[PHP] Re: strcmp() versus ==
Clancy wrote:
> On Mon, 16 Mar 2009 17:06:35 -0500, nos...@mckenzies.net (Shawn McKenzie)
> wrote:
>
>> Shawn McKenzie wrote:
>>> Paul M Foster wrote:
I had never completely read over the rules with regard to comparisons in
PHP, and was recently alarmed to find that $str1 == $str2 might not
compare the way I thought they would. Is it common practice among PHP
coders to use strcmp() instead of == in making string comparisons? Or am
I missing/misreading something?
Paul
>>> I would use $str1 === $str2 if you want to make sure they are both
>>> strings and both the same value.
>>>
>>> Since PHP is loosely typed, "0" == 0 is true however "0" === 0 is false.
>>>
>> If you want to force a string comparison you can also use:
>>
>> (string)$str1 == (string)$str2
>
> Recently there was some discussion about inexplicable results from sorting
> alphanumeric
> strings. Inspired by your suggestion I filled in an array with random 4
> character
> alphanumeric strings, and then wrote a simple bubblesort. I made two copies
> of the array,
> and sorted one using a simple comparison, and the other using the above
> comparison. The
> initial values of the array were :
>
> $aa = array
> ('ASDF','01A3','0A13',1,'00A3','','001A','','7205','00Z0');
>
> (There are no letter 'O's in this),
>
> And the results I got were:
>
> Tb2_38: Original Raw comp String Comp
> ASDF
> 01A300A3 001A
> 0A1301A3 00A3
> 1 0A13 00Z0
> 00A3ASDF 01A3
> 0A13
> 001A1 1
> 001A 7205
> 720500Z0 ASDF
> 00Z07205
>
> Apart from the out of place '1', apparently treated as '1000', which I threw
> in out of
> curiosity, the string comparison gave the expected results, but I cannot see
> the logic of
> the raw comparison. Can anybody explain these results?
>
> Clancy
>
> If anyone is suspicious the actual code I used was:
>
>
> $aa = array
> ('ASDF','01A3','0A13',1,'00A3','','001A','','7205','00Z0');
>
> $k = count ($aa); $bb = $aa; $cc = $aa;
> while ($k > 1)
> {
> $i = 0; $j = 1; while ($j < $k)
> {
> if ($cc[$i] > $cc[$j])
> {
> $t = $cc[$i]; $cc[$i] = $cc[$j]; $cc[$j] = $t;
> }
> ++$i; ++$j;
> }
> --$k;
> }
>
> $k = count ($aa);
> while ($k > 1)
> {
> $i = 0; $j = 1; while ($j < $k)
> {
> if ((string)$bb[$i] > (string)$bb[$j])
> {
> $t = $bb[$i]; $bb[$i] = $bb[$j]; $bb[$j] = $t;
> }
> ++$i; ++$j;
> }
> --$k;
> }
>
> echo 'Tb2_38: Original Raw comp String
> Comp';
> $i = 0; $k = count ($aa);
> while ($i < $k)
> {
> echo '
> '.$aa[$i].
> ''.$cc[$i].
>
> ' '.$bb[$i].'';
> ++$i;
> }
Just a quick look, your original post was about comparing "strings" and
as far as I know, unless you force a string comparison the < and > will
do a numerical comparison, and even if I'm wrong, anything compared to
your 1 will be a numerical comparison. If your just trying to sort,
check out sort() and natsort().
--
Thanks!
-Shawn
http://www.spidean.com
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[PHP] Re: strcmp() versus ==
On Mon, 16 Mar 2009 17:06:35 -0500, nos...@mckenzies.net (Shawn McKenzie) wrote:
>Shawn McKenzie wrote:
>> Paul M Foster wrote:
>>> I had never completely read over the rules with regard to comparisons in
>>> PHP, and was recently alarmed to find that $str1 == $str2 might not
>>> compare the way I thought they would. Is it common practice among PHP
>>> coders to use strcmp() instead of == in making string comparisons? Or am
>>> I missing/misreading something?
>>>
>>> Paul
>>>
>>
>> I would use $str1 === $str2 if you want to make sure they are both
>> strings and both the same value.
>>
>> Since PHP is loosely typed, "0" == 0 is true however "0" === 0 is false.
>>
>
>If you want to force a string comparison you can also use:
>
>(string)$str1 == (string)$str2
Recently there was some discussion about inexplicable results from sorting
alphanumeric
strings. Inspired by your suggestion I filled in an array with random 4
character
alphanumeric strings, and then wrote a simple bubblesort. I made two copies of
the array,
and sorted one using a simple comparison, and the other using the above
comparison. The
initial values of the array were :
$aa = array
('ASDF','01A3','0A13',1,'00A3','','001A','','7205','00Z0');
(There are no letter 'O's in this),
And the results I got were:
Tb2_38: Original Raw comp String Comp
ASDF
01A300A3 001A
0A1301A3 00A3
1 0A13 00Z0
00A3ASDF 01A3
0A13
001A1 1
001A 7205
720500Z0 ASDF
00Z07205
Apart from the out of place '1', apparently treated as '1000', which I threw in
out of
curiosity, the string comparison gave the expected results, but I cannot see
the logic of
the raw comparison. Can anybody explain these results?
Clancy
If anyone is suspicious the actual code I used was:
$aa = array
('ASDF','01A3','0A13',1,'00A3','','001A','','7205','00Z0');
$k = count ($aa); $bb = $aa; $cc = $aa;
while ($k > 1)
{
$i = 0; $j = 1; while ($j < $k)
{
if ($cc[$i] > $cc[$j])
{
$t = $cc[$i]; $cc[$i] = $cc[$j]; $cc[$j] = $t;
}
++$i; ++$j;
}
--$k;
}
$k = count ($aa);
while ($k > 1)
{
$i = 0; $j = 1; while ($j < $k)
{
if ((string)$bb[$i] > (string)$bb[$j])
{
$t = $bb[$i]; $bb[$i] = $bb[$j]; $bb[$j] = $t;
}
++$i; ++$j;
}
--$k;
}
echo 'Tb2_38: Original Raw comp String
Comp';
$i = 0; $k = count ($aa);
while ($i < $k)
{
echo '
'.$aa[$i].
''.$cc[$i].
' '.$bb[$i].'';
++$i;
}
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Re: [PHP] Re: strcmp() versus ==
On Tue, 2009-03-17 at 08:09 +0200, Alpár Török wrote: > 2009/3/17 Shawn McKenzie : > > Shawn McKenzie wrote: > >> Paul M Foster wrote: > >>> I had never completely read over the rules with regard to comparisons in > >>> PHP, and was recently alarmed to find that $str1 == $str2 might not > >>> compare the way I thought they would. Is it common practice among PHP > >>> coders to use strcmp() instead of == in making string comparisons? Or am > >>> I missing/misreading something? > >>> > >>> Paul > >>> > >> > >> I would use $str1 === $str2 if you want to make sure they are both > >> strings and both the same value. > >> > >> Since PHP is loosely typed, "0" == 0 is true however "0" === 0 is false. > >> > > > > If you want to force a string comparison you can also use: > > > > (string)$str1 == (string)$str2 > > > > -- > > Thanks! > > -Shawn > > http://www.spidean.com > > > > -- > > PHP General Mailing List (http://www.php.net/) > > To unsubscribe, visit: http://www.php.net/unsub.php > > > > > AFAIK strcmp and strncmp are faster. At least for the second i > remember seeing benchmarks that proved that. Then you must have seen a bad benchmark. strncmp() has specific purposes and so does strcmp() where you would choose it instead of == or ===. But with respect to speed, if all you want to know is whether two strings are the same then == or === will be faster since they are operators and do not have the same overhead as a function call. Cheers, Rob. -- http://www.interjinn.com Application and Templating Framework for PHP -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] Re: strcmp() versus ==
2009/3/17 Shawn McKenzie : > Shawn McKenzie wrote: >> Paul M Foster wrote: >>> I had never completely read over the rules with regard to comparisons in >>> PHP, and was recently alarmed to find that $str1 == $str2 might not >>> compare the way I thought they would. Is it common practice among PHP >>> coders to use strcmp() instead of == in making string comparisons? Or am >>> I missing/misreading something? >>> >>> Paul >>> >> >> I would use $str1 === $str2 if you want to make sure they are both >> strings and both the same value. >> >> Since PHP is loosely typed, "0" == 0 is true however "0" === 0 is false. >> > > If you want to force a string comparison you can also use: > > (string)$str1 == (string)$str2 > > -- > Thanks! > -Shawn > http://www.spidean.com > > -- > PHP General Mailing List (http://www.php.net/) > To unsubscribe, visit: http://www.php.net/unsub.php > > AFAIK strcmp and strncmp are faster. At least for the second i remember seeing benchmarks that proved that. -- Alpar Torok -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
[PHP] Re: strcmp() versus ==
Shawn McKenzie wrote: > Paul M Foster wrote: >> I had never completely read over the rules with regard to comparisons in >> PHP, and was recently alarmed to find that $str1 == $str2 might not >> compare the way I thought they would. Is it common practice among PHP >> coders to use strcmp() instead of == in making string comparisons? Or am >> I missing/misreading something? >> >> Paul >> > > I would use $str1 === $str2 if you want to make sure they are both > strings and both the same value. > > Since PHP is loosely typed, "0" == 0 is true however "0" === 0 is false. > If you want to force a string comparison you can also use: (string)$str1 == (string)$str2 -- Thanks! -Shawn http://www.spidean.com -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
[PHP] Re: strcmp() versus ==
Paul M Foster wrote: > I had never completely read over the rules with regard to comparisons in > PHP, and was recently alarmed to find that $str1 == $str2 might not > compare the way I thought they would. Is it common practice among PHP > coders to use strcmp() instead of == in making string comparisons? Or am > I missing/misreading something? > > Paul > I would use $str1 === $str2 if you want to make sure they are both strings and both the same value. Since PHP is loosely typed, "0" == 0 is true however "0" === 0 is false. -- Thanks! -Shawn http://www.spidean.com -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
