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Re: switch with case 0 [message #182590 is a reply to message #182589]

Sat, 17 August 2013 06:35

J.O. Aho
Messages: 194
Registered: September 2010

Karma:

Senior Member

On 17/08/13 06:55, Fiver wrote:
> This example
>
> switch ("foo") {
> case 0:
> echo "'foo' is 0\n";
> break;
> default:
> echo "'foo' is not 0\n";
> }
>
> will print: 'foo' is 0.

The switch you are doing is equal to a

if("foo" == 0) {}

PHP will make a type casting and try to make the "foo" to a integer, as
it's not a string only of numeric characters and those it will be cast
to a 0 which makes your statement true.

You can try this one:

switch("123") {
case 0:
echo "it's 0\n";
break;

case 123:
echo "it's 123\n";
break;

default:
echo "it's NOT 0 nor 123\n";
}

> I know how to avoid the problem, I'm just wondering what kind of
> comparison is used that makes "foo" equal to 0? The manual mentions
> "loose comparison", but this is even looser than usual.

No it's not looser than normally, PHP don't care so much about data
types so it internally casts it just to make it easy for those who ain't
so good at programming.

> By the way, the original code was meant to validate SORT_* arguments.
> It's a little harder to spot here:
>
> switch ($mode) {
> case SORT_ASC:
> case SORT_DESC:
> case SORT_REGULAR:
> case SORT_NUMERIC:
> case SORT_STRING:
> case SORT_LOCALE_STRING:
> case SORT_NATURAL:
> case SORT_FLAG_CASE:
> break;
> default:
> throw new \InvalidArgumentException("invalid sort mode: $mode");
> }
>
> SORT_REGULAR is 0, so if the input is a string, this will break (literally).

Sounds like you are trusting user input, always validate the user input
to be a valid value of the type you are requiring. In this case
is_numeric() could save you from trouble.

--

//Aho

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[Message index]

		switch with case 0 By: Fiver on Sat, 17 August 2013 04:55
		Re: switch with case 0 By: J.O. Aho on Sat, 17 August 2013 06:35
		Re: switch with case 0 By: The Natural Philosoph on Sat, 17 August 2013 07:29
		Re: switch with case 0 By: Luuk on Sat, 17 August 2013 07:51
		Re: switch with case 0 By: Thomas Mlynarczyk on Sat, 17 August 2013 11:16
		Re: switch with case 0 By: Peter H. Coffin on Sat, 17 August 2013 15:56
		Re: switch with case 0 By: The Natural Philosoph on Sat, 17 August 2013 16:45
		Re: switch with case 0 By: Tim Streater on Sat, 17 August 2013 17:58
		Re: switch with case 0 By: The Natural Philosoph on Sat, 17 August 2013 18:39
		Re: switch with case 0 By: Thomas Mlynarczyk on Sat, 17 August 2013 19:36
		Re: switch with case 0 By: Thomas Mlynarczyk on Sat, 17 August 2013 20:14
		Re: switch with case 0 By: Norman Peelman on Sat, 17 August 2013 17:56
		Re: switch with case 0 By: Thomas Mlynarczyk on Sat, 17 August 2013 19:55
		Re: switch with case 0 By: The Natural Philosoph on Sat, 17 August 2013 20:04
		Re: switch with case 0 By: Thomas Mlynarczyk on Sat, 17 August 2013 20:32
		Re: switch with case 0 By: Richard Yates on Sat, 17 August 2013 22:20
		Re: switch with case 0 By: Fiver on Sat, 17 August 2013 20:37
		Re: switch with case 0 By: Norman Peelman on Sat, 17 August 2013 23:26
		Re: switch with case 0 By: The Natural Philosoph on Sun, 18 August 2013 11:54
		Re: switch with case 0 By: Norman Peelman on Sun, 18 August 2013 00:23
		Re: switch with case 0 By: Thomas Mlynarczyk on Sun, 18 August 2013 13:22
		Re: switch with case 0 By: Norman Peelman on Sun, 18 August 2013 15:20
		Re: switch with case 0 By: Thomas Mlynarczyk on Sun, 18 August 2013 16:28
		Re: switch with case 0 By: Norman Peelman on Sun, 18 August 2013 19:16
		Re: switch with case 0 By: Norman Peelman on Sun, 18 August 2013 22:04
		Re: switch with case 0 By: Thomas Mlynarczyk on Sun, 18 August 2013 22:17
		Re: switch with case 0 By: Thomas Mlynarczyk on Sun, 18 August 2013 22:13
		Re: switch with case 0 By: The Natural Philosoph on Sun, 18 August 2013 23:35
		Re: switch with case 0 By: Norman Peelman on Mon, 19 August 2013 10:30
		Re: switch with case 0 By: Norman Peelman on Mon, 19 August 2013 02:13
		Re: switch with case 0 By: Thomas Mlynarczyk on Mon, 19 August 2013 17:55
		Re: switch with case 0 By: Thomas 'PointedEars' on Mon, 19 August 2013 08:18
		Re: switch with case 0 By: Thomas Mlynarczyk on Mon, 19 August 2013 17:39
		Re: switch with case 0 By: Fiver on Sat, 17 August 2013 14:15
		Re: switch with case 0 By: Norman Peelman on Sat, 17 August 2013 17:28

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