Introduction to the application of JSON in PHP_PHP tutorial-PHP Tutorial-php.cn

Introduction to the application of JSON in PHP_PHP tutorial

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Release： 2016-07-21 15:16:56

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Starting from version 5.2, PHP natively provides json_encode() and json_decode() functions, the former is used for encoding, and the latter is used for decoding.
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 example of object conversion:

Copy the code The code is as follows:

 
　$ obj->body = 'another post'; 
 $obj->id = 21; 
 $obj->approved = true; 
 $obj->favorite_count = 1; 
 $obj->status = NULL; 
 echo json_encode($obj); 

The result is

Copy code The code is as follows:

 
 { 
 "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 character 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 stores "value" (value), The other is an associative array that stores name/value pairs.
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, there is now an index array

Copy code The code is as follows:

 
　$arr = Array('one' , 'two', 'three'); 
 echo json_encode($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 The format changed from "[]" (array) to "{}" (object).
If you need to force "index array" into "object", you can write like this
json_encode( (object)$arr );
or
json_encode ( $arr, JSON_FORCE_OBJECT );

3. Class conversion

The following is a PHP class:

Copy code The code is as follows:

 
 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: 

Copy the code

The code is as follows:

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

 
The output result is 
　{"public_ex":"this is public"} 
Yes See, except for public variables (public), other things (constants, private variables, methods, etc.) are missing. 

4. json_decode()

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

Copy code
The code is as follows:

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

 
Normally, json_decode() always returns a PHP objects, not arrays. 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: 

Copy code

The code is as follows:

 
 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 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:

Copy Code The code is as follows:

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

5. Common errors of json_decode()

The following three ways of writing json are all wrong. You can see the mistakes Where?

Copy code The code is as follows:

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

Execute json_decode( on these three strings ) will return null and report an error.
The first error is that the json delimiter only allows the use of double quotes, not single quotes. The second mistake is that the "name" (the part to the left of the colon) of the json name-value pair must use double quotes in any case. 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