json_encode和json_decode和isset和array_key_exists

1.json_decode()

json_decode — 对 JSON 格式的字符串进行编码 

       说明

mixed json_decode ( string $json [, bool $assoc ] )

接受一个 JSON 格式的字符串并且把它转换为 PHP 变量 

 

       参数

json

待解码的 json string 格式的字符串。

assoc

当该参数为 TRUE 时，将返回 array 而非 object 。 

json_decode($data）输出的是对象,而json_decode("$arr",true)是把它强制生成PHP关联数组.

2.json_encode() 

string json_encode ( mixed $value [, int $options = 0 ] ) 

该函数只能接受 UTF-8 编码的数据

options 
由以下常量组成的二进制掩码： JSON_HEX_QUOT, JSON_HEX_TAG, JSON_HEX_AMP, JSON_HEX_APOS, JSON_NUMERIC_CHECK, JSON_PRETTY_PRINT, JSON_UNESCAPED_SLASHES, JSON_FORCE_OBJECT, JSON_UNESCAPED_UNICODE. 

 <?php
 $a = array('<foo>',"'bar'",'"baz"','&blong&', "\xc3\xa9");

 echo "Normal: ", json_encode($a), "\n"; //Normal: ["<foo>","'bar'","\"baz\"","&blong&","\u00e9"]
 echo "Tags: ", json_encode($a, JSON_HEX_TAG), "\n";//Tags: ["\u003Cfoo\u003E","'bar'","\"baz\"","&blong&","\u00e9"]
 echo "Apos: ", json_encode($a, JSON_HEX_APOS), "\n";//Apos: ["<foo>","\u0027bar\u0027","\"baz\"","&blong&","\u00e9"]
 echo "Quot: ", json_encode($a, JSON_HEX_QUOT), "\n";//Quot: ["<foo>","'bar'","\u0022baz\u0022","&blong&","\u00e9"]
 echo "Amp: ", json_encode($a, JSON_HEX_AMP), "\n";//Amp: ["<foo>","'bar'","\"baz\"","\u0026blong\u0026","\u00e9"]
 echo "Unicode: ", json_encode($a, JSON_UNESCAPED_UNICODE), "\n";//Unicode: ["<foo>","'bar'","\"baz\"","&blong&","é"]
 echo "All: ", json_encode($a, JSON_HEX_TAG | JSON_HEX_APOS | JSON_HEX_QUOT | JSON_HEX_AMP | JSON_UNESCAPED_UNICODE), "\n\n";// All: ["\u003Cfoo\u003E","\u0027bar\u0027","\u0022baz\u0022","\u0026blong\u0026","é"]

 $b = array();

 echo "Empty array output as array: ", json_encode($b), "\n";//Empty array output as array: []
 echo "Empty array output as object: ", json_encode($b, JSON_FORCE_OBJECT), "\n\n";//Empty array output as object: {}

 $c = array(array(1,2,3));

 echo "Non-associative array output as array: ", json_encode($c), "\n";//Non-associative array output as array: [[1,2,3]]
 echo "Non-associative array output as object: ", json_encode($c, JSON_FORCE_OBJECT), "\n\n";//Non-associative array output as object: {"0":{"0":1,"1":2,"2":3}}

 $d = array('foo' => 'bar', 'baz' => 'long');

 echo "Associative array always output as object: ", json_encode($d), "\n";//Associative array always output as object: {"foo":"bar","baz":"long"}
 echo "Associative array always output as object: ", json_encode($d, JSON_FORCE_OBJECT), "\n\n";//Associative array always output as object: {"foo":"bar","baz":"long"}
 ?>

可以看出json_encode()和json_decode()是编译和反编译过程，注意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。

 

3.php array_key_exists和isset区别：

php array_key_exists用于检查某个键名是否存在于数组中，而isset也可以用于检测数组中某个键名是否存在，那么二者有什么区别？

 一个基本的区别是isset（）可用于数组和变量，而array_key_exits()只能用于数组。

array_key_exists()

array_key_exists() 会检查键值的存在. 这个函数会返回TRUE，只要键值存在，即使值为NULL.

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$arr = array( "one"=>"1", "two"=>"2", "three"=>null ); array_key_exists("one", $arr); // true array_key_exists("two", $arr); // true array_key_exists("three", $arr); // true

 isset()

和arrry_key_exitst()不同，isset()会同时检查键和值，只有当健存在，对应的变量不为NUll的时候才会返回TURE

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$arr = array( "one"=>"1", "two"=>"2", "three"=>null ); isset($arr["one"]); // true isset($arr["two"]); // true isset($arr["three"]); // false