session_unset()与session_destroy()

session_unset():释放当前在内存中已经创建的所有$_SESSION变量，但不删除session文件以及不释放对应的session id;

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session_destroy():删除当前用户对应的session文件以及释放session id，内存中的$_SESSION变量内容依然保留;

For example:

    session_start();//  echo "<br/>---1----<br/>";//  $pg_uid=1;//  $_SESSION['pg_name']='boys';//  $_SESSION['pg_sex']=1;//  $_SESSION['pg_theme']='default';//  var_dump($_SESSION);//  echo "<br/>-----2-----<br/>";//  unset($_SESSION['pg_name']);//  unset($_SESSION['pg_theme']);//  session_unset('pg_sex');//  session_unset('pg_uid');//  var_dump($_SESSION);    echo "<br/>----3------<br/>";    $_SESSION['pg_members']=5;    $_SESSION['pg_girls']=6;    session_unset($_SESSION);    var_dump($_SESSION);    echo "<br/>----4------<br/>";    $_SESSION['pg_boss']=3;    $_SESSION['pg_girls']=6;    session_destroy();    var_dump($_SESSION);//  echo "<br/>----5-----<br/>";//  session_unset('pg_boss');//     var_dump($_SESSION);//     fopen(__FILE__,"r");

output:

----3------array (size=0)  empty----4------array (size=2)  'pg_boss' => int 3  'pg_girls' => int 6