PHP - Checking if array index exist or is null

问题

Is there a way to check if an array index exists or is null? isset() doesn't tell you whether the index doesn't exist or exists but is null. If I do : isset($array[$index]) || is_null($array[$index]) it won't work because if the index doesn't exist is_null will crash.

How can I check this please? Also is there a way to check only if something exist, no matter if it is set to null or not?

回答1:

The function array_key_exists() can do that, and property_exists() for objects, plus what Vineet1982 said. Thanks for your help.

回答2:

This is the very good question and you can use get_defined_vars() for this:

$foo = NULL;
$a = get_defined_vars();

if (array_key_exists('def', $a)) {
   // Should evaluate to FALSE
 }; 

if (array_key_exists('foo', $a)) {
   // Should evaluate to TRUE
};

This will solve your problem

回答3:

Simplest defined in: http://php.net/manual/en/function.array-key-exists.php

<?php
$array=array('raja'=>'value', 'john'=>'value2');
$var='raja';
echo array_key_exists($var, $array);
?>

来源：https://stackoverflow.com/questions/15310261/php-checking-if-array-index-exist-or-is-null