datetime-php-examples-arithmetic-4

  • Examples

    • DateTime Arithmetic

  • DateTime Arithmetic

    • DateTime Arithmetic

    DateTime Arithmetic

    The following examples show some pitfalls of
    DateTime arithmetic with regard to DST transitions and months
    having different numbers of days.

    Example #1 DateTime::add/sub add intervals which cover
    elapsed time

    Adding PT24H over a DST transition will appear to add 23/25
    hours (for most timezones).

    <?php
    $dt     = new DateTime("2015-11-01 00:00:00", new DateTimeZone("America/New_York"));
    echo     "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
    $dt->add(new DateInterval("PT3H"));
    echo     "End:   ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
    ?>

    The above example will output:

    Start: 2015-11-01 00:00:00 -04:00
End:   2015-11-01 02:00:00 -05:00

    Example #2 DateTime::modify and strtotime increment or
    decrement individual component values

    Adding +24 hours over a DST transition will add exactly 24 hours
    as seen in the date/time string (unless the start or end time is on
    a transition point).

    <?php
    $dt     = new DateTime("2015-11-01 00:00:00", new DateTimeZone("America/New_York"));
    echo     "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
    $dt->modify("+24 hours");
    echo     "End:   ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
    ?>

    The above example will output:

    Start: 2015-11-01 00:00:00 -04:00
End:   2015-11-02 00:00:00 -05:00

    Example #3 Adding or subtracting times can over- or
    underflow dates

    Like where January 31st + 1 month will result in March 2nd (leap
    year) or 3rd (normal year).

    <?php
    echo "Normal year:\n"; // February has 28 days
    $dt = new DateTime("2015-01-31 00:00:00", new DateTimeZone("America/New_York"));
    echo     "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
    $dt->modify("+1 month");
    echo     "End:   ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;

    echo "Leap year:\n"; // February has 29 days
    $dt = new DateTime("2016-01-31 00:00:00", new DateTimeZone("America/New_York"));
    echo     "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
    $dt->modify("+1 month");
    echo     "End:   ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
    ?>

    The above example will output:

    Normal year:
Start: 2015-01-31 00:00:00 -05:00
End:   2015-03-03 00:00:00 -05:00
Leap year:
Start: 2016-01-31 00:00:00 -05:00
End:   2016-03-02 00:00:00 -05:00

    To get the last day of the next month (i.e. to prevent the
    overflow), the last day of format is available as of PHP
    5.3.0.

    <?php
    echo "Normal year:\n"; // February has 28 days
    $dt = new DateTime("2015-01-31 00:00:00", new DateTimeZone("America/New_York"));
    echo     "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
    $dt->modify("last day of next month");
    echo     "End:   ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;

    echo "Leap year:\n"; // February has 29 days
    $dt = new DateTime("2016-01-31 00:00:00", new DateTimeZone("America/New_York"));
    echo     "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
    $dt->modify("last day of next month");
    echo     "End:   ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
    ?>

    The above example will output:

    Normal year:
Start: 2015-01-31 00:00:00 -05:00
End:   2015-02-28 00:00:00 -05:00
Leap year:
Start: 2016-01-31 00:00:00 -05:00
End:   2016-02-29 00:00:00 -05:00