What is the application of json in php? (code example)

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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 first look at an example of array conversion:

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

The result is: {"a":1,"b":2,"c":3,"d":4,"e":5}<span class="token punctuation"><span class="token string"><span class="token punctuation"><span class="token number"><span class="token punctuation"><span class="token string"><span class="token punctuation"><span class="token number"><span class="token punctuation"><span class="token string"><span class="token punctuation"><span class="token number"><span class="token punctuation"><span class="token string"><span class="token punctuation"><span class="token number"><span class="token punctuation"><span class="token string"><span class="token punctuation"><span class="token number">#　<span class="token punctuation"></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>#Look at another example of object conversion ：

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

The result is: {"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 stores "value" (value) array), and 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, now there is an index array

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

结果为：["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"}

<span class="token punctuation"><span class="token string"><span class="token punctuation"><span class="token string"><span class="token punctuation"><span class="token string"><span class="token punctuation"><span class="token string"><span class="token punctuation"><span class="token string">##　<span class="token punctuation"><span class="token string"><span class="token punctuation"></span></span></span></span></span></span></span></span></span></span> </span></span></span>##Note that the data format has 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:

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"}

<span class="token punctuation"><span class="token string"><span class="token punctuation"><span class="token string"><span class="token punctuation"></span></span></span></span></span>## <span class="token punctuation"><span class="token string"><span class="token punctuation"><span class="token string"><span class="token punctuation"></span></span></span>can be seen,</span>Except for public variables (public), other things (constants, private variables, methods, etc.) are lost. </span>

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)[2]
  public 'a' => int 1
  public 'b' => int 2
  public 'c' => int 3
  public 'd' => int 4
  public '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 (size=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 Yes, 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.

第一个的错误是，json的分隔符（delimiter）只允许使用双引号，不能使用单引号。

第二个的错误是，json名值对的"名"（冒号左边的部分），任何情况下都必须使用双引号。

第三个的错误是，最后一个值之后不能添加逗号（trailing comma）。
另外，json只能用来表示对象（object）和数组（array），如果对一个字符串或数值使用json_decode()，将会返回null。

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

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