PHP to implement a member account can only login code instances

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Scene reproduction

The same member account limit on the same device (computer, mobile phone, ipad, etc.) on a single sign-on, repeated login, the original login to access the page directly to the login page and need to re-login to normal access.

Principle Analysis

A account on a computer login, a account at this time again with B computer login again, a computer request page, prompt "re-login" information, and jump to the login page

Thinking Analysis:

A account is logged on a computer, the session ID is written to the TXT file, each time you visit the page, do a check (compare the value of the TXT file is the same as the value of the current login session_id)

Instance

1. Entrance and calibration (index.php)

<?phpsession_start (); $uid = 10;if (Is_login ($uid)) {header (' location:loginSuccess.php ');} else{  $getLogSessionId = file_get_contents (' session_log/'. $uid. TXT ');  if ($getLogSessionId) {    echo "has been logged in elsewhere, please login again";    echo "<br>";    echo "Jump to login page after 5 seconds!";    Header ("refresh:5;url=login.php");  } else{      echo ' first login ... ';      echo "<br>";      echo "Jump to the login page after 3 seconds!";    Header ("refresh:3;url=login.php");}  } /*** is compared to the session_id generated by writing a file at login session_id and the current login device, the same device is logged in, and the other one is logged in */function Is_login ($uid) {  $ Getlogsessionid = file_get_contents (' session_log/'. $uid. TXT ');    if ($getLogSessionId = = session_id ()) {      return true;  } else{      return false;  }}

2. Login (login.php)

<?phpsession_start (); echo "Login ...."; Echo ' <br> '; $uid = 10;file_put_contents (' session_log/'. $uid. TXT ', session_id ()); echo "Login Complete";

3. Successful Login (loginsuccess.php)

<?phpecho "I am logged in successfully!";

4, Save SessionID folder (session_log), test code, need to manually build one or give automatically generated file permissions