Ask why, Json_decode turn uft-8 string, result is null

Excuse me, why, Json_decode to uft-8 string, the result is null?

 
 
 

 
 
$str =isset ($_post["text"])? Filter_input (Input_post, "text", filter_sanitize_special_chars): ';
print "$str =". $str. " \ n ";
if (strlen ($STR) >0) {
$str =mb_convert_encoding ($str, "GBK", "UTF-8");
$jo =json_decode ($STR);  Chinese, turn out to be null

$msg _id= $jo->msg_id; There will be an error here.
}


Echo ';


?>

------Solution--------------------
JSON format is not right, you put J to convert the JSON string echo out to see if it conforms to the standard JSON format
------Solution--------------------
Plus the back.
is not already in JSON format.
------Solution--------------------
Print_r ("\n++++\n". $jo. " \n====\n ");
What is this?

------Solution--------------------
echo $_post["text"];
Let's see what it is, it's mostly escaped with quotes.

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