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Bug #12566 Cascaded ternaries evaluate incorrectly
Submitted: 2001-08-04 15:33 UTC Modified: 2001-10-13 13:41 UTC
From: nick at macaw dot demon dot co dot uk Assigned:
Status: Not a bug Package: *Programming Data Structures
PHP Version: 4.0.6 OS: Linux
Private report: No CVE-ID: None
View Developer Edit
 [2001-08-04 15:33 UTC] nick at macaw dot demon dot co dot uk 
The following emits 'two' rather than 'one' as one would expect.

$a = 1; $b = 2;

echo (($a == 1) ? 'one' : 
      ($b == 2) ? 'two' :
      'unknown');

Apologies if for PHP this unusual behaviour actually is as expected, but being counter-intuituve, and of course inconsistent from other languages with a ?: operator, this is an undesirable result.

In 'C', the following of course outputs 'one'

#include <stdio.h>

int main()
{
  int a = 1, b = 2;

  puts((a == 1) ? "one" : 
       (b == 2) ? "two" :
       "unknown");

  return 0;
}

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 [2001-08-04 17:04 UTC] jeroen@php.net 
Confirmed in latest CVS:

---
echo TRUE ? 'one' : TRUE ? 'two' : 'unknown';
=> two
---
echo TRUE ? 'one' : FALSE ? 'two' : 'unknown';
=> two
---
This definitely is a bug, and IMO a serious one. A parse error would be acceptable IMO (then use ( and )), but this isn't.
 [2001-08-04 17:21 UTC] jeroen@php.net 
adam@trachtenberg.com:
> It's not a "bug," but a "feature." :)
> 
> PHP has the inverse associativity of ?: compared to C (and every other
> language). This was originally a mistake, but now "it won't be changed,"
> due to historical reasons.
> 
> See some messages I had on php-dev back around the first week of January,
> 2001 on this topic. FWIW, I would like to change it.
> 
> -adam

So, you need to read it as:

echo (TRUE ? 'one' : TRUE) ? 'two' : 'unknown';,
and 
echo 'one' ? 'two' : 'unknown' is, correctly, 'two'


Maybe a fix for PHP 4.1 / PHP 5?
 [2001-10-13 13:41 UTC] sterling@php.net 
nope.
 
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