php json 관련 함수의 사용예에 대한 자세한 설명

$arr=array("A"=>"a","B"=>"b","C"=>"c","D"=>"d");
echo json_encode($arr);

{"A":"a","B":"b","C":"c","D":"d"}

$arr='{"A":"a","B":"b","C":"c","D":"d"}';
var_dump(json_decode($arr));
var_dump(json_decode($arr,true));

object(stdClass)[1]
 public 'A' => string 'a' (length=1)
 public 'B' => string 'b' (length=1)
 public 'C' => string 'c' (length=1)
 public 'D' => string 'd' (length=1)
array (size=4)
 'A' => string 'a' (length=1)
 'B' => string 'b' (length=1)
 'C' => string 'c' (length=1)
 'D' => string 'd' (length=1)