[VOTE]strn(case)cmp supporting a negative length as its third paramter View as Markdown

Hi,

Doesn't substr_compare() accomplish the same thing since 5.1.0?

The only thing I couldn't figure out is how to make it case
insensitive without specifying an explicit value to $length

Best,
Tjerk

Hi:
  compare to use substr,   strncmp supporting negative lenght can
save a temp variable.

thanks

2011/8/15 Rasmus Lerdorf rasmus@php.net:

Hi!

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.

-Rasmus

--

--
Laruence  Xinchen Hui
http://www.laruence.com/

--

--

Tjerk

Hi:

I think we are not talking about how to accomplish a function, we
are talking about how to do it better

and, in fact, I think strrev is need more cpu time and alloc space,
although they are very tiny :)

thanks

2011/8/15 Sebastian Krebs sebastian.krebs.berlin@googlemail.com:

Am 14.08.2011 23:52, schrieb Rasmus Lerdorf:

Hi!

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

--

--
Laruence  Xinchen Hui
http://www.laruence.com/