Clancy schreef: > While PHP has a lot of nice features, it also has some traps which I am forever falling > into. One which I find particularly hard to understand is how mixed mode comparisons work. > For instance > > $string = 'elephant'; > If($string == 0) returns true; > If($string != 0) returns false; > If($string === 0) returns false; > > I know that in this case I should use 'If($string == '')', but I still manage to forget. > Can anyone explain clearly why comparing a string with zero gives this apparently > anomalous result? it's called auto-casting (or auto-typecasting) and it's 'by design' ... welcome to the world of dynamic typing. try this to see it working: php -r ' var_dump((integer)"elephant"); var_dump((float)"elephant"); var_dump((bool)"elephant"); var_dump((array)"elephant"); var_dump((object)"elephant"); var_dump((bool)(integer)"elephant"); ' you can avoid auto-casting if needed, in a variety of ways: php -r ' $foo = "elephant"; if (!empty($foo)) echo "$foo found!\n"; if (strlen($foo)) echo "$foo found!\n"; if (is_string($foo) && strlen($foo)) echo "$foo found!\n"; if ($foo !== "") echo "$foo found!\n"; if ($foo === "elephant") echo "$foo found!\n"; ' those last 2 show how to use 'type-checked' equality testing. > -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
