PHP - determine whether the variable is undefined or NULL

There is a much more elegant way since PHP 7 called Null coalescing operator:

$variable1 = $_POST['ABC'] ?? 'DEFAULT VALUE'

If you just want to set defaults:

PHP < v7 (ternary)

$var = isset($_POST['ABC'])) ? $_POST['ABC'] : false;

PHP >= v7 (null coalesce)

$var = $_POST['ABC'] ?? false;

Any (roughly equivalent)

$var = false;

if(isset($_POST['ABC'])) $var = $_POST['ABC'];

If $_POST['ABC'] does not exist, then PHP will raise an error at exactly this point:

init_variable($_POST['ABC'])

You cannot prevent this error from happening from within init_variable. Your function will only receive the end result of trying to access an undefined variable/index, it cannot prevent that from happening.

What you want is simply the null coalescing operator:

$variable1 = $_POST['ABC'] ?? '123';

Or perhaps:

$variable2 = isset($_POST['ABC']) ? $_POST['ABC'] : '123';

You could include this in your project

https://github.com/rappasoft/laravel-helpers/blob/master/src/helpers.php

or use this variety

if ( ! function_exists('array_get'))
{
    /**
     * Get an item from an array using "dot" notation.
     *
     * @param  array   $array
     * @param  string  $key
     * @param  mixed   $default
     * @return mixed
     */
    function array_get($array, $key, $default = null)
    {
        if (is_null($key)) return $array;
        if (isset($array[$key])) return $array[$key];
        foreach (explode('.', $key) as $segment)
        {
            if ( ! is_array($array) || ! array_key_exists($segment, $array))
            {
                return $default;
            }
            $array = $array[$segment];
        }
        return $array;
    }
}

What it does is split the string by dot (.) and then try to fetch the elmenents that in that array. so if you'd do array_get($array, 'foo'); it would be as if you'd type $array['foo']. But if the variable is set in the array, it will return it's value. null is a valid value, but not one you're likely to find in a $_POST array.

But if you also wish to filter out the null values I do recommend using a manual check instead of a catch all. Sometimes you want that null. But if you need a function for it I suggest modifying the above function to

if ( ! function_exists('array_get'))
{
    /**
     * Get an item from an array using "dot" notation.
     *
     * @param  array   $array
     * @param  string  $key
     * @param  mixed   $default
     * @return mixed
     */
    function array_get($array, $key, $default = null)
    {
        if (is_null($key)) return $array;
        if (isset($array[$key])) {
            $value = $array[$key];
            /**
             * Here is the null check. You can also add empty checks and other checks.
             */
            if(is_null($value)) {
               return $default;
            }
            return $value
        }
        foreach (explode('.', $key) as $segment)
        {
            if ( ! is_array($array) || ! array_key_exists($segment, $array))
            {
                return $default;
            }
            $array = $array[$segment];
        }
        return $array;
    }
}

Then you can simply use

array_get($_POST,'abc','some default value');

That way you don't have to worry if it's intantiated or not.

Added bonus is, if you have nested arrays, this makes it easy to access them without having to worry if the lower arrays are initiated or not.

$arr = ['foo' => ['bar' => ['baz' => 'Hello world']]];

array_get($arr, 'foo.bar.baz', 'The world has ended');
array_get($arr, 'foo.bar.ouch', 'The world has ended');

I use:

$x = @$_POST['x'];

Often I want more than just a default value, so I do one of:

if ($x) { ... }          // if it can be treated like a boolean
if (! empty($x)) { ... } // for cases where empty string, but not NULL, is possible
if (isset($x)){ ... }    // just checks for presence