json_decode返回null 和synax error原因及处理

$checkLogin ='[{"gdsincode":"1103293","gdsname":"鲜美来带鱼段800ｇ","nowamount":0.000,"shopprice":18.00,"stockinstd":1.00,"baseunit":"袋","brandcode":"00","brand":"不详","syn_id":"93482,142373","mac":"b2ca21a6b25835a9"}]';
for ($i = 0; $i <= 31; ++$i) {
     $checkLogin = str_replace(chr($i), "", $checkLogin);
}
$checkLogin = str_replace(chr(127), "", $checkLogin);

// This is the most common part
// Some file begins with 'efbbbf' to mark the beginning of the file. (binary level)
// here we detect it and we remove it, basically it's the first 3 characters 
if (0 === strpos(bin2hex($checkLogin), 'efbbbf')) {
    $checkLogin = substr($checkLogin, 3);
}

var_Dump(json_decode($checkLogin, true));