How to add elements to the head of an array in php

Two methods: 1. Use array_unshift() to add one or more elements to the header, the syntax is "array_unshift(array, value 1, value 2...)"; 2. Use array_splice( ), syntax "array_splice(array,0,0,single value or array)".

The operating environment of this tutorial: Windows 7 system, PHP version 8.1, DELL G3 computer

php is in the array header Methods to add elements from the bottom

1. Use the array_unshift() function

The array_unshift() function can insert one or more elements at the beginning of the array New element (key value).

array_unshift($array,$value1,$value2...)

Let’s take a closer look at the following example:

<?php
$arr=array(10,12,20);
array_unshift($arr,8,"9");
var_dump($arr);
?>

array_unshift($arr,8,9)It can be seen that it is inserted at the beginning of the $arr array Two new elements: the numerical value "8" and the string "9", so the output result is:

array_unshift( ) function will not maintain the original numerical index relationship, but will delete all numerical key names and reassign them, that is, count again from 0; but all string key names will remain unchanged.

<?php
header("Content-type:text/html;charset=utf-8");
$arr=array("a"=>"red","b"=>"green",3=>"pink");
echo "原来的数组：";
var_dump($arr);
array_unshift($arr,"blue");
echo "在开头插入一个新元素后：";
var_dump($arr);
?>

Output result:

#2. Use array_splice() function

array_splice() function is a A powerful function that can be used to delete array elements, replace array elements, and insert array elements (just set the parameter $length to 0).

array_splice($array,$start,$length,$value)

When $length=0, then the parameter $start can specify the position (subscript) to start inserting, and the parameter $value You can specify the insertion value (if there are multiple values, you need to set it as an array).

If you want to add elements at the beginning, the value of $start needs to be 0.

<?php
header("Content-type:text/html;charset=utf-8");
$arr1=array(10,12,20);
var_dump($arr1);
array_splice($arr1,0,0,"1");
var_dump($arr1);

$arr2=array(10,12,20);
array_splice($arr2,0,0,array("1",25,"3"));
var_dump($arr2);
?>

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