PHP: Strange Array Behaviour After Object Type Casting to Array

问题

When you do array type-casting of json_decoded value (with $assoc = false), PHP creates an array with string indices:

$a = (array)json_decode('{"7":"value1","8":"value2","9":"value3","13":"value4"}');

var_export($a);

//array (
//  '7' => 'value1',
//  '8' => 'value2',
//  '9' => 'value3',
//  '13' => 'value4',
//)

And for some reason these indices are not accessible:

var_dump(isset($a[7]), isset($a['7']));

//false
//false

When you try to create the same array by PHP itself, it is being created with numeric indices (string are automatically converted), and values are accessible using both strings and numbers:

$c = array('7' => 'value1', '8' => 'value2', '9' => 'value3','10' => 'value4');

var_export($c);

var_dump(isset($c[7]), isset($c['7']));

//array (
//  7 => 'value1',
//  8 => 'value2',
//  9 => 'value3',
//  13 => 'value4',
//)
//
//true
//true

Does anybody know what is going on here? Is it some bug of older PHP versions (the issue seems to be fixed on PHP version >= 7.2, but I can't find anything related in changelog)?

Here's the demo of what is going on: https://3v4l.org/da9CJ.

回答1:

This seems to be related to bug #61655 fixed in 7.2.0:

in a object property lookup by name always in string, but in array numeric string(like "22200" ) key will transform to numeric but not a string anymore. when conversion internal HashTable did't changed so after conversion, key lookup will fail.

Clarified: $a["2000"] is always interpreted as $a[2000], but (array) failed to cast object string keys to numbers. So the array contained string numeric indices, but the array syntax' automatic casting prevented those from being accessible.

回答2:

add TRUE to json_decode()

<?php
$a = json_decode('{"7":"value1","8":"value2","9":"value3","13":"value4"}',TRUE);

var_export($a);

var_dump(isset($a[7]), isset($a['7']));

https://3v4l.org/YuF9B

回答3:

add TRUE to json_decode() is possible, but it will couse to recode everything.

Becouse you have to change the access to the variables.

if your json look like this:

$return = '{"status":"ok","message":"","code":"200","data":{"1234":{"sid":1,"name":"foo"},"4321":{"sid":2,"name":"bar"}}}';

on:

$json_data = json_decode($return, true);
$data = $json_data['data'];

you can loop the $data and have to access the values as array: $data[0]['name'] ...

on:

$json_data = json_decode($return);
$data = (array) $json_data->data;

you can loop the $data and have to access the values as objects: $data[0]->name ...

来源：https://stackoverflow.com/questions/48379891/php-strange-array-behaviour-after-object-type-casting-to-array