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Date: Mon, 15 Aug 2011 06:28:49 +0200
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Subject: Re: [PHP-DEV] [VOTE]strn(case)cmp supporting a negative length as
 its third paramter
From: sebastian.krebs.berlin@googlemail.com (Sebastian Krebs)



Am 14.08.2011 23:52, schrieb Rasmus Lerdorf:
> On 08/14/2011 02:37 PM, Rasmus Lerdorf wrote:
>> On 08/14/2011 02:03 PM, Stas Malyshev wrote:
>>> Hi!
>>>
>>> On 8/14/11 11:40 AM, Rasmus Lerdorf wrote:
>>>> My main issue with changing strncmp/strncasecmp is that these are
>>>> currently exact mappings of the underlying libc functions. For people
>>>
>>> And why should anybody care? 99% of people using PHP never used a libc
>>> function and can hardly tell libc from gcc. If we can extend this
>>> function with useful functionality, nobody cares about what libc does.
>>>
>>>> For example, I could imagine people writing code along these lines:
>>>>
>>>> $len = strlen($user_data) - strlen($suffix);
>>>> if(!strncmp($user_data, $string, $len)) {
>>>>      // do something
>>>> }
>>>
>>> Warning doesn't fix the bug - and unless you're in 0.0001% of the
>>> population that actually reads the logs daily and checks every message
>>> there it would be little to help you. We should have more useful
>>> functions, not more warnings. Warning won't make this code to work.
>>
>> I agree, however this change would potentially change the return value
>> of the function. Before it would warn and not match. Even if you never
>> saw the warning, at least length -1 would not give you a match. Now if
>> the user data happens to end with the right character we now have a
>> string match which is not at all what the code was written to do.
>
> Put more succinctly. Subtle BC breaks like this worry me. Any strncmp()
> call with a computed length where that length may in some cases go
> negative will now potentially return a match where it wouldn't before.
> This would be very hard to track down. And the reason for introducing
> this subtle BC break is so that you can rewrite:
>
>     if (substr("prefix_num", -3) == "num") {
>          echo "they have same suffix\n";
>     }
>
>
> into:
>
>     if (strncmp("prefix_num", "num", -3) === 0) {
>          echo "they have same suffix\n";
>     }
>
> That doesn't seem like a big win to me.

Or just

     if (strncmp(strrev('prefix_num'), 'mun', 3) === 0) {
         // do something
     }


>
> -Rasmus
>


Regards,
Sebastian