What arguments are required?

I have the following code and when I call <?php compare_update ?> I get a PHP error that tells me I'm missing argument 1. Looking at the code can someone tell me what the variable for argument 1 is supposed to be?

function compare_update( $post_id ) {
    //Assign Posts to Variables
    $start = $_POST['_date_start'];
    $end = $_POST['_date_end'];

    //Parse Start Date
    if($start):
        $start = explode('-', $start);
        $start = mktime($hour, $_POST['_date_minute'], 0, $start[0], $start[1], $start[2]);
        $compare = date('ymd', $start);
    endif;

    //Parse End Date
    if($end):
        $today = date('ymd');
        $end = explode('-', $end);
        $end = mktime($hour, $_POST['_date_minute'], 0, $end[0], $end[1], $end[2]);

        // If today's date is within the date range of an event that spans multiple days & the event is NOT YET PAST
        if ((date('ymd',$start) < date('ymd',$end)) && (date('ymd',$end) >= $today) ){
            // and the start date is before today
            if (date('ymd',$start) < $today){
                $compare = date('ymd'); //Overwrite start date $compare
            } else {
                $compare = date('ymd', $start);
            }
        } else {
            $compare = date('ymd', $start);         
        }
    endif;      

    //Check if values exist and then update
    if($end):
        update_post_meta( $post_id, '_date_end', $end);
    el开发者_C百科se:
        if($start)update_post_meta( $post_id, '_date_end', $start);
    endif;
    if($start)update_post_meta( $post_id, '_date_start', $start);
    if($compare)update_post_meta( $post_id, '_date_compare', $compare);

    if($echo): echo $compare; else: return $compare; endif;
}

Your function says:

function compare_update( $post_id ) {

Yet you don't call it with any argument, like:

compare_update('100'); // Or some number/id/whatnot,
                       // more than likely a $_POST['id']
                       // or $_GET['id'] variable

When you create a function in PHP with arguments, and you don't give a default value within the argument list, you have to provide a corresponding variable within the function call for each argument that requires an input.

// $post_id is an argument
function compare_update( $post_id ) { 
    ... your code ...
}

So now you've created a function that requires one parameter be passed in the function call, which then is usable by that label within the function.

$post_id = $_POST['id'];
compare_update($post_id); // This is passing a parameter

For instance, you're using it down towards the end of the function:

//Check if values exist and then update
if($end):
    update_post_meta( $post_id, '_date_end', $end);
else:
    if($start)update_post_meta( $post_id, '_date_end', $start);
endif;
if($start)update_post_meta( $post_id, '_date_start', $start);
if($compare)update_post_meta( $post_id, '_date_compare', $compare);

if($echo): echo $compare; else: return $compare; endif;

Also, your code formatting is confusing. For instance, the code directly above could be:

//Check if values exist and then update
if ($end) {
    update_post_meta( $post_id, '_date_end', $end);
} else {
    if ($start) {
        update_post_meta( $post_id, '_date_end', $start);
    }
}
if ($start) {
    update_post_meta( $post_id, '_date_start', $start);
}
if ($compare) {
    update_post_meta( $post_id, '_date_compare', $compare);
}
if ($echo) {
    echo $compare;
} else {
    return $compare;
}

The parameter to compare_update()?

You need to pass it the $post_id.

Are you sending compare_update a parameter? Like this:

compare_update($someNumber);

Looks like it's supposed to be the post id?

In other words,

<?php compare_update($id); ?>

where $id was set to the post_id you wish to compare_update to.