json函数（JavaScript对象符号）

下列常量由此扩展定义，且仅在此扩展编译入 PHP 或在运行时动态载入时可用。

以下常量表示了`json_last_error()`所返回的错误类型。

JSON_ERROR_NONE(integer)没有错误发生。自 PHP 5.3.0 起生效。
JSON_ERROR_DEPTH(integer)到达了最大堆栈深度。自 PHP 5.3.0 起生效。
JSON_ERROR_STATE_MISMATCH(integer)出现了下溢（underflow）或者模式不匹配。自 PHP 5.3.0 起生效。
JSON_ERROR_CTRL_CHAR(integer)控制字符错误，可能是编码不对。自 PHP 5.3.0 起生效。
JSON_ERROR_SYNTAX(integer)语法错误。自 PHP 5.3.0 起生效。
JSON_ERROR_UTF8(integer)异常的 UTF-8 字符，也许是因为不正确的编码。自 PHP 5.3.3 起生效。
JSON_ERROR_RECURSION(integer) The object or array passed to json_encode() include recursive references and cannot be encoded. If the JSON_PARTIAL_OUTPUT_ON_ERROR option was given, NULL will be encoded in the place of the recursive reference. Available since PHP 5.5.0.
JSON_ERROR_INF_OR_NAN(integer) The value passed to json_encode() includes either NAN or INF. If the JSON_PARTIAL_OUTPUT_ON_ERROR option was given,0will be encoded in the place of these special numbers. Available since PHP 5.5.0.
JSON_ERROR_UNSUPPORTED_TYPE(integer) A value of an unsupported type was given to json_encode(), such as a resource. If the JSON_PARTIAL_OUTPUT_ON_ERROR option was given, NULL will be encoded in the place of the unsupported value. Available since PHP 5.5.0.
JSON_ERROR_INVALID_PROPERTY_NAME(integer)A key starting with \u0000 character was in the string passed to json_decode() when decoding a JSON object into a PHP object. Available since PHP 7.0.0.
JSON_ERROR_UTF16(integer)Single unpaired UTF-16 surrogate in unicode escape contained in the JSON string passed to json_encode(). Available since PHP 7.0.0.

下面的常量可以和 json_decode() 的 form 选项结合使用。

JSON_BIGINT_AS_STRING(integer)将大数字编码成原始字符原来的值。自 PHP 5.4.0 起生效。

JSON_OBJECT_AS_ARRAY(integer) Decodes JSON objects as PHP array. This option can be added automatically by calling json_decode() with the second parameter equal to TRUE. Available since PHP 5.4.0.

下面的常量可以和`json_encode()`的 form 选项结合使用。

JSON_HEX_TAG(integer)所有的 < 和 > 转换成 \u003C 和 \u003E。自 PHP 5.3.0 起生效。
JSON_HEX_AMP(integer)所有的 & 转换成 \u0026。自 PHP 5.3.0 起生效。
JSON_HEX_APOS(integer)所有的 ' 转换成 \u0027。自 PHP 5.3.0 起生效。
JSON_HEX_QUOT(integer)所有的 " 转换成 \u0022。自 PHP 5.3.0 起生效。
JSON_FORCE_OBJECT(integer)使一个非关联数组输出一个类（Object）而非数组。在数组为空而接受者需要一个类（Object）的时候尤其有用。自 PHP 5.3.0 起生效。
JSON_NUMERIC_CHECK(integer)将所有数字字符串编码成数字（numbers）。自 PHP 5.3.3 起生效。
JSON_PRETTY_PRINT(integer)用空白字符格式化返回的数据。自 PHP 5.4.0 起生效。
JSON_UNESCAPED_SLASHES(integer) 不要编码/。自 PHP 5.4.0 起生效。
JSON_UNESCAPED_UNICODE(integer)以字面编码多字节 Unicode 字符（默认是编码成 \uXXXX）。自 PHP 5.4.0 起生效。
JSON_PARTIAL_OUTPUT_ON_ERROR(integer)Substitute some unencodable values instead of failing. Available since PHP 5.5.0.
JSON_PRESERVE_ZERO_FRACTION(integer)Ensures that float values are always encoded as a float value. Available since PHP 5.6.6.
JSON_UNESCAPED_LINE_TERMINATORS(integer) The line terminators are kept unescaped when JSON_UNESCAPED_UNICODE is supplied. It uses the same behaviour as it was before PHP 7.1 without this constant. Available since PHP 7.1.0.

To get a really clean json string use these three constants like so:
<?php
$array = ['€', 'http://example.com/some/cool/page', '337'];
$bad  = json_encode($array); 
$good = json_encode($array, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES | JSON_NUMERIC_CHECK);
// $bad would be ["\u20ac","http:\/\/example.com\/some\/cool\/page","337"]
// $good would be ["€","http://example.com/some/cool/page",337]
?>

If you curious of the numeric values of the constants, as of JSON 1.2.1, the constants have the following values (not that you should use the numbers directly):JSON_HEX_TAG => 1JSON_HEX_AMP => 2JSON_HEX_APOS => 4JSON_HEX_QUOT => 8JSON_FORCE_OBJECT => 16JSON_NUMERIC_CHECK => 32JSON_UNESCAPED_SLASHES => 64JSON_PRETTY_PRINT => 128JSON_UNESCAPED_UNICODE => 256JSON_ERROR_DEPTH => 1JSON_ERROR_STATE_MISMATCH => 2JSON_ERROR_CTRL_CHAR => 3JSON_ERROR_SYNTAX => 4JSON_ERROR_UTF8 => 5JSON_OBJECT_AS_ARRAY => 1JSON_BIGINT_AS_STRING => 2

In a multi-level array, JSON_FORCE_OBJECT will encode ALL nested numeric arrays as objects. 
If your concern was ONLY the first-level array (e.g., to make it suitable as a MySQL JSON column), you could just cast your first-level array to object, e.g.:
<?php
$json = json_encode( (object) $array, JSON_PRESERVE_ZERO_FRACTION+JSON_UNESCAPED_UNICODE );
?>
Or, if you have large arrays and are concerned about the overhead of object casting, you could append a "null" value beyond the size of the array, which will force the array to become associative:
<?php
$beyond = count( $array ) + 1;
if ( !array_key_exists( $beyond, $array) )
   $array[ $beyond ] = NULL;
$json = json_encode( $array, JSON_PRESERVE_ZERO_FRACTION+JSON_UNESCAPED_UNICODE );
?>
Of course, your later code has to treat an element with a "NULL" value the same as "!isset()", if it iterates the array.

flags JSON_NUMERIC_CHECK and JSON_PRESERVE_ZERO_FRACTION are broken in php 7+ — json_encode((float)8.8) returns "8.8000000000000007", and json_encode((float)8.8, JSON_NUMERIC_CHECK) and json_encode((float)8.8, JSON_PRESERVE_ZERO_FRACTION) return "8.8000000000000007" too.the only way to fix this is setting "serialize_precision = -1" in php.ini

Updated format values list:
  JSON_HEX_TAG => 1
  JSON_HEX_AMP => 2
  JSON_HEX_APOS => 4
  JSON_HEX_QUOT => 8
  JSON_FORCE_OBJECT => 16
  JSON_NUMERIC_CHECK => 32
  JSON_UNESCAPED_SLASHES => 64
  JSON_PRETTY_PRINT => 128
  JSON_UNESCAPED_UNICODE => 256
  JSON_PARTIAL_OUTPUT_ON_ERROR => 512
  JSON_PRESERVE_ZERO_FRACTION => 1024

since json_encode expects a UTF-8 string there is no need to encode the € symbol.I suggest you try to echo : json_encode('€');It gives: "\u20ac"I'm running PHP 5.6.5 on the CLI, on MacOS X 10.10

I am working with "Marathi Language Data" and I found that when I encoded Marathi data to json using json_encode it returned me unicode values of each character like below:
Program : 
<?php
$ar = array("word" => "धाडस");
echo json_encode($ar);
?>
Output of program is : 
{"word":"\u0927\u093e\u0921\u0938"}
This is not expected output because what I need is output as
{"word":"धाडस"}
So I used following code:
<?php
$ar = array("word" => "धाडस");
echo json_encode($ar, JSON_UNESCAPED_UNICODE);
?>
And I got the required output as :
{"word":"धाडस"}

json函数（JavaScript对象符号）

以下常量表示了json_last_error()所返回的错误类型。

下面的常量可以和json_encode()的 form 选项结合使用。

以下常量表示了`json_last_error()`所返回的错误类型。

下面的常量可以和`json_encode()`的 form 选项结合使用。