unexpected results/bugs unless you use strict equals everywhere. in this case, i fixed the problem by using === instead of ==, but it took a bit of time to track down the error because there was no warning or anything. i think that it would be better to require someone to do: if($value == (int)'SOME STRING') OR if($value === 'SOME STRING') in order to avoid a warning being emmited if $value == 0. ------------------------------------------------------------------------ [2006-11-22 08:17:01] derick@php.net Thank you for taking the time to write to us, but this is not a bug. Please double-check the documentation available at http://www.php.net/manual/ and the instructions on how to report a bug at http://bugs.php.net/how-to-report.php . ------------------------------------------------------------------------ [2006-11-22 07:31:34] iain at workingsoftware dot com dot au Description: ------------ if you have a variable with the value 0 assigned to it and do a comparison with a non-integer then the non-integer value is cast to an int with unexpected results. it behaves differently when comparing a non-zero integer. Reproduce code: --------------- put this in test.php and run php -f test.php: <?php $zero = 0; $one = 1; if($zero == 'SOME STRING') echo("0 does equal 'SOME STRING'\n"); else echo("0 does not equal 'SOME STRING'\n"); if($one == 'SOME STRING') echo("1 does equal 'SOME STRING'\n"); else echo("1 does not equal 'SOME STRING'\n"); ?> Expected result: ---------------- 0 does not equal 'SOME STRING' 1 does not equal 'SOME STRING' Actual result: -------------- 0 does equal 'SOME STRING' 1 does not equal 'SOME STRING' ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=39579&edit=1