Re-understand the php array_merge function, phparraymerge_PHP tutorial

Reunderstand the php array_merge function, phparraymerge

Re-understand the php array_merge function

Today I re-examined the array_merge() function due to a bug.

Definition: array_merge — merge one or more arrays

Specification: array array_merge(array $array1 [, array $...])

Description:

1. Combine the cells of one or more arrays, and the values ​​in one array are appended to the end of the previous array.

2. If the input array has the same string key name, the value after the key name will overwrite the previous value. However, if the array contains numeric keys, the subsequent values ​​will not overwrite the original values, but will be appended to them. 

3. If only an array is given and the array is numerically indexed, the key names will be re-indexed in a continuous manner.

This function has detailed examples in the manual and is also very versatile and practical.

A problem I encountered today was a warning in the manual, but I didn't notice it before, which resulted in a fatal error. As follows:

PHP >= Version 5.0, array_merge() only accepts array type parameters. However, you can use casts to combine other types.

Pay attention to the array variables generated by foreach and other codes. Either initialize the variable to an empty array, or perform a forced conversion during merging. Otherwise, you will suffer a lot. Therefore, it is also a good idea to maintain a habit of initializing variables.

There are two cases of merging arrays in PHP

1. If the two arrays have the same string key name:

<?php
 
 $book1 = array('linux'=>'linux服务器配置与管理','php'=>'PHP程序设计');
 $book2 = array('linux'=>'服务器配置与管理','jsp'=>'PHP'); 
 
 $result = array_merge($book1,$book2);
 print_r($result);
?>

The output is:

Array ( [linux] => 服务器配置与管理 [php] => PHP程序设计 [jsp] => PHP )

Note that the latter will replace the former. But if array_merge_recursive() is used, it can be retained and exist as a subarray. Such as:

<?php
 
 $book1 = array('linux'=>'linux服务器配置与管理','php'=>'PHP程序设计');
 $book2 = array('linux'=>'服务器配置与管理','jsp'=>'PHP'); 
 
 $result = array_merge_recursive($book1,$book2);
 print_r($result);
?>

The output is:

Array ( [linux] => Array ( [0] => linux服务器配置与管理 [1] => 服务器配置与管理 ) [php] => PHP程序设计 [jsp] => PHP )

2. If the two arrays have the same numerical key name:

<?php
 
 $book1 = array('linux服务器配置与管理','PHP程序设计');
 $book2 = array('服务器配置与管理','PHP'); 
 
 $result = array_merge($book1,$book2);
 print_r($result);
?>

The result is:

Array ( [0] => linux服务器配置与管理 [1] => PHP程序设计 [2] => 服务器配置与管理 [3] => PHP )

At this time, if the array contains the same numeric key name, the subsequent key values ​​will not overwrite the previous values, but the subsequent key values ​​will increase in order and be appended to the end. Do you understand? ^_^

1. The easiest way: use +

The following code:

<?php
$r1 = array('a'=>1,'b '=>3,'c'=>5,'d'=>7,'e'=>9);
$r2 = array('f'=>2,'g' =>4,'h'=>6,'i'=>8,'j'=>10);
$r = $r1+$r2;
echo '<pre> ';
print_r($r);
echo '</pre>';
?>
Code output result:
Array
(
[a] => 1
[b] => 3
[c] => 5
[d] => 7
[e] => 9
[f] => 2
[g] => 4
[h] => 6
[i] => 8
[j] => 10
)

But there is something to note about this method: only one element with the same two keywords will be retained, that is, $r1+r2, then the data in $r1 will be retained. This may also be used in special occasions. Maybe.

2. Use array_merge() function:

<?php
$array1 = array("color" => "red", 2, 4);
$array2 = array("a", "b", "color" => "green", "shape" => "trapezoid", 4);
$result = array_merge($array1, $array2) ;
print_r($result);
?>
Code output result:
Array
(
[color] => green
[0] => 2
[1] => 4
[2] => a
[3] => b
[shape] => trapezoid
[4] => 4
)

This is a function call by address. $array is a variable. What is passed to test() is the address of $array. The function directly rewrites the content of $array and returns the value