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>></span><span>1</span><span>,</span><span>'b'</span><span>=</span><span>></span><span>2</span><span>,</span><span>'c'</span><span>=</span><span>></span><span>3</span><span>,</span><span>'d'</span><span>=</span><span>></span><span>4</span><span>,</span><span>'e'</span><span>=</span><span>></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>></span><span>body</span> <span>=</span> <span>'another post'</span><span>;</span> <span>$obj</span><span>-</span><span>></span><span>id</span> <span>=</span> <span>21</span><span>;</span> <span>$obj</span><span>-</span><span>></span><span>approved</span> <span>=</span> <span>true</span><span>;</span> <span>$obj</span><span>-</span><span>></span><span>favorite_count</span> <span>=</span> <span>1</span><span>;</span> <span>$obj</span><span>-</span><span>></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>></span><span>'one'</span><span>,</span> <span>'2'</span><span>=</span><span>></span><span>'two'</span><span>,</span> <span>'3'</span><span>=</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>></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>></span> <span>int<span>(</span></span><span>1</span><span>)</span> <span>[</span><span>"b"</span><span>]</span> <span>=</span><span>></span> <span>int<span>(</span></span><span>2</span><span>)</span> <span>[</span><span>"c"</span><span>]</span> <span>=</span><span>></span> <span>int<span>(</span></span><span>3</span><span>)</span> <span>[</span><span>"d"</span><span>]</span> <span>=</span><span>></span> <span>int<span>(</span></span><span>4</span><span>)</span> <span>[</span><span>"e"</span><span>]</span> <span>=</span><span>></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>></span> <span>int<span>(</span></span><span>1</span><span>)</span> <span>[</span><span>"b"</span><span>]</span> <span>=</span><span>></span> <span>int<span>(</span></span><span>2</span><span>)</span> <span>[</span><span>"c"</span><span>]</span> <span>=</span><span>></span> <span>int<span>(</span></span><span>3</span><span>)</span> <span>[</span><span>"d"</span><span>]</span> <span>=</span><span>></span> <span>int<span>(</span></span><span>4</span><span>)</span> <span>[</span><span>"e"</span><span>]</span> <span>=</span><span>></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>

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