How to determine if all array elements are null in php

Judgment steps: 1. Use the array_filter() function to call the callback function to filter the array and return null elements. The syntax function f($n){return(is_null($n));}$res=array_filter( $arr,"f");"; 2. Use the count() function to get the lengths of the original array and the filtered array, and compare whether the lengths of the two arrays are equal. If they are equal, they will both be null, and if they are returned, there will be other elements.

The operating environment of this tutorial: windows7 system, PHP version 8.1, DELL G3 computer

In php, you can use array_filter(), count( ) and is_null() functions to determine whether the array element is null.

Implementation steps:

Step 1: Use array_filter() and is_null() functions Filter the array and return the null elements in the array

• array_filter() function uses the callback function to filter the elements in the array and returns a filtered array. This function converts the input array into Each key value in is passed to the callback function. If the callback function returns true, the current key value in the input array is returned to the result array. The array key name remains unchanged.

• The is_null() function is used to detect whether a variable is NULL. If the specified variable is NULL, it returns TRUE, otherwise it returns FALSE.

<?php
header(&#39;content-type:text/html;charset=utf-8&#39;);   
function f($num){
	 return(is_null($num));
}
$arr=array(2,null,4,"null",1,null,9);
var_dump($arr);
$res=array_filter($arr,"f");
echo "数组中的null元素：";
var_dump($res);
?>

Step 2: Use the count() function to obtain the length of the original array and the filtered array, and compare whether the lengths of the two arrays are equal

数组长度1==数组长度2

• If the lengths of the two arrays are not equal, then Not all

• If the two arrays are of equal length, they are both

Implementation code:

<?php
header(&#39;content-type:text/html;charset=utf-8&#39;);   
function f($num){
	 return(is_null($num));
}
$arr=array(2,null,4,"null",1,null,9);
var_dump($arr);
$res=array_filter($arr,"f");
echo "数组中的null元素：";
var_dump($res);
$len1=count($arr);
$len2=count($res);
if($len1==$len2){
	echo "数组元素都为null";
}else{
	echo "数组元素中不都为null，有其他元素";
}
?>

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