PHP中array_merge和array+array的区别

<?php
echo "<pre>";

/*
 *****************
 * 如果key是字符串 *
 *****************
 */
$arr1 = [
    'name' => 'zhangsan',
    'age' => '28',
];
$arr2 = [
    'name' => 'lisi',
    'age' => '17',
];
//如果键名为字符，且键名相同，array_merge()最后面的元素值会覆盖前面的元素值
print_r(array_merge($arr1, $arr2));
/*
Array
(
    [name] => lisi
    [age] => 17
)
*/


//PHP中还有一个函数：array_merge_recursive
//递归地合并一个或多个数组，如果输入的数组中有相同的字符串键名，则这些值会被合并到一个数组中去
print_r(array_merge_recursive($arr1, $arr2));
/*
Array
(
    [name] => Array
        (
            [0] => zhangsan
            [1] => lisi
        )

    [age] => Array
        (
            [0] => 28
            [1] => 17
        )

)
 */

//如果键名为字符，且键名相同，两个数组相加会将最先出现的元素值作为结果
print_r($arr1 + $arr2);
/*
Array
(
    [name] => zhangsan
    [age] => 28
)
*/

//两个数组的key的个数不相同
$arr1 = [
    'name' => 'zhangsan',
    'age' => '28',
];
$arr2 = [
    'name' => 'lisi',
    'age' => '17',
    'sex' => 'nan',
];
print_r(array_merge($arr1, $arr2));
/*
Array
(
    [name] => lisi
    [age] => 17
    [sex] => nan
)
 */

print_r($arr1 + $arr2);
/*
Array
(
    [name] => zhangsan
    [age] => 28
    [sex] => nan
)
*/

echo "<hr>";

/*
 ***************
 * 如果key是数字 *
 ***************
 */
$arr1 = ['zhangsan','28'];
$arr2 = ['lisi','17'];

//如果键名为数字，array_merge()不会进行覆盖，但是会覆盖掉前面相同键值
print_r(array_merge($arr1,$arr2));
/*
Array
(
    [0] => zhangsan
    [1] => 28
    [2] => lisi
    [3] => 17
)
*/

//如果键名为数字，数组相加会将最先出现的值作为结果，后面键名相同的会被抛弃
print_r($arr1+$arr2);
/*
Array
(
    [0] => zhangsan
    [1] => 28
)
*/

//再比如
$arr1 = [3=>'zhangsan',9=>'28'];
$arr2 = [3=>'lisi',9=>'17',12=>'nan'];

//array_merge()会覆盖掉前面相同键值，重新从0开始进行键排序
print_r(array_merge($arr1,$arr2));
/*
Array
(
    [0] => zhangsan
    [1] => 28
    [2] => lisi
    [3] => 17
    [4] => nan
)
*/

//数组相加 不会对键进行重新排序
print_r($arr1+$arr2);
/*
Array
(
    [3] => zhangsan
    [9] => 28
    [12] => nan
)
*/