php中json

一、json_encode() 该函数主要用来将数组和对象，转换为json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

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：

<code>
　　<span>$arr</span> <span>=</span> <span>array</span> <span>(</span><span>'a'</span><span>=</span><span>&gt;</span><span>1</span><span>,</span><span>'b'</span><span>=</span><span>&gt;</span><span>2</span><span>,</span><span>'c'</span><span>=</span><span>&gt;</span><span>3</span><span>,</span><span>'d'</span><span>=</span><span>&gt;</span><span>4</span><span>,</span><span>'e'</span><span>=</span><span>&gt;</span><span>5</span><span>)</span><span>;</span>
　　
　　<span>echo</span> <span>json_encode<span>(</span></span><span>$arr</span><span>)</span><span>;</span>
　　
</code>

结果为

<code>
　　<span>{</span><span>"a"</span><span>:</span><span>1</span><span>,</span><span>"b"</span><span>:</span><span>2</span><span>,</span><span>"c"</span><span>:</span><span>3</span><span>,</span><span>"d"</span><span>:</span><span>4</span><span>,</span><span>"e"</span><span>:</span><span>5</span><span>}</span>
　　
</code>

再看一个对象转换的例子：

<code>
　　<span>$obj</span><span>-</span><span>&gt;</span><span>body</span>           <span>=</span> <span>'another post'</span><span>;</span>
　　
　　<span>$obj</span><span>-</span><span>&gt;</span><span>id</span>             <span>=</span> <span>21</span><span>;</span>
　　
　　<span>$obj</span><span>-</span><span>&gt;</span><span>approved</span>       <span>=</span> <span>true</span><span>;</span>
　　
　　<span>$obj</span><span>-</span><span>&gt;</span><span>favorite_count</span> <span>=</span> <span>1</span><span>;</span>
　　
　　<span>$obj</span><span>-</span><span>&gt;</span><span>status</span>         <span>=</span> <span>NULL</span><span>;</span>
　　
　　<span>echo</span> <span>json_encode<span>(</span></span><span>$obj</span><span>)</span><span>;</span>
　　
</code>

结果为

<code>
　　<span>{</span>
　　　　<span>"body"</span><span>:</span><span>"another post"</span><span>,</span>
　　
　　　　<span>"id"</span><span>:</span><span>21</span><span>,</span>
　　
　　　　<span>"approved"</span><span>:</span><span>true</span><span>,</span>
　　
　　　　<span>"favorite_count"</span><span>:</span><span>1</span><span>,</span>
　　
　　　　<span>"status"</span><span>:</span><span>null</span>
　　<span>}</span> 
　　
</code>

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

<code>
　　<span>$arr</span> <span>=</span> <span>Array</span><span>(</span><span>'one'</span><span>,</span> <span>'two'</span><span>,</span> <span>'three'</span><span>)</span><span>;</span>
　　
　　<span>echo</span> <span>json_encode<span>(</span></span><span>$arr</span><span>)</span><span>;</span>
　　
</code>

结果为：

<code>
　　<span>[</span><span>"one"</span><span>,</span><span>"two"</span><span>,</span><span>"three"</span><span>]</span> 
　　
</code>

如果将它改为关联数组：

<code>
　　<span>$arr</span> <span>=</span> <span>Array</span><span>(</span><span>'1'</span><span>=</span><span>&gt;</span><span>'one'</span><span>,</span> <span>'2'</span><span>=</span><span>&gt;</span><span>'two'</span><span>,</span> <span>'3'</span><span>=</span><span>&gt;</span><span>'three'</span><span>)</span><span>;</span>
 　　
　　<span>echo</span> <span>json_encode<span>(</span></span><span>$arr</span><span>)</span><span>;</span>
　　　　
</code>

结果就变了：

<code>
　　<span>{</span><span>"1"</span><span>:</span><span>"one"</span><span>,</span><span>"2"</span><span>:</span><span>"two"</span><span>,</span><span>"3"</span><span>:</span><span>"three"</span><span>}</span> 
　　
</code>

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

<code>
　　<span>json_encode<span>(</span></span> <span>(</span>object<span>)</span><span>$arr</span> <span>)</span><span>;</span>
　　
</code>

或者

<code>
　　json_encode <span>(</span> <span>$arr</span><span>,</span> <span>JSON_FORCE_OBJECT</span> <span>)</span><span>;</span>
　　
</code>

三、类（class）的转换

下面是一个PHP的类：

<code>
　　<span>class</span> <span>Foo</span> <span>{</span>
　　
　　　　<span>const</span>     <span>ERROR_CODE</span> <span>=</span> <span>'404'</span><span>;</span>
　　
　　　　<span>public</span>    <span>$public_ex</span> <span>=</span> <span>'this is public'</span><span>;</span>
　　
　　　　<span>private</span>   <span>$private_ex</span> <span>=</span> <span>'this is private!'</span><span>;</span>
　　
　　　　<span>protected</span> <span>$protected_ex</span> <span>=</span> <span>'this should be protected'</span><span>;</span> 
 　　
　　　　<span>public</span> <span>function</span> <span>getErrorCode<span>(</span></span><span>)</span> <span>{</span>
　　
　　　　　　<span>return</span> self<span>:</span><span>:</span><span>ERROR_CODE</span><span>;</span>
　　
　　　　<span>}</span>
　　
　　<span>}</span>
　　
</code>

现在，对这个类的实例进行json转换：

<code>
　　<span>$foo</span> <span>=</span> <span>new</span> <span>Foo</span><span>;</span>
　　
　　<span>$foo_json</span> <span>=</span> <span>json_encode<span>(</span></span><span>$foo</span><span>)</span><span>;</span>
　　
　　<span>echo</span> <span>$foo_json</span><span>;</span>
　　
</code>

输出结果是

<code>
　　<span>{</span><span>"public_ex"</span><span>:</span><span>"this is public"</span><span>}</span> 
　　
</code>

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：

<code>
　　<span>$json</span> <span>=</span> <span>'{"foo": 12345}'</span><span>;</span>
 　　
　　<span>$obj</span> <span>=</span> <span>json_decode<span>(</span></span><span>$json</span><span>)</span><span>;</span>
　　
　　<span>print</span> <span>$obj</span><span>-</span><span>&gt;</span><span>{</span><span>'foo'</span><span>}</span><span>;</span><span> // 12345
</span>　　
</code>

通常情况下，json_decode()总是返回一个PHP对象，而不是数组。比如：

<code>
　　<span>$json</span> <span>=</span> <span>'{"a":1,"b":2,"c":3,"d":4,"e":5}'</span><span>;</span>
 　　
　　<span>var_dump<span>(</span></span><span>json_decode<span>(</span></span><span>$json</span><span>)</span><span>)</span><span>;</span>
　　
</code>

结果就是生成一个PHP对象：

<code>
　　<span>object<span>(</span></span>stdClass<span>)</span>#<span>1</span> <span>(</span><span>5</span><span>)</span> <span>{</span>
　　
　　　　<span>[</span><span>"a"</span><span>]</span> <span>=</span><span>&gt;</span> <span>int<span>(</span></span><span>1</span><span>)</span>
　　　　<span>[</span><span>"b"</span><span>]</span> <span>=</span><span>&gt;</span> <span>int<span>(</span></span><span>2</span><span>)</span>
　　　　<span>[</span><span>"c"</span><span>]</span> <span>=</span><span>&gt;</span> <span>int<span>(</span></span><span>3</span><span>)</span>
　　　　<span>[</span><span>"d"</span><span>]</span> <span>=</span><span>&gt;</span> <span>int<span>(</span></span><span>4</span><span>)</span>
　　　　<span>[</span><span>"e"</span><span>]</span> <span>=</span><span>&gt;</span> <span>int<span>(</span></span><span>5</span><span>)</span>
　　
　　<span>}</span>
　　
</code>

如果想要强制生成PHP关联数组，json_decode()需要加一个参数true：

<code>
　　<span>$json</span> <span>=</span> <span>'{"a":1,"b":2,"c":3,"d":4,"e":5}'</span><span>;</span>
 　　
　　<span>var_dump<span>(</span></span><span>json_decode<span>(</span></span><span>$json</span><span>,</span><span>true</span><span>)</span><span>)</span><span>;</span>
　　
</code>

结果就生成了一个关联数组：

<code>
　　<span>array</span><span>(</span><span>5</span><span>)</span> <span>{</span>
　　
　　 　　<span>[</span><span>"a"</span><span>]</span> <span>=</span><span>&gt;</span> <span>int<span>(</span></span><span>1</span><span>)</span>
　　 　　<span>[</span><span>"b"</span><span>]</span> <span>=</span><span>&gt;</span> <span>int<span>(</span></span><span>2</span><span>)</span>
　　 　　<span>[</span><span>"c"</span><span>]</span> <span>=</span><span>&gt;</span> <span>int<span>(</span></span><span>3</span><span>)</span>
　　 　　<span>[</span><span>"d"</span><span>]</span> <span>=</span><span>&gt;</span> <span>int<span>(</span></span><span>4</span><span>)</span>
　　 　　<span>[</span><span>"e"</span><span>]</span> <span>=</span><span>&gt;</span> <span>int<span>(</span></span><span>5</span><span>)</span>
　　
　　<span>}</span>
　　
</code>

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？

<code>
　　<span>$bad_json</span> <span>=</span> <span>"{ 'bar': 'baz' }"</span><span>;</span>
　　
　　<span>$bad_json</span> <span>=</span> <span>'{ bar: "baz" }'</span><span>;</span>
　　
　　<span>$bad_json</span> <span>=</span> <span>'{ "bar": "baz", }'</span><span>;</span>
　　
</code>

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。

<code>
　　<span>var_dump<span>(</span></span><span>json_decode<span>(</span></span><span>"Hello World"</span><span>)</span><span>)</span><span>;</span><span> //null</span></code>