Question

I have dates in the following format (yyyymmdd, 18751104, 19140722)... what's the easiest way to convert it to date().... or is using mktime() and substrings my best option...?

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Solution

Use strtotime() to convert a string containing a date into a Unix timestamp:

<?php
// both lines output 813470400
echo strtotime("19951012"), "\n",
     strtotime("12 October 1995");
?>

You can pass the result as the second parameter to date() to reformat the date yourself:

<?php
// prints 1995 Oct 12
echo date("Y M d", strtotime("19951012"));
?>

Note

strtotime() will fail with dates before the Unix epoch at the start of 1970.

As an alternative which will work with dates before 1970:

<?php
// Returns the year as an offset since 1900, negative for years before
$parts = strptime("18951012", "%Y%m%d");
$year = $parts['tm_year'] + 1900; // 1895
$day = $parts['tm_mday']; // 12
$month = $parts['tm_mon']; // 10
?>

OTHER TIPS

Personally, I'd just use substr() because it's probably the lightest way to do it anyway.

But here's a function that takes a date, of which you can specify the format. It returns an associative array, so you could do for example (untested):

$parsed_date = date_parse_from_format('Ymd', $date);
$timestamp = mktime($parsed_date['year'], $parsed_date['month'], $parsed_date['day']);

http://uk.php.net/manual/en/function.date-parse-from-format.php

Although I must say, I don't find that any easier or more effective than simply:

mktime(substr($date, 0, 4), substr($date, 4, 2), substr($date, 6, 2));

have a look at strptime

Well thanks for all the answers but the 1900 problem seems to plague every response I got. Here is a copy of the function I am using should someone find it useful for them in the future.

public static function nice_date($d){
    $ms = array(
           'January',
           'February',
           'March',
           'April',
           'May',
           'June',
           'July',
           'August',
           'September',
           'October',
           'November',
           'December'
    );

    $the_return = '';
    $the_month = abs(substr($d,4,2));
    if ($the_month != 0) {
        $the_return .= $ms[$the_month-1];
    }

    $the_day = abs(substr($d,6,2));
    if ($the_day != 0){
        $the_return .= ' '.$the_day;
    }

    $the_year = substr($d,0,4);
    if ($the_year != 0){
        if ($the_return != '') {
            $the_return .= ', ';
        }
        $the_return .= $the_year;
    }

    return $the_return;
}

(PHP 5 >= 5.3.0, PHP 7):

You can get a DateTime instance with:

$dateTime = \DateTime::createFromFormat('Ymd|', '18951012');

and convert it to a timestamp:

$timestamp = $dateTime->getTimestamp();
// -> -2342217600
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