预定义常量

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() 函数,或 JsonException 类中的 code 变量所返回的错误类型。

JSON_ERROR_NONE (int)
没有错误发生。
JSON_ERROR_DEPTH (int)
到达了最大堆栈深度。
JSON_ERROR_STATE_MISMATCH (int)
出现了下溢(underflow)或者模式不匹配。
JSON_ERROR_CTRL_CHAR (int)
控制字符错误,可能是编码不对。
JSON_ERROR_SYNTAX (int)
语法错误。
JSON_ERROR_UTF8 (int)
异常的 UTF-8 字符,也许是因为不正确的编码。
JSON_ERROR_RECURSION (int)
传递给 json_encode() 函数的对象或数组包含了递归引用,导致无法被编码。如果打开了 JSON_PARTIAL_OUTPUT_ON_ERROR 选项,则牵涉到递归引用的数据会转换成 null 后返回。
JSON_ERROR_INF_OR_NAN (int)
传递给 json_encode() 函数的参数中包含了 NANINF,导致编码出错。如果打开了 JSON_PARTIAL_OUTPUT_ON_ERROR 选项,则牵涉到对应不可编码的数字,会转换成数字 0 后返回。
JSON_ERROR_UNSUPPORTED_TYPE (int)
传递了不支持的数据类型给 json_encode() 函数,比如 资源(resource)。如果打开了 JSON_PARTIAL_OUTPUT_ON_ERROR 选项,则对于不支持的数据类型,会转换成 null 后返回。
JSON_ERROR_INVALID_PROPERTY_NAME (int)
A key starting with \u0000 character was in the string passed to json_decode() when decoding a JSON object into a PHP object.
JSON_ERROR_UTF16 (int)
Single unpaired UTF-16 surrogate in unicode escape contained in the JSON string passed to json_encode().

下面的常量可以和 json_decode() 的 form 选项结合使用。

JSON_BIGINT_AS_STRING (int)
将大数字编码成原始字符原来的值。
JSON_OBJECT_AS_ARRAY (int)
将 JSON 对象作为数组解码。当调用 json_decode() 且第二个参数为 true 时此选项会自动添加。

下面的常量可以和 json_encode() 的 form 选项结合使用。

JSON_HEX_TAG (int)
所有的 < 和 > 转换成 \u003C 和 \u003E。
JSON_HEX_AMP (int)
所有的 & 转换成 \u0026。
JSON_HEX_APOS (int)
所有的 ' 转换成 \u0027。
JSON_HEX_QUOT (int)
所有的 " 转换成 \u0022。
JSON_FORCE_OBJECT (int)
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。
JSON_NUMERIC_CHECK (int)
将所有数字字符串编码成数字(numbers)。
JSON_PRETTY_PRINT (int)
用空白字符格式化返回的数据。
JSON_UNESCAPED_SLASHES (int)
不要编码 /
JSON_UNESCAPED_UNICODE (int)
以字面编码多字节 Unicode 字符(默认是编码成 \uXXXX)。
JSON_PARTIAL_OUTPUT_ON_ERROR (int)
Substitute some unencodable values instead of failing.
JSON_PRESERVE_ZERO_FRACTION (int)
确保 float 值始终编码为为 float 值。
JSON_UNESCAPED_LINE_TERMINATORS (int)
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.

下面的常量可以和 json_decode()json_encode() 的 form 选项结合使用。

JSON_INVALID_UTF8_IGNORE (int)
忽略无效的 UTF-8 字符。自 PHP 7.2.0 起生效。
JSON_INVALID_UTF8_SUBSTITUTE (int)
将无效 UTF-8 字符转换为 \0xfffd(Unicode 字符“虚缺号”)。自 PHP 7.2.0 起生效。
JSON_THROW_ON_ERROR (int)
如果发生错误则会抛出 JsonException,而不是通过 json_last_error()json_last_error_msg() 检索设置到全局的错误状态。JSON_PARTIAL_OUTPUT_ON_ERROR 优先于 JSON_THROW_ON_ERROR。自 PHP 7.3.0 起生效。
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User Contributed Notes 7 notes

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61
majid4466 at gmail dot com
6 years ago
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);
$good  = json_encode($arrayJSON_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]
?>
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62
Yzmir Ramirez
8 years ago
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 => 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_ERROR_DEPTH => 1
JSON_ERROR_STATE_MISMATCH => 2
JSON_ERROR_CTRL_CHAR => 3

JSON_ERROR_SYNTAX => 4

JSON_ERROR_UTF8 => 5
JSON_OBJECT_AS_ARRAY => 1

JSON_BIGINT_AS_STRING => 2
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6
ASchmidt at Anamera dot net
4 years ago
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.
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6
Anonymous
4 years ago
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
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4
JuanP
7 years ago
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
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-26
on5wis at mac dot com
7 years ago
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
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-56
Anonymous
7 years ago
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"}
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