usort() Behavior?

[Alan Little]

I wrote a sorting function to use with usort(). It worked fine, and I
went on with the development of my code. At one point I changed the name
of the sorting function, but forgot to update it in the usort() call.
Yet, it still was working. I removed the usort() call to make sure my
data didn't just happen to be arriving in sorted order, and it wasn't.

When I removed the usort() call, the code broke; when I put it back, it
worked. I changed the name of the callback function in the usort() call
to random letters, and it still worked. How is this possible? Does usort
"remember" the last valid sorting algorithm it had? To test this wild
hypothesis, I uploaded the code to a server where it had never run. It
still works. WTH?

The elements of the array I'm sorting are each an array with two
elements, and I'm sorting on the second element, in reverse order. Is
this the default behavior for usort() if it can't find the callback
function? This is really bizarre. Anyone know what's going on?

--
Alan Little
Phorm PHP Form Processor
http://www.phorm.com/

[Pedro Graca]

Alan Little wrote:
[edited]

I wrote a sorting function to use with usort(). [...] changed the name
of the sorting function, but forgot to update it in the usort() call.
Yet, it still was working. [...] I changed the name of the callback function in the usort() call
to random letters, and it still worked.

Post the part of your code that calls usort(), the callback comparison
function.
Additionally, insert

error_reporting(E_ALL);
ini_set('display_errors', '1');

at the top of your code.
--
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== ** ## !! !! ## ** ==
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[Alan Little]

Carved in mystic runes upon the very living rock, the last words of Pedro
Graca of comp.lang.php make plain:

Alan Little wrote:
[edited]

I wrote a sorting function to use with usort().

[...]

changed the name
of the sorting function, but forgot to update it in the usort() call.
Yet, it still was working.

[...]

I changed the name of the callback function in the usort() call
to random letters, and it still worked.

Post the part of your code that calls usort(), the callback comparison
function.

Additionally, insert

error_reporting(E_ALL);
ini_set('display_errors', '1');

at the top of your code.

OK, I completely isolated the code, set up some test data, and tried it
again. Here's the sorting function:

function TestSort($a, $b) {
if ($a[1] == $b[1]) return 0;
return ($a[1] > $b[1]) ? -1 : 1;
}

Here's some sample data:

$Data = array (
array ('Some Data 1', 56),
array ('Some Data 2', 78),
array ('Some Data 3', 25),
array ('Some Data 4', 43)
);

Calling usort() with 'TestSort' gives the expected results. Calling it
with 'xxx' gives me a reversed array:

0
0 -> Some Data 4
1 -> 43
1
0 -> Some Data 3
1 -> 25
2
0 -> Some Data 2
1 -> 78
3
0 -> Some Data 1
1 -> 56

Apparently *this* is the default behavior. My live data contained only
two elements, which happened to be in ascending order, thus appeared that
it was actually sorting them. Mystery solv-ed.

Interestingly, it doesn't give so much as a Notice.

--
Alan Little
Phorm PHP Form Processor
http://www.phorm.com/

[Alan Little]

Carved in mystic runes upon the very living rock, the last words of Alan
Little of comp.lang.php make plain:

Calling usort() with 'TestSort' gives the expected results. Calling it
with 'xxx' gives me a reversed array:

Apparently *this* is the default behavior. My live data contained only
two elements, which happened to be in ascending order

Doh! Here's a lesson boys and girls: KISS (Keep It Simple, Stupid).

The data didn't "happen" to be in ascending order. I re-examined my code
and realized it would *always* be in ascending order, thus all I have to
do is call array_reverse().

Oh well. Hey, even experienced programmers can waste an hour chasing
their tail.

--
Alan Little
Phorm PHP Form Processor
http://www.phorm.com/

[Pedro Graca]

Alan Little wrote:

Interestingly, it doesn't give so much as a Notice.

php$ cat alan.php
<?php
error_reporting(E_ALL);
ini_set('display_errors', '1');

function TestSort($a, $b) {
if ($a[1] == $b[1]) return 0;
return ($a[1] > $b[1]) ? -1 : 1;
}

/* Here's some sample data: */

$Data = array (
array ('Some Data 1', 56),
array ('Some Data 2', 78),
array ('Some Data 3', 25),
array ('Some Data 4', 43)
);

/* test 1 */
$Data1 = $Data;
usort($Data1, 'TestSort');
print_r($Data1);
echo "\n\n========\n\n";

/* test 2 */
$Data2 = $Data;
usort($Data2, 'xxx');
print_r($Data2);
echo "\n\n========\n\n";

?>

php$ php alan.php
Array
(
[0] => Array
(
[0] => Some Data 2
[1] => 78
)

[1] => Array
(
[0] => Some Data 1
[1] => 56
)

[2] => Array
(
[0] => Some Data 4
[1] => 43
)

[3] => Array
(
[0] => Some Data 3
[1] => 25
)

)
========
Warning: usort(): Invalid comparison function. in
/home/pedro/src/php/alan.php on line 21
Array
(
[0] => Array
(
[0] => Some Data 1
[1] => 56
)

[1] => Array
(
[0] => Some Data 2
[1] => 78
)

[2] => Array
(
[0] => Some Data 3
[1] => 25
)

[3] => Array
(
[0] => Some Data 4
[1] => 43
)

)
========
php$

--
Mail sent to my "From:" address is publicly readable at http://www.dodgeit.com/
== ** ## !! !! ## ** ==
TEXT-ONLY mail to the complete "Reply-To:" address ("My Name" <my@address>) may
bypass the spam filter. I will answer all pertinent mails from a valid address.

[Alan Little]

Carved in mystic runes upon the very living rock, the last words of Pedro
Graca of comp.lang.php make plain:

Alan Little wrote:

Interestingly, it doesn't give so much as a Notice.

Warning: usort(): Invalid comparison function. in
/home/pedro/src/php/alan.php on line 21

Interesting. I even threw in an undefined variable to make sure the error
reporting was set properly. It gave me a Notice, but nothing from usort().
Maybe a platform (Win) or version (4.3.6) issue. Oh well, no big deal.

--
Alan Little
Phorm PHP Form Processor
http://www.phorm.com/