Awesome function I came across awhile back to fix issues in php when debugging is giving you undefined variables. Whatever is undefined just replace with exst(). For example if variable $xyz is undefined replace it with exst($xyz) and it will not longer return errors. While it's better to write your code in a way to avoid this, it's an easy way …

readme.md

These check if variable isset or not

function is_set( & $variable ) { if ( isset( $variable ) and ! is_null( $variable ) ) return true; else return false; }

if(!empty($_POST[myField])) { //Do my PHP code }

null

if (isset($var) && ($var === true)) { ... } array_key_exists('v', $GLOBALS)

isset()

isset — Determine if a variable is set and is not NULL

In other words, it returns true only when the variable is not null.

empty()

empty — Determine whether a variable is empty

In other words, it will return true if the variable is an empty string, false, array(), NULL, “0?, 0, and an unset variable.

is_null()

https://www.virendrachandak.com/techtalk/php-isset-vs-empty-vs-is_null/

https://gist.github.com/JeffreyWay/3194444

alternative_variable_defining_methods.php

<?php

// recommended solution
$user_name = $_SESSION['user_name'];
if (empty($user_name)) $user_name = '';

// OR 

// just define at the top of the script index.php
$user_name = ''; 
$user_name = $_SESSION['user_name'];

// OR 

$user_name = $_SESSION['user_name'];
if (!isset($user_name)) $user_name = '';

exists.php

/** 
 * Function exst() - Checks if the variable has been set 
 * (copy/paste it in any place of your code)
 * 
 * If the variable is set and not empty returns the variable (no transformation)
 * If the variable is not set or empty, returns the $default value
 *
 * @param  mixed $var
 * @param  mixed $default
 * 
 * @return mixed 
 *
 * Example
 * $greeting = "Hello, ".exst($user_name, 'Visitor')." from ".exst($user_location);
 */

function exst( & $var, $default = "")
{
    $t = "";
    if ( !isset($var)  || !$var ) {
        if (isset($default) && $default != "") $t = $default;
    }
    else  {  
        $t = $var;
    }
    if (is_string($t)) $t = trim($t);
    return $t;
}