目前，JSON已经成为最流行的数据交换格式之一，各大网站的API几乎都支持它。
我写过一篇《数据类型和JSON格式》，探讨它的设计思想。今天，我想总结一下PHP语言对它的支持，这是开发互联网应用程序（特别是编写API）必须了解的知识。
从5.2版本开始，PHP原生提供json_encode()和json_decode()函数，前者用于编码，后者用于解码。
一、json_encode()
该函数主要用来将数组和对象，转换为json格式。先看一个数组转换的例子：
$arr = array ('a'=>1,'b'=>2,'c'=>3,'d'=>4,'e'=>5);echo json_encode($arr);结果为
{"a":1,"b":2,"c":3,"d":4,"e":5}
再看一个对象转换的例子：
$obj->body = 'another post';$obj->id = 21;$obj->approved = true;$obj->favorite_count = 1;$obj->status = NULL;echo json_encode($obj);
结果为
{ "body":"another post", "id":21, "approved":true, "favorite_count":1, "status":null}由于json只接受utf-8编码的字符，所以json_encode()的参数必须是utf-8编码，否则会得到空字符或者null。当中文使用GB2312编码，或者外文使用ISO-8859-1编码的时候，这一点要特别注意。
二、索引数组和关联数组
PHP支持两种数组，一种是只保存"值"（value）的索引数组（indexed array），另一种是保存"名值对"（name/value）的关联数组（associative array）。
由于javascript不支持关联数组，所以json_encode()只将索引数组（indexed array）转为数组格式，而将关联数组（associative array）转为对象格式。
比如，现在有一个索引数组
$arr = Array('one', 'two', 'three');echo json_encode($arr);结果为：
["one","two","three"]
如果将它改为关联数组：
$arr = Array('1'=>'one', '2'=>'two', '3'=>'three');echo json_encode($arr);结果就变了：
{"1":"one","2":"two","3":"three"}注意，数据格式从"[]"（数组）变成了"{}"（对象）。
如果你需要将"索引数组"强制转化成"对象"，可以这样写
json_encode( (object)$arr );
或者
json_encode ( $arr, JSON_FORCE_OBJECT );
三、类（class）的转换
下面是一个PHP的类：
class Foo { const ERROR_CODE = '404'; public $public_ex = 'this is public'; private $private_ex = 'this is private!'; protected $protected_ex = 'this should be protected'; public function getErrorCode() { return self::ERROR_CODE; }}现在，对这个类的实例进行json转换：
$foo = new Foo;$foo_json = json_encode($foo);echo $foo_json;
输出结果是
{"public_ex":"this is public"}
可以看到，除了公开变量（public），其他东西（常量、私有变量、方法等等）都遗失了。
四、json_decode()
该函数用于将json文本转换为相应的PHP数据结构。下面是一个例子：
$json = '{"foo": 12345}'; $obj = json_decode($json); print $obj->{'foo'}; // 12345通常情况下，json_decode()总是返回一个PHP对象，而不是数组。比如：
$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}'; var_dump(json_decode($json));结果就是生成一个PHP对象：
object(stdClass)#1 (5) { ["a"] => int(1) ["b"] => int(2) ["c"] => int(3) ["d"] => int(4) ["e"] => int(5) }如果想要强制生成PHP关联数组，json_decode()需要加一个参数true：
$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';var_dump(json_decode($json,true));结果就生成了一个关联数组：
array(5) { ["a"] => int(1) ["b"] => int(2) ["c"] => int(3) ["d"] => int(4) ["e"] => int(5) } 五、json_decode()的常见错误
下面三种json写法都是错的，你能看出错在哪里吗？
$bad_json = "{ 'bar': 'baz' }";$bad_json = '{ bar: "baz" }'; $bad_json = '{ "bar": "baz", }';对这三个字符串执行json_decode()都将返回null，并且报错。
第一个的错误是，json的分隔符（delimiter）只允许使用双引号，不能使用单引号。第二个的错误是，json名值对的"名"（冒号左边的部分），任何情况下都必须使用双引号。第三个的错误是，最后一个值之后不能添加逗号（trailing comma）。
另外，json只能用来表示对象（object）和数组（array），如果对一个字符串或数值使用json_decode()，将会返回null。
var_dump(json_decode("Hello World")); //null下面给大家介绍哦php语言的json实现
由于开发一个ajax file manager for web开源项目,数据交换使用的json格式，后来发现在低版本的php上运行会有问题，仔细调试发现json_decode和json_encode无法正常工作，于是查阅资料，发现低版本的php没有实现这两个函数，为了兼容性，我只好自己实现一个php版的json编码解码代码，并保证和json2.js的一致，测试调试并通过，现在将其公布出来，供有相同需求的同学使用：
<?php /* * **************************************************************************** * $base: $ * * $Author: $ * Berlin Qin * * $History: base.js $ * Berlin Qin // created * * $contacted * webfmt@gmail.com * www.webfmt.com * * *************************************************************************** */ /* =========================================================================== * license * * 、Open Source Licenses * webfmt is distributed under the GPL, LGPL and MPL open source licenses. * This triple copyleft licensing model avoids incompatibility with other open source licenses. * These Open Source licenses are specially indicated for: * Integrating webfmt into Open Source software; * Personal and educational use of webfmt; * Integrating webfmt in commercial software, * taking care of satisfying the Open Source licenses terms, * while not able or interested on supporting webfmt and its development. * * 、Commercial License fbis source Closed Distribution License - CDL * For many companies and products, Open Source licenses are not an option. * This is why the fbis source Closed Distribution License (CDL) has been introduced. * It is a non-copyleft license which gives companies complete freedom * when integrating webfmt into their products and web sites. * This license offers a very flexible way to integrate webfmt in your commercial application. * These are the main advantages it offers over an Open Source license: * Modifications and enhancements doesn't need to be released under an Open Source license; * There is no need to distribute any Open Source license terms alongside with your product * and no reference to it have to be done; * No references to webfmt have to be done in any file distributed with your product; * The source code of webfmt doesn't have to be distributed alongside with your product; * You can remove any file from webfmt when integrating it with your product. * The CDL is a lifetime license valid for all releases of webfmt published during * and before the year following its purchase. * It's valid for webfmt releases also. It includes year of personal e-mail support. * * ************************************************************************************************************************************************* */ function jsonDecode($json) { $result = array(); try { if (PHP_VERSION_ID > ) { $result = (array) json_decode($json); } else { $json = str_replace(array("////", "///""), array("&#;", "&#;"), $json); $parts = preg_split("@(/"[^/"]*/")|([/[/]/{/},:])|/s@is", $json, -, PREG_SPLIT_NO_EMPTY | PREG_SPLIT_DELIM_CAPTURE); foreach ($parts as $index => $part) { if (strlen($part) == ) { switch ($part) { case "[": case "{": $parts[$index] = "array("; break; case "]": case "}": $parts[$index] = ")"; break; case ":": $parts[$index] = "=>"; break; case ",": break; default: break; } } } $json = str_replace(array("&#;", "&#;", "$"), array("////", "///"", "//$"), implode("", $parts)); $result = eval("return $json;"); } } catch (Exception $e) { $result = array("error" => $e->getCode()); } return $result; } function valueTostr($val) { if (is_string($val)) { $val = str_replace('/"', "///"", $val); $val = str_replace("//", "////", $val); $val = str_replace("/", "///", $val); $val = str_replace("/t", "//t", $val); $val = str_replace("/n", "//n", $val); $val = str_replace("/r", "//r", $val); $val = str_replace("/b", "//b", $val); $val = str_replace("/f", "//f", $val); return '"' . $val . '"'; } elseif (is_int($val)) return sprintf('%d', $val); elseif (is_float($val)) return sprintf('%F', $val); elseif (is_bool($val)) return ($val ? 'true' : 'false'); else return 'null'; } function jsonEncode($arr) { $result = "{}"; try { if (PHP_VERSION_ID > ) { $result = json_encode($arr); } else { $parts = array(); $is_list = false; if (!is_array($arr)) { $arr = (array) $arr; } $end = count($arr) - ; if (count($arr) > ) { if (is_numeric(key($arr))) { $result = "["; for ($i = ; $i < count($arr); $i++) { if (is_array($arr[$i])) { $result = $result . jsonEncode($arr[$i]); } else { $result = $result . valueTostr($arr[$i]); } if ($i != $end) { $result = $result . ","; } } $result = $result . "]"; } else { $result = "{"; $i = ; foreach ($arr as $key => $value) { $result = $result . '"' . $key . '":'; if (is_array($value)) { $result = $result . jsonEncode($value); } else { $result = $result . valueTostr($value); } if ($i != $end) { $result = $result . ","; } $i++; } $result = $result . "}"; } } else { $result = "[]"; } } } catch (Exception $e) { } return $result; } ?> 如果使用过程有什么问题，可以给我email.欢迎大家指出错误！