gregoriantojd

Converts a Gregorian date to Julian Day Count

&reftitle.description; `int` `gregoriantojd` `int` `month` `int` `day` `int` `year`

The valid range for the Gregorian calendar is from November 25, 4714 B.C. to at least December 31, 9999 A.D.

Although this function can handle dates all the way back to 4714 B.C., such use may not be meaningful. The Gregorian calendar was not instituted until October 15, 1582 (or October 5, 1582 in the Julian calendar). Some countries did not accept it until much later. For example, Britain converted in 1752, The USSR in 1918 and Greece in 1923. Most European countries used the Julian calendar prior to the Gregorian.

&reftitle.parameters;

`month`

- The month as a number from 1 (for January) to 12 (for December)

`day`

- The day as a number from 1 to 31. If the month has less days then given, overflow occurs; see the example below.

`year`

- The year as a number between -4714 and 9999. Negative numbers mean years B.C., positive numbers mean years A.D. Note that there is no year `0`; December 31, 1 B.C. is immediately followed by January 1, 1 A.D.

&reftitle.returnvalues;

The julian day for the given gregorian date as an integer. Dates outside the valid range return `0`.

&reftitle.examples;

### Calendar functions

    <?php
    $jd = gregoriantojd(10, 11, 1970);
    echo "$jd\n";
    $gregorian = jdtogregorian($jd);
    echo "$gregorian\n";
    ?>

&example.outputs;

    2440871
    10/11/1970

### Overflow behavior

    <?php
    echo gregoriantojd(2, 31, 2018), PHP_EOL,
         gregoriantojd(3,  3, 2018), PHP_EOL;
    ?>

&example.outputs;

    2458181
    2458181

&reftitle.seealso;

- `jdtogregorian`
- `cal_to_jd`