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Use and conversion of JSON in php, use and conversion of phpJSON

I have written a simple example of returning json data in php before. I just went online and suddenly found an article that also introduced json. It was quite detailed and worth reference. The content is as follows

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()

Copy code The code is as follows:

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

Output

Copy code The code is as follows:

{"a":1,"b":2,"c":3,"d":4,"e":5}

Look at another example of object conversion:

Copy 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);

Output

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 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. Index array and associative array

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

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

Copy code The code is as follows:

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

Output

Copy code The code is as follows:

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

If you change it to an associative array:

Copy code The code is as follows:

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

The output becomes

Copy code The code is as follows:

{"1":"one","2":"two","3":"three"}

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

Copy code The code is as follows:

json_encode( (object)$arr );

or

Copy code The code is as follows:

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 code The code is as follows:

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

The output result is

Copy code The code is as follows:

{"public_ex":"this is public"}

You can see that 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 object, not an array. For example:

Copy code The code is as follows:

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

Copy code The code is as follows:

$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';
var_dump(json_decode($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. Can you see where the error is?

Copy code The code is as follows:

$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 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.

Copy code The code is as follows:

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

The above is the entire content of this article. I hope you all like it and gain something after reading it

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