PHP JSON usage examples

1. json_encode()

This function is mainly used to convert arrays and objects into json format. Let’s look at an example of array conversion first:

   $arr = array ('a'=>1,'b'=>2,'c'=>3,'d'=>4,'e'=>5);　　
echo json_encode($arr);　　

The result is

{"a":1,"b":2,"c":3,"d":4,"e":5}　

Look at another object Conversion example:

   $obj->body           = 'another post';　　
$obj->id             = 21;　　
$obj->approved       = true;　　
$obj->favorite_count = 1;　　
$obj->status         = NULL;　　
echo json_encode($obj);　　
   结果为
{　　　　"body":"another post",　　
　　"id":21,　　
　　"approved":true,　　
　　"favorite_count":1,　　
　　"status":null　　} 　

Since json only accepts utf-8 encoded characters, the parameters of json_encode() must be utf-8 encoded, otherwise you will get empty characters or null. When Chinese uses GB2312 encoding, or foreign languages ​​use ISO-8859-1 encoding, special attention should be paid to this point.

2. Indexed arrays and associative arrays

PHP supports two types of arrays, one is an indexed array that only saves "value" (value), and the other is a "name/value pair" that is saved ) is an associative array.

Since javascript does not support associative arrays, json_encode() only converts the indexed array to array format, and converts the associative array to object format.

For example, now there is an index array

   
$arr = Array('one', 'two', 'three');　　
echo json_encode($arr);　　

The result is:

["one","two","three"] 

If you change it to an associative array:

　　$arr = Array('1'=>'one', '2'=>'two', '3'=>'three');
 　　
　　echo json_encode($arr);　　

The result changes:

{"1":"one","2":"two","3":"three"} ​

Note that the data format has changed from "[]" (array) to "{}" (object ).

If you need to force "index array" to be converted into "object", you can write like this

json_encode( (object)$arr );　　

or

json_encode ( $arr, JSON_FORCE_OBJECT );　　

3. Conversion of class

The following is a PHP class:

　　class Foo {　　
　　　　const     ERROR_CODE = '404';　　
　　　　public    $public_ex = 'this is public';　　
　　　　private   $private_ex = 'this is private!';　　
　　　　protected $protected_ex = 'this should be protected'; 
 　　
　　　　public function getErrorCode() {　　
　　　　　　return self::ERROR_CODE;　　
　　　　}　　
　　}　　

Now, perform json conversion on the instance of this class:

$foo = new Foo;　　
$foo_json = json_encode($foo);　　
echo $foo_json;　　

The output result is

{"public_ex":"this is public"} ​

You can see that in addition to public variables (public), other things (constants, Private variables, methods, etc.) are lost.

4. json_decode()

This function is used to convert json text into the corresponding PHP data structure. Here is an example:

   
　　$json = '{"foo": 12345}';
 　　
　　$obj = json_decode($json);　　
　　print $obj->{'foo'}; // 12345　　

Normally, json_decode() always returns a PHP object, not an array. For example:

   
　　$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';
 　　
　　var_dump(json_decode($json));　　

The result is to generate a PHP object:

object(stdClass)#1 (5) {　　
　　["a"] => int(1)　　　　["b"] => int(2)　　　　["c"] => int(3)　　　　["d"] => int(4)　　　　["e"] => int(5)　　
}　　

If you want to force the generation of a PHP associative array, json_decode() needs to add a parameter true:

   
　　$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';
 　　
　　var_dump(json_decode($json,true));　　

The result is an associative array:

   
array(5) {　　
 　　["a"] => int(1)　　 　　["b"] => int(2)　　 　　["c"] => int(3)　　 　　["d"] => int(4)　　 　　["e"] => int(5)　　
}　　

5. json_decode() Common mistakes

The following three ways of writing json are all wrong. Can you see where the error is?

$bad_json = "{ 'bar': 'baz' }";　　
$bad_json = '{ bar: "baz" }';　　
$bad_json = '{ "bar": "baz", }';　　

Executing json_decode() on these three strings will return null and report an error.

The first mistake is that the json delimiter only allows the use of double quotes, not single quotes. The second mistake is that the "name" of the json name-value pair (the part to the left of the colon) must be used in double quotes under any circumstances. The third error is that you cannot add a trailing comma after the last value.

In addition, json can only be used to represent objects and arrays. If json_decode() is used on a string or value, null will be returned.

var_dump(json_decode("Hello World")); //null