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json_encode

(PHP 5 >= 5.2.0, PHP 7, PHP 8, PECL json >= 1.2.0)

json_encode — 对变量进行 JSON 编码

说明

json_encode(mixed $value, int $flags = 0, int $depth = 512): string|false

返回字符串，包含了 value 值 JSON 形式的表示。如果参数是 array 或 object，则会递归序列化。

如果要序列化的值是对象，则默认仅包含公开可见的属性，或者类可以实现 JsonSerializable 控制其值如何序列化为 JSON。

编码受传入的 flags 参数影响，此外浮点值的编码依赖于 serialize_precision。

参数

value

待编码的 value ，除了 resource 类型之外，可以为任何数据类型。

所有字符串数据的编码必须是 UTF-8。

注意:
PHP 实现了 JSON 的一个超集，参考 » RFC 7159.

flags

由以下常量组成的二进制掩码： JSON_FORCE_OBJECT、 JSON_HEX_QUOT、 JSON_HEX_TAG、 JSON_HEX_AMP、 JSON_HEX_APOS、 JSON_INVALID_UTF8_IGNORE、 JSON_INVALID_UTF8_SUBSTITUTE、 JSON_NUMERIC_CHECK、 JSON_PARTIAL_OUTPUT_ON_ERROR、 JSON_PRESERVE_ZERO_FRACTION、 JSON_PRETTY_PRINT、 JSON_UNESCAPED_LINE_TERMINATORS、 JSON_UNESCAPED_SLASHES、 JSON_UNESCAPED_UNICODE、 JSON_THROW_ON_ERROR。关于 JSON 常量详情参考 JSON 常量页面。

depth

设置最大深度。必须大于0。

返回值

成功则返回 JSON 编码的 string 或者在失败时返回 false 。

更新日志

版本	说明
7.3.0	`flags` 参数新增 `JSON_THROW_ON_ERROR` 常量。
7.2.0	`flags` 参数新增 `JSON_INVALID_UTF8_IGNORE` 和 `JSON_INVALID_UTF8_SUBSTITUTE` 常量。
7.1.0	`flags` 参数新增 `JSON_UNESCAPED_LINE_TERMINATORS` 常量。
7.1.0	对 float 值进行编码时，使用 serialize_precision 代替 precision。

示例

示例 #1 json_encode() 例子

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

echo json_encode($arr);
?>

以上示例会输出：

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

示例 #2 json_encode() 函数中 flags 参数的用法

<?php
$a = array('<foo>',"'bar'",'"baz"','&blong&', "\xc3\xa9");

echo "Normal: ",  json_encode($a), "\n";
echo "Tags: ",    json_encode($a, JSON_HEX_TAG), "\n";
echo "Apos: ",    json_encode($a, JSON_HEX_APOS), "\n";
echo "Quot: ",    json_encode($a, JSON_HEX_QUOT), "\n";
echo "Amp: ",     json_encode($a, JSON_HEX_AMP), "\n";
echo "Unicode: ", json_encode($a, JSON_UNESCAPED_UNICODE), "\n";
echo "All: ",     json_encode($a, JSON_HEX_TAG | JSON_HEX_APOS | JSON_HEX_QUOT | JSON_HEX_AMP | JSON_UNESCAPED_UNICODE), "\n\n";

$b = array();

echo "Empty array output as array: ", json_encode($b), "\n";
echo "Empty array output as object: ", json_encode($b, JSON_FORCE_OBJECT), "\n\n";

$c = array(array(1,2,3));

echo "Non-associative array output as array: ", json_encode($c), "\n";
echo "Non-associative array output as object: ", json_encode($c, JSON_FORCE_OBJECT), "\n\n";

$d = array('foo' => 'bar', 'baz' => 'long');

echo "Associative array always output as object: ", json_encode($d), "\n";
echo "Associative array always output as object: ", json_encode($d, JSON_FORCE_OBJECT), "\n\n";
?>

以上示例会输出：

Normal: ["<foo>","'bar'","\"baz\"","&blong&","\u00e9"]
Tags: ["\u003Cfoo\u003E","'bar'","\"baz\"","&blong&","\u00e9"]
Apos: ["<foo>","\u0027bar\u0027","\"baz\"","&blong&","\u00e9"]
Quot: ["<foo>","'bar'","\u0022baz\u0022","&blong&","\u00e9"]
Amp: ["<foo>","'bar'","\"baz\"","\u0026blong\u0026","\u00e9"]
Unicode: ["<foo>","'bar'","\"baz\"","&blong&","é"]
All: ["\u003Cfoo\u003E","\u0027bar\u0027","\u0022baz\u0022","\u0026blong\u0026","é"]

Empty array output as array: []
Empty array output as object: {}

Non-associative array output as array: [[1,2,3]]
Non-associative array output as object: {"0":{"0":1,"1":2,"2":3}}

Associative array always output as object: {"foo":"bar","baz":"long"}
Associative array always output as object: {"foo":"bar","baz":"long"}

示例 #3 选项 JSON_NUMERIC_CHECK 例子

<?php
echo "Strings representing numbers automatically turned into numbers".PHP_EOL;
$numbers = array('+123123', '-123123', '1.2e3', '0.00001');
var_dump(
 $numbers,
 json_encode($numbers, JSON_NUMERIC_CHECK)
);
echo "Strings containing improperly formatted numbers".PHP_EOL;
$strings = array('+a33123456789', 'a123');
var_dump(
 $strings,
 json_encode($strings, JSON_NUMERIC_CHECK)
);
?>

以上示例的输出类似于：

Strings representing numbers automatically turned into numbers
array(4) {
  [0]=>
  string(7) "+123123"
  [1]=>
  string(7) "-123123"
  [2]=>
  string(5) "1.2e3"
  [3]=>
  string(7) "0.00001"
}
string(28) "[123123,-123123,1200,1.0e-5]"
Strings containing improperly formatted numbers
array(2) {
  [0]=>
  string(13) "+a33123456789"
  [1]=>
  string(4) "a123"
}
string(24) "["+a33123456789","a123"]"

示例 #4 连续与非连续数组示例

<?php
echo "连续数组".PHP_EOL;
$sequential = array("foo", "bar", "baz", "blong");
var_dump(
 $sequential,
 json_encode($sequential)
);

echo PHP_EOL."非连续数组".PHP_EOL;
$nonsequential = array(1=>"foo", 2=>"bar", 3=>"baz", 4=>"blong");
var_dump(
 $nonsequential,
 json_encode($nonsequential)
);

echo PHP_EOL."删除一个连续数组值的方式产生的非连续数组".PHP_EOL;
unset($sequential[1]);
var_dump(
 $sequential,
 json_encode($sequential)
);
?>

以上示例会输出：

连续数组
array(4) {
  [0]=>
  string(3) "foo"
  [1]=>
  string(3) "bar"
  [2]=>
  string(3) "baz"
  [3]=>
  string(5) "blong"
}
string(27) "["foo","bar","baz","blong"]"

非连续数组
array(4) {
  [1]=>
  string(3) "foo"
  [2]=>
  string(3) "bar"
  [3]=>
  string(3) "baz"
  [4]=>
  string(5) "blong"
}
string(43) "{"1":"foo","2":"bar","3":"baz","4":"blong"}"

删除一个连续数组值的方式产生的非连续数组
array(3) {
  [0]=>
  string(3) "foo"
  [2]=>
  string(3) "baz"
  [3]=>
  string(5) "blong"
}
string(33) "{"0":"foo","2":"baz","3":"blong"}"

示例 #5 选项 JSON_PRESERVE_ZERO_FRACTION 的例子

<?php
var_dump(json_encode(12.0, JSON_PRESERVE_ZERO_FRACTION));
var_dump(json_encode(12.0));
?>

以上示例会输出：

string(4) "12.0"
string(2) "12"

注释

注意:
如果执行失败，可以通过 json_last_error() 函数来获取详细错误信息。

注意:
如果要编码的数组的键不是从0开始的数字，所有的键将会被当作字符串，并明确声明为 key-value 对。

注意:
参考 JSON 解析器，如果指定简单的 string、integer、float 或 boolean 作为输入 value，json_encode() 将生成简单的值的 JSON（既不是对象又不是数组）。虽然大多数解码器会接受这些值作为有效的 JSON，但有些可能不会，因为在这一点上规范是模棱两可的。

总而言之，应该测试下 JSON decoder 能否处理 json_encode() 生成的数据。

参见

JsonSerializable
json_decode() - 对 JSON 格式的字符串进行解码
json_last_error() - 返回最后发生的错误
serialize() - 生成值的可存储表示

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User Contributed Notes 9 notes

down

102

bohwaz ¶

12 years ago


Are you sure you want to use JSON_NUMERIC_CHECK, really really sure?

Just watch this usecase:

<?php
// International phone number
json_encode(array('phone_number' => '+33123456789'), JSON_NUMERIC_CHECK);
?>

And then you get this JSON:

{"phone_number":33123456789}

Maybe it makes sense for PHP (as is_numeric('+33123456789') returns true), but really, casting it as an int?!

So be careful when using JSON_NUMERIC_CHECK, it may mess up with your data!

down

elliseproduction at gmail dot com ¶

2 years ago


Notice that JSON_FORCE_OBJECT will convert all non-associative arrays to objects. This is not necessarily a good solution for empty arrays.
If you want to convert only empty arrays to objects, simply convert them to empty object before use json_encode function.

For example:

<?php

$foo=array(
   'empty2object'=>(object)[],
   'empty2array'=>[],
);

echo json_encode($foo);  // {"empty2object":{},"empty2array":[]}

?>

down

Istratov Vadim ¶

15 years ago


Be careful with floating values in some locales (e.g. russian) with comma (",") as decimal point. Code:



<?php

setlocale(LC_ALL, 'ru_RU.utf8');



$arr = array('element' => 12.34);

echo json_encode( $arr );

?>



Output will be:

--------------

{"element":12,34}

--------------



Which is NOT a valid JSON markup. You should convert floating point variable to strings or set locale to something like "LC_NUMERIC, 'en_US.utf8'" before using json_encode.

down

ck at ergovia dot de ¶

11 years ago


Attention when passing a plain array to json_encode and using JSON_FORCE_OBJECT. It figured out that the index-order of the resulting JSON-string depends on the system PHP is running on.

$a = array("a" , "b", "c");
echo json_encode($a, JSON_FORCE_OBJECT);

On Xampp (Windows) you get:

{"0":"a","1":"b","2":"c"}';

On a machine running debian I get:

{"2":"a","1":"b","0":"c"}';

Note that the key:value pairs are different!

Solution here was to use array_combine to create a ssociative array and then pass it to json_encode:

json_encode(array_combine(range(0, count($a) - 1), $a), JSON_FORCE_OBJECT);

down

ryan at ryanparman dot com ¶

14 years ago


I came across the "bug" where running json_encode() over a SimpleXML object was ignoring the CDATA. I ran across http://bugs.php.net/42001 and http://bugs.php.net/41976, and while I agree with the poster that the documentation should clarify gotchas like this, I was able to figure out how to workaround it.

You need to convert the SimpleXML object back into an XML string, then re-import it back into SimpleXML using the LIBXML_NOCDATA option. Once you do this, then you can use json_encode() and still get back the CDATA.

<?php
// Pretend we already have a complex SimpleXML object stored in $xml
$json = json_encode(new SimpleXMLElement($xml->asXML(), LIBXML_NOCDATA));
?>

down

guilhenfsu at gmail dot com ¶

11 years ago


Solution for UTF-8 Special Chars.

<?

$array = array('nome'=>'Paição','cidade'=>'São Paulo');

$array = array_map('htmlentities',$array);

//encode
$json = html_entity_decode(json_encode($array));

//Output: {"nome":"Paição","cidade":"São Paulo"}
echo $json;

?>

down

Walter Tross ¶

9 years ago


If you need pretty-printed output, but want it indented by 2 spaces instead of 4:

$json_indented_by_4 = json_encode($output, JSON_UNESCAPED_SLASHES|JSON_PRETTY_PRINT);
$json_indented_by_2 = preg_replace('/^(  +?)\\1(?=[^ ])/m', '$1', $json_indented_by_4);

down

Garrett ¶

16 years ago


A note about json_encode automatically quoting numbers:

It appears that the json_encode function pays attention to the data type of the value. Let me explain what we came across:

We have found that when retrieving data from our database, there are occasions when numbers appear as strings to json_encode which results in double quotes around the values.

This can lead to problems within javascript functions expecting the values to be numeric.

This was discovered when were were retrieving fields from the database which contained serialized arrays. After unserializing them and sending them through the json_encode function the numeric values in the original array were now being treated as strings and showing up with double quotes around them.

The fix: Prior to encoding the array, send it to a function which checks for numeric types and casts accordingly. Encoding from then on worked as expected.

down

Sam Barnum ¶

15 years ago


Note that if you try to encode an array containing non-utf values, you'll get null values in the resulting JSON string.  You can batch-encode all the elements of an array with the array_map function:
<?php
$encodedArray = array_map(utf8_encode, $rawArray);
?>

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