PHP Json_encode and json_decode details and examples _php examples

One, Json_encode ()

This function is used primarily to convert arrays and objects into JSON format. Let's look at an example of an array conversion:

$arr = Array (' A ' =>1, ' B ' =>2, ' C ' =>3, ' d ' =>4, ' e ' =>5);
Echo Json_encode ($arr);

Result is

{"A": 1, "B": 2, "C": 3, "D": 4, "E": 5}

Let's look at an example of an object conversion:

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

Result is

{"Body": "Another post",
"id": "
Approved": True,
"Favorite_count": 1,

Since JSON only accepts UTF-8 encoded characters, the Json_encode () argument must be utf-8 encoded, or it will get null characters or NULL. Special attention should be paid to the use of GB2312 encoding in Chinese, or the use of iso-8859-1 encoding in foreign languages.

index arrays and associative arrays

PHP supports two types of arrays, one is the index array (indexed array) that holds only the value, the other is an associative array (associative array) that holds the name value pair (name/value).

Because JavaScript does not support associative arrays, json_encode () only converts an indexed array (indexed array) into an array format and an associative array (associative array) into object format.

For example, now there is an array of indices

$arr = Array (' One ', ' two ', ' three ');
Echo Json_encode ($arr);

The results are:

["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 is changed:

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

If you need to force an "indexed array" into an "object", you can write

Json_encode ((object) $arr);

Or

Json_encode ($arr, json_force_object);

Classes (Class) conversion

The following is a class of PHP:

Class Foo {
const   error_code = ' 404 ';　　
public  $public _ex = ' it is public ';　　
private  $private _ex = ' this is private! ';　　　　
protected $protected _ex = ' This should to be protected ';
Public Function GetErrorCode () {return
self::error_code;　　
}
}　　

Now, make a JSON conversion to an instance of this class:

$foo = new Foo;　　
$foo _json = Json_encode ($foo);
echo $foo _json;

The output result is

As you can see, other things (constants, private variables, methods, and so on) are lost in addition to exposing variables (public).

Iv. Json_decode ()

This function is used to convert JSON text to the appropriate PHP data structure. Here is an example:

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

Typically, Json_decode () always returns a PHP object, not an array. Like what:

$json = ' {' A ': 1, "B": 2, "C": 3, "D": 4, "E": 5} ';
Var_dump (Json_decode ($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 a PHP associative array to be generated, 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));　　

As a result, an associative array is generated:

Array (5) {
 ["a"] => int (1) ["B"] => int (2) ["C"] => int (3) ["D"] => int (4) ["E"] => Int (5)
}
 

V. Common errors in Json_decode ()

The following three kinds of JSON are all wrong, can you see what's wrong?

$bad _json = "{' Bar ': ' Baz '}";　　
$bad _json = ' {bar: ' Baz '} ';
$bad _json = ' {' bar ': ' Baz ',} ';

Performing Json_decode () on these three strings will return null and have an error.

The first error is that the JSON delimiter (delimiter) only allows double quotes and cannot use single quotes. The second error is the name of the JSON name value pair (the part to the left of the colon), which must be used in double quotes in any case. The third error is that a comma (trailing comma) cannot be added after the last value.

In addition, JSON can only be used to represent objects (object) and Arrays (array), and null will be returned if Json_decode () is used for a string or numeric value.

Var_dump (Json_decode ("Hello World")); Null

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