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 NAN 或 INF，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 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): 用不可编码的值来代替失败。
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() 及 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() 和 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。
JSON_ERROR_NON_BACKED_ENUM (int): 传递给 json_encode() 的值包含了无法序列化的非支持的枚举。自 PHP 8.1.0 起生效。

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用户贡献的备注 6 notes

down

majid4466 at gmail dot com ¶

8 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); 
$good  = json_encode($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]
?>

down

Yzmir Ramirez ¶

10 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

down

nikospapoutsis ¶

2 years 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 $case2 = json_encode($array,  JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES );
echo $case3 = json_encode($array,  JSON_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.

down

ASchmidt at Anamera dot net ¶

6 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.

down

eduard dot amoros dot wahl at gmail dot com ¶

3 months ago

Warning about JSON_NUMERIC_CHECK and scientific notation.

JSON_NUMERIC_CHECK will remove scientific notation. Thus,
json_encode(['scientificNumber' => '1e-4'], JSON_NUMERIC_CHECK);
will return {"scientificNumber":0.0001}

You have to account for this, as it may defeat the whole purpose of scientific notation.

down

-3

Anonymous ¶

6 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