Binary Tides

Mysql Database stores dates in the format :
yyyy-mm-dd e.g. 2009-04-15

Whereas humans are more used to the formats like :
dd-mm-yyyy or mm-dd-yyyy e.g. 21-04-2009

And while reading a format like :
dd-Month-yyyy is more usable e.g. 21-Mar-2009

Checking a valid date :
If the date is in format dd-mm-yyyy then a simple way to test its validity would be :

if(strtotime(implode('-', array_reverse(explode('-', $date)))))
    return true;

But the above has an issue that it will report 31-02-2009 as a valid date. The same with strptime.

Another function checkdate is useful for this issue and it also manages leap years.

$datearr = explode('-', $date);
list($d,$m,$y) = $datearr;
if(checkdate($m, $d, $y))
    return true;

But a small issue with checkdate is that it reports a date like 01-01-2500 to be valid again (which is , as per what checkdate is supposed to do).

Using strptime to check a date being in a valid dd-mm-yyyy format :

/*
    Check date to be in format dd-mm-yyyy
*/
function valid_date($date) {
    #Check format
    if(!strptime($date , '%d-%m-%Y'))
 return false;

    $parts = explode('-' , $date);
    $d = $parts[0];
    $m = $parts[1];
    $y = $parts[2];
    #Check format of year number
    if(!($y >= 1000 && $y <= 9999))
 return false;
    return true;
}

or more simply :

if(strtotime(implode('-', array_reverse(explode('-', $date)))))
    return true;
else
    return false;

Using strptime to convert a date in dd-mm-yyyy format to yyyy-mm-dd the code could be :

/*
    Convert a dd-mm-yyyy into yyyy-mm-dd for mysql insertion
*/
function dbdate($date) {
    $d = strptime($date , '%d-%m-%Y'); #This is the user input format
    if($d)
        $date = ($d['tm_year']+1900).'-'.($d['tm_mon']+1).'-'.$d['tm_mday'];
    else
        $date = '1800-01-01';
    return $date;
}

or more simply :

if(strtotime(implode('-', array_reverse(explode('-', $date)))))
    return implode('-', array_reverse(explode('-', $date)));
else
    return '1800-01-01';

The above function would convert a date in the format dd-mm-yyyy to yyyy-mm-dd.
e.g. $date = dbdate($date) where $date = “02-04-2006″
now $date is ready to be inserted in the mysql database

Checking date format and range :

function valid_date($date , $range=0) {

    $datearr = explode('-', $date);
    if(count($datearr) != 3)
 return false;
    list($d, $m, $y) = $datearr;
    #Check validity
    if($range == 1) {
 #Check date format with range and validity
 if(checkdate($m , $d , $y) and strtotime("$y-$m-$d")) #strtotime to invalidate outrange dates like 01-01-2500
     return true;
    }
    else {
 #Check date format and validity and not range
 if(checkdate($m , $d , $y)) #strtotime to invalidate outrange dates like 01-01-2500
     return true;
    }
    return false;
}

The above function can just check the date format or the range as well depending on the value of the $range parameter. checkdate() invalidates dates like 31-02-2009 and takes care of leap years as well. Whereas strotime checks the range of the date. The above function checks the format dd-mm-yyyy and dd-mm-yy. A little modification would adapt it to formats dd-mm-yyyy , dd-mm-yy dd/mm/yyyy and dd/mm/yy :

/*
 Checks the date validity in formats :
 1. dd-mm-yyyy
 2. dd-mm-yy
 3. dd/mm/yyyy
 4. dd/mm/yy

*/
function valid_date($date , $range=0) {
 #For valid dd/mm/yyyy
 $date = str_replace('/', '-', $date);
 #Check
 $datearr = explode('-', $date);
 if(count($datearr) != 3)
  return false;
 list($d, $m, $y) = $datearr;
 #Check validity
 if($range == 1) {
  #Check date format with range and validity
  if(checkdate($m , $d , $y) and strtotime("$y-$m-$d")) #strtotime to invalidate outrange dates like 01-01-2500
   return true;
 }
 else {
  #Check date format and validity and not range
  if(checkdate($m , $d , $y)) #strtotime to invalidate outrange dates like 01-01-2500
   return true;
 }
 return false;
}

/*
    Give a dd-month-yyyy representation of mysql format yyyy-mm-dd
*/
function showdate($dbdate) {
    $stamp = strtotime($dbdate);
    if($stamp)
        return strftime("%d-%b-%Y",$stamp); #This is the user viewing format
    else
        return '';
}

While printing dates in a table for viewing purpose a format like 02-Mar-2010 is easily readable and the above function does the same. It converts 2010-03-02 to 02-Mar-2010.

/*
    Convert yyyy-mm-dd to dd-mm-yyyy
*/
function feeddate($dbdate) {
    $stamp = strtotime($dbdate);
    if($stamp)
        return strftime("%d-%m-%Y",$stamp); #This is the user viewing format
    else
        return '';
}

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