Re: [PHP] How can an elephant count for nothing?

Thu, 12 Feb 2009 08:10:23 -0800

Jochem Maas wrote: 
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.
because  intval("elephant") == 0;
intval will convert the string into integer , Strings will most likely return 0 although this depends on the leftmost characters of the string.

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