Php操作json方法
<h2> </h2><p> 一、json_encode()</p>
<p> 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：</p>
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<pre>1 $arr = array ('a'=>1,'b'=>2,'c'=>3,'d'=>4,'e'=>5);
2
3 echo json_encode($arr);
4
5 // 结果为
6{"a":1,"b":2,"c":3,"d":4,"e":5}</pre>
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<p> 再看一个对象转换的例子：</p>
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<pre> 1 $obj->body = 'another post';
2
3 $obj->id = 21;
4
5 $obj->approved = true;
6
7 $obj->favorite_count = 1;
8
9 $obj->status = NULL;
10
11 echo json_encode($obj);
12
13 // 结果为
14
15 {
16 "body":"another post",
17
18 "id":21,
19
20 "approved":true,
21
22 "favorite_count":1,
23
24 "status":null
25 }</pre>
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<p> 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。</p>
<p> </p>
<p> 二、索引数组和关联数组</p>
<p> 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）。</p>
<p> 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。</p>
<p> 比如，现在有一个索引数组</p>
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<pre>1 $arr = Array('one'， 'two'， 'three');
2 echo json_encode($arr);</pre>
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<p> 结果为：</p>
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<pre>["one"，"two"，"three"]</pre>
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<p> 如果将它改为关联数组：</p>
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<pre>1 $arr = Array('1'=>'one'， '2'=>'two'， '3'=>'three');
2 echo json_encode($arr);</pre>
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<p> 结果就变了：</p>
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<pre> {"1":"one"，"2":"two"，"3":"three"}</pre>
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<p> 注意，数据格式从"[]"（数组）变成了"{}"（对象）。</p>
<p> 如果你需要将"索引数组"强制转化成"对象"，可以这样写</p>
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<pre>json_encode( (object)$arr );</pre>
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<p> 或者</p>
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<pre>json_encode ( $arr, JSON_FORCE_OBJECT );</pre>
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<p> </p>
<p>三、类（class）的转换</p>
<p> 下面是一个PHP的类：</p>
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<pre><span style="color: rgba(0, 128, 128, 1)"> 1</span> <span style="color: rgba(0, 0, 0, 1)">class Foo {
</span><span style="color: rgba(0, 128, 128, 1)"> 2</span>
<span style="color: rgba(0, 128, 128, 1)"> 3</span> const ERROR_CODE = '404'<span style="color: rgba(0, 0, 0, 1)">;
</span><span style="color: rgba(0, 128, 128, 1)"> 4</span>
<span style="color: rgba(0, 128, 128, 1)"> 5</span> public $public_ex = 'this is public'<span style="color: rgba(0, 0, 0, 1)">;
</span><span style="color: rgba(0, 128, 128, 1)"> 6</span>
<span style="color: rgba(0, 128, 128, 1)"> 7</span> private $private_ex = 'this is private!'<span style="color: rgba(0, 0, 0, 1)">;
</span><span style="color: rgba(0, 128, 128, 1)"> 8</span>
<span style="color: rgba(0, 128, 128, 1)"> 9</span> protected $protected_ex = 'this should be protected'<span style="color: rgba(0, 0, 0, 1)">;
</span><span style="color: rgba(0, 128, 128, 1)">10</span>
<span style="color: rgba(0, 128, 128, 1)">11</span> public <span style="color: rgba(0, 0, 255, 1)">function</span><span style="color: rgba(0, 0, 0, 1)"> getErrorCode() {
</span><span style="color: rgba(0, 128, 128, 1)">12</span>
<span style="color: rgba(0, 128, 128, 1)">13</span> <span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> self::ERROR_CODE;
</span><span style="color: rgba(0, 128, 128, 1)">14</span>
<span style="color: rgba(0, 128, 128, 1)">15</span> <span style="color: rgba(0, 0, 0, 1)">}
</span><span style="color: rgba(0, 128, 128, 1)">16</span>
<span style="color: rgba(0, 128, 128, 1)">17</span> }</pre>
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<p> </p>
<p> 现在，对这个类的实例进行json转换：</p>
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<pre>$foo = <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> Foo;
$foo_json </span>=<span style="color: rgba(0, 0, 0, 1)"> json_encode($foo);
echo $foo_json;</span></pre>
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<p> 输出结果是</p>
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<pre>{"public_ex":"this is public"}</pre>
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<p> 可以看到，除了公开变量（public），其他东西（常量、私有变量、方法等等）都遗失了。</p>
<p> 四、json_decode()</p>
<p> 该函数用于将json文本转换为相应的PHP数据结构。下面是一个例子：</p>
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<pre>$json = '{"foo": 12345}'<span style="color: rgba(0, 0, 0, 1)">;
$obj </span>=<span style="color: rgba(0, 0, 0, 1)"> json_decode($json);
print $obj</span>->{'foo'}; <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 12345</span></pre>
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<p> 通常情况下，json_decode()总是返回一个PHP对象，而不是数组。比如：</p>
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<pre>$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}'<span style="color: rgba(0, 0, 0, 1)">;
var_dump(json_decode($json));</span></pre>
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<p> 结果就是生成一个PHP对象：</p>
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<pre>object(stdClass)#1 (5<span style="color: rgba(0, 0, 0, 1)">) {
[</span>"a"] => <span style="color: rgba(0, 0, 255, 1)">int</span>(1<span style="color: rgba(0, 0, 0, 1)">)
[</span>"b"] => <span style="color: rgba(0, 0, 255, 1)">int</span>(2<span style="color: rgba(0, 0, 0, 1)">)
[</span>"c"] => <span style="color: rgba(0, 0, 255, 1)">int</span>(3<span style="color: rgba(0, 0, 0, 1)">)
[</span>"d"] => <span style="color: rgba(0, 0, 255, 1)">int</span>(4<span style="color: rgba(0, 0, 0, 1)">)
[</span>"e"] => <span style="color: rgba(0, 0, 255, 1)">int</span>(5<span style="color: rgba(0, 0, 0, 1)">)
}</span></pre>
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<p> 如果想要强制生成PHP关联数组，json_decode()需要加一个参数true：</p>
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<pre>$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}'<span style="color: rgba(0, 0, 0, 1)">;
var_dump(json_decode($json,</span><span style="color: rgba(0, 0, 255, 1)">true</span>));</pre>
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<p> 结果就生成了一个关联数组：</p>
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<pre>array(5<span style="color: rgba(0, 0, 0, 1)">) {
[</span>"a"] => <span style="color: rgba(0, 0, 255, 1)">int</span>(1<span style="color: rgba(0, 0, 0, 1)">)
[</span>"b"] => <span style="color: rgba(0, 0, 255, 1)">int</span>(2<span style="color: rgba(0, 0, 0, 1)">)
[</span>"c"] => <span style="color: rgba(0, 0, 255, 1)">int</span>(3<span style="color: rgba(0, 0, 0, 1)">)
[</span>"d"] => <span style="color: rgba(0, 0, 255, 1)">int</span>(4<span style="color: rgba(0, 0, 0, 1)">)
[</span>"e"] => <span style="color: rgba(0, 0, 255, 1)">int</span>(5<span style="color: rgba(0, 0, 0, 1)">)
}</span></pre>
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<p> 五、json_decode()的常见错误</p>
<p> 下面三种json写法都是错的，你能看出错在哪里吗？</p>
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<pre>$bad_json = "{ 'bar': 'baz' }"<span style="color: rgba(0, 0, 0, 1)">;
$bad_json </span>= '{ bar: "baz" }'<span style="color: rgba(0, 0, 0, 1)">;
$bad_json </span>= '{ "bar": "baz"， }';</pre>
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<p> 对这三个字符串执行json_decode()都将返回null，并且报错。</p>
<p> 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）。</p>
<p> 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。</p>
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<pre>var_dump(json_decode("Hello World")); <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">null</span></pre>
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来源：https://www.cnblogs.com/xm-dream/p/11289191.html
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