What Types of Data Can Be Used as Array Keys in PHP?

Two types of data can be used as array keys: string and integer. When a string is used as a key and the string represent an integer, PHP will convert the string into a integer and use it as the key. Here is a PHP script on different types of keys:

<?php 
$mixed = array();
$mixed["Zero"] = "PHP";
$mixed[1] = "Perl";
$mixed["Two"] = "Java";
$mixed["3"] = "C+";
$mixed[""] = "Basic";
print("Array with mixed keys:\n");
print_r($mixed);
print("\$mixed[3] = ".$mixed[3]."\n");
print("\$mixed[\"3\"] = ".$mixed["3"]."\n");
print("\$mixed[\"\"] = ".$mixed[""]."\n");
?>

This script will print:

Array with mixed keys:
Array
(
    [Zero] => PHP
    [1] => Perl
    [Two] => Java
    [3] => C+
    [] => Basic
)
$mixed[3] = C+
$mixed["3"] = C+
$mixed[""] = Basic

Note that an empty string can also be used as a key.

⇒Understanding PHP Arrays and Their Basic Operations

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