How to use the json_php technique correctly in PHP

Starting with version 5.2, PHP native provides Json_encode () and Json_decode () functions, which are used for encoding and decoding.

1, 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);

The output from the above code is:
{"A": 1, "B": 2, "C": 3, "D": 4, "E": 5}

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

Copy Code code as follows:

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

The output of the above code is:

Copy Code code as follows:

{
"Body": "Another Post",

"id": 21,

"Approved": TRUE,

"Favorite_count": 1,

' Status ': null
}

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.

2. Indexed 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 indexes:
$arr = Array (' One ', ' two ', ' three ');
echo Json_encode ($arr);

The output 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 is changed:
{"1": "One", "2": "Two", "3": "Three"}

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);

3, classes (class) of the conversion
The following is a class of PHP:

Copy Code code as follows:

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:

Copy Code code as follows:

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

The output results are:
{' PUBLIC_EX ': ' This is public '}

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

4, Json_decode ()
This function is used to convert JSON text to the appropriate PHP data structure. Here is an example:

Copy Code code as follows:

$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:

Copy Code code 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 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:

Copy Code code as follows:

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

5, Json_decode () Common errors
The following three kinds of JSON are all wrong, can you see what's wrong?

Copy Code code as follows:

$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