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。自 PHP 5.3.0 起生效。
JSON_ERROR_DEPTH (int)
到达了最大堆栈深度。自 PHP 5.3.0 起生效。
JSON_ERROR_STATE_MISMATCH (int)
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 (int)
控制字符错误,可能是编码不对。自 PHP 5.3.0 起生效。
JSON_ERROR_SYNTAX (int)
语法错误。自 PHP 5.3.0 起生效。
JSON_ERROR_UTF8 (int)
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 (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。自 PHP 5.5.0 起生效。
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。自 PHP 5.5.0 起生效。
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。自 PHP 5.5.0 起生效。
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. Available since PHP 7.0.0.
JSON_ERROR_UTF16 (int)
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 (int)
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 (int)
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 (int)
所有的 < 和 > 转换成 \u003C 和 \u003E。 自 PHP 5.3.0 起生效。
JSON_HEX_AMP (int)
所有的 & 转换成 \u0026。 自 PHP 5.3.0 起生效。
JSON_HEX_APOS (int)
所有的 ' 转换成 \u0027。 自 PHP 5.3.0 起生效。
JSON_HEX_QUOT (int)
所有的 " 转换成 \u0022。 自 PHP 5.3.0 起生效。
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。 自 PHP 5.3.0 起生效。
JSON_NUMERIC_CHECK (int)
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 (int)
用空白字符格式化返回的数据。 自 PHP 5.4.0 起生效。
JSON_UNESCAPED_SLASHES (int)
不要编码 /。 自 PHP 5.4.0 起生效。
JSON_UNESCAPED_UNICODE (int)
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 (int)
Substitute some unencodable values instead of failing. Available since PHP 5.5.0.
JSON_PRESERVE_ZERO_FRACTION (int)
Ensures that float values are always encoded as a float value. Available since PHP 5.6.6.
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)
Ignore invalid UTF-8 characters. Available as of PHP 7.2.0.
JSON_INVALID_UTF8_SUBSTITUTE (int)
Convert invalid UTF-8 characters to \0xfffd (Unicode Character 'REPLACEMENT CHARACTER') Available as of PHP 7.2.0.
JSON_THROW_ON_ERROR (int)
Throws JsonException if an error occurs instead of setting the global error state that is retrieved with json_last_error() and json_last_error_msg(). JSON_PARTIAL_OUTPUT_ON_ERROR takes precedence over JSON_THROW_ON_ERROR. Available as of PHP 7.3.0.
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User Contributed Notes 7 notes

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70
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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58
Yzmir Ramirez
7 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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8
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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1
nikospapoutsis
10 days ago
Be EXTREMELY cautious when using the code majid4466 at gmail dot com provided, or JSON_NUMERIC_CHECK in general.

For example, in php 7.4 and 8.1 with precision: 14 and serialize_precision: -1 we get:

<?php
$array
= ['€', 55.6666666666666666, 'http://example.com/some/cool/page', '000337', '55.6666666666666666'];
echo
$case1 = json_encode($array);
echo
$case2 = json_encode($arrayJSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES );
echo
$case3 = json_encode($arrayJSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES | JSON_NUMERIC_CHECK);

[
"\u20ac",55.666666666666664,"http:\/\/example.com\/some\/cool\/page","000337","55.6666666666666666"]
// in $case1, both euro sign and the url change but we also lost a digit in our unquoted float (due to precision)

["€",55.666666666666664,"http://example.com/some/cool/page","000337","55.6666666666666666"]
// in $case2, both euro sign and the url stay exactly the same but we still lost a digit in our unquoted float (due to precision)

["€",55.666666666666664,"http://example.com/some/cool/page",337,55.666666666666664]
// in $case3, we once again keep euro sign and the url intact but this time not only our unquoted float lost a digit
// but the same happened to our quoted float and the number/string lost its leading zeros too

Also, note that in php 5.x you will probably get some different but equally wrong results as default values may be different and some functions have changed internally as well.
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0
JuanP
6 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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-3
Anonymous
3 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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-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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