A detailed explanation of the array_change_key_case() function in PHP

array_change_key_case() Converts all keys of the array to uppercase letters:

<?php 
/* 
 array_change_key_case() 返回其键均为大写或小写的数组。 
 array array_change_key_case(array input[,int case]) 
 参数描述：array是要转换键值的数组 
     case有两个选项:CASE_LOWER，默认选项，以小写字母返回数组的键 
             CASE_UPPER,以大写字母返回数组的键 
 */
$input_array = array(&#39;a&#39;=>&#39;Java&#39;,  
           &#39;B&#39;=>&#39;Php&#39;,  
           &#39;c&#39;=>&#39;C++&#39;,  
           &#39;D&#39;=>&#39;C#&#39;); 
print_r(array_change_key_case($input_array, CASE_LOWER)); 
print_r(array_change_key_case($input_array, CASE_UPPER)); 
//如果在运行该函数时两个或多个键相同，则最后的元素会覆盖其他元素，例如： 
$input_array = array(&#39;a&#39;=>&#39;Barcelona&#39;,  
           &#39;B&#39;=>&#39;Madrid&#39;,  
           &#39;c&#39;=>&#39;Manchester&#39;,  
           &#39;b&#39;=>&#39;Milan&#39;); 
print_r(array_change_key_case($input_array, CASE_LOWER)); 
?>

Definition and usage

array_change_key_case() function converts all keys of the array to uppercase letters or lowercase letter.

Syntax

array_change_key_case(array,case);

Parameters

Description

array Required. Specifies the array to use.

case Optional. Possible values:

CASE_LOWER - Default value. Convert an array's keys to lowercase letters.

CASE_UPPER - Convert array keys to uppercase letters.

Technical Details

Return value:

Returns an array with keys with lowercase letters, or returns with uppercase letters An array of letters with keys, or FALSE if array is not an array.

PHP version:

4.2+

Convert all keys of the array to lowercase letters:

<?php
$age=array("Peter"=>"35","Ben"=>"37","Joe"=>"43");
print_r(array_change_key_case($age,CASE_LOWER));
?>

If after running array_change_key_case() there are two or more keys with the same key (such as "b" and "B"), the last element will overwrite the other elements:

<?php
$pets=array("a"=>"Cat","B"=>"Dog","c"=>"Horse","b"=>"Bird");
print_r(array_change_key_case($pets,CASE_UPPER));
?>

More examples :

$cc = [
            '0'=>[
                'Abc'=>'asdfasdf',
                'BBAbc'=>'asdfasdf',
                'AbDDc'=>'asdfasdf',
                
            ]
        ];
        $tmp = array_change_key_case($cc);
        dump($tmp);
        return;

The printout result is

array (size=1)
  0 => 
    array (size=3)
      'Abc' => string 'asdfasdf' (length=8)
      'BBAbc' => string 'asdfasdf' (length=8)
      'AbDDc' => string 'asdfasdf' (length=8)

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