为什么在定义 session 时出现“未定义索引”错误？

Question

I am new to PHP and sessions so go easy on me. This is my code

if(isset($_POST["username"]) || isset($_SESSION["username"])){
   $_SESSION["username"] = $_POST["username"];
   echo $_SESSION["username"];
   } else {
     exit();
   }
   
  

I'm getting an undefined index in the line that is supposed to define $SESSION["username"]. What am I doing wrong?

Answer 1

I figured it out. The problem occurs if isset($_POST["username"]) is false. Then when $_POST["username"] doesn't exist so it returns an error

Answer 2

try it

if(isset($_POST["username"])){
 $_SESSION["username"] = $_POST["username"];
 echo $_SESSION["username"];
} else if (isset($_SESSION["username"])) {
 echo $_SESSION["username"];
} else {
 exit();
}

you're checking if your $_POST variable is set or $_SESSION variable is set, so what's happening here is your if statement is returning true because your $_SESSION variable is already set. And don't forget to start your session using session_start()