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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.php
Subject: Re: Check for military time
Date: Thu, 22 Oct 2015 15:11:42 +0200
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Stephan Elinghaus wrote:

> Am 2015-10-20 hat Derek Turner geschrieben:
>> Is there a quick and dirty way to check that
>>
>> substr($string, 0 ,3) is a valid military time, ie. 0000-2359?
> 
> Maybe this works for you:
> <?php
> $string="1534";
> if(preg_match("/[012](((?<=2)[0123])|(?<!2)[0-9])[[0-5][0-9]/",$string))

Much too complicated, and still not completely safe (you have not anchored 
the expression, neither on beginning or end of string or line, whitespace 
nor non-digits).  Consider instead:

  if (preg_match('/^(?:[01]\\d|2[0-3])[0-5]\\d$/', $string))

Test code:

$ php -r 'foreach (range(-1, 24) as $h) foreach (range(-1, 60) as $m) { echo 
preg_match("/^(?:[01]\\d|2[0-3])[0-5]\\d$/", sprintf("%02d", $h) . 
sprintf("%02d", $m)); if ($m === 60) echo "\n"; }'

You should get a box of zeros filled only with ones (because '0' is the 
string representation of “false”, and '1' of “true”).  The zeros are (quite 
literally) the edge cases that must not match, the ones the proper time 
strings.

> echo "is valid";
> else echo "is not valid";

With all such constructs, consider instead:

  echo ($boolean) ? $ifTrue : $ifFalse;

This is particularly useful if you can use “<?= … ?>” to just output the 
(string representation of) the result of an expression.

> ?>

Avoid ending PHP files with that; you may be accidentally outputting 
trailing whitespace otherwise.

-- 
PointedEars
Zend Certified PHP Engineer
Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.