note 80672 deleted from language.types.string by danbrown

Note Submitter: topnotcher at mail dot uri dot edu ---- @qriz at example dot com Numerical comparisons, such as <, > are simply _NOT_ valid on strings. Thus, before a comparison can be made by a numerical comparison operator, the operands must be _casted_ to a numerical type (either float or int). What I was attempting to say in my previous post is that >, < are date-aware; the tests I included were examples, and not intended to represent the full scope of my comparison. "Works correctly since there is a comparing between strings. The comparisson is done on the last number/letter (since thats the only thing that is difference in the string) and that is in this case: the 9 and 8." What you say here is mere assumption; a few quick tests show that this is indeed not the case. If PHP indeed compares only the last character in the string, then the following assertion should be false: test.php: <?php $a = '2007-11-06 15:17:48'; $b = '2007-11-05 15:17:48'; var_dump($a > $b); ?> mArIo@luigi ~ $: php test.php bool(true) Further, consider the following choices for $a and $b, which, as expected, demonstrate that the <, > operators can indeed understand date formats: <?php $a = 'January 25th, 2008 00:23:37'; $b = 'January 24th, 2008 00:23:38'; // ($a > $b) === true, but 8 ?> If you remain unconvinced, consider what happens if I spell January incorrectly: <?php $a = 'January 25th, 2008 00:23:38'; $b = 'Janury 24th, 2008 00:23:37'; // ($a > $b) === false ?> Looks like it can understand ISO 8601 date formats? (for more information, see http://en.wikipedia.org/wiki/ISO_8601) Further investigation yields that this doesn't even work as it should: <?php $a = 'February 1st, 2008 00:23:38'; $b = 'January 25th, 2008 00:23:38'; var_dump($a > $b); //bool(false) var_dump(strtotime($a)); //int(1201843418) var_dump(strtotime($b)); //int(1201238618) var_dump(strtotime($a) - strtotime($b)); //int(604800) ?> Keeping $b constant and varying the month in $a shows that this comparison correctly interprets the date with the following months: January,March,May,June,July,September,October,November. Interestingly enough, these are all the months having the property that ord($a[0]) >= ord($b[0]). <?php var_dump('Z' > 'M'); //bool(true) ?> Conclusion: The <,> comparison operators definitely have functionality that is undocumented, including date awareness; however, this functionality may not always work as expected and should not be trusted for portability.