Re: Watch out for automatic type casting

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On 29 Mar 2012, at 17:57, Arno Kuhl wrote:

> I found automatic typecasting can be a bit of a gotcha.
> 
> 
> 
> $sText = "this.is.a.test.text";
> 
> if ( $pos = strpos($sText, "test") !== FALSE) {
> 
>                echo  substr($sText, 0, $pos)."<".substr($sText, $pos,
> strlen("test")).">".substr($sText, $pos+strlen("test"));
> 
> }
> 
> 
> 
> The code seems logical enough, and the expected result would be:
> 
> this.is.a.<test>.text
> 
> 
> 
> In fact it ends up being:
> 
> t<his.>is.a.test.text
> 
> 
> 
> The reason is $pos is typecast as TRUE, not int 10, presumably because it's
> in the same scope as the boolean test.
> 
> Then when $pos is later used as an int it's converted from TRUE to 1.
> 
> 
> 
> You have to bracket the $pos setting to move it into its own scope to
> prevent it being typecast:
> 
> if ( ($pos = strpos($sText, "test")) !== FALSE) {
> 
> 
> 
> No doubt it's mentioned somewhere in the php manual, I just never came
> across it.
> 
> Just thought I'd highlight one of the gotchas of auto typecasting for any
> other simpletons like me.

This is not due to typecasting, it's due to operator precedence.

In PHP (and many other languages) the !== comparison operator will get done first, so the result of that comparison will be assigned to $pos. By introducing the brackets you're explicitly specifying the order.

Details here: http://php.net/operators.precedence

-Stuart

-- 
Stuart Dallas
3ft9 Ltd
http://3ft9.com/
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