Analysis of error causes and solutions of php session_start of

Error: Warning: session_start() [function.session-ES6en]: Cannot send cache ES11en-ES12en already sent

Reason: If there is output before session_start(), an error occurs,

Solution: Add ob_start() before session_start();

index.php

<?php 
error_reporting(-1); 
ob_start();// Can't write without an error session 
register_shutdown_function('close'); 

  
echo 1; 
 session_start(); 

$_SESSION['password']='mima2ddddddddddddddda2'; 

function close() 
    { 
        if(session_id()!=='') 
            @session_write_close(); 
    } 
?> 
<a href="index2.php" >index2</a> 

<?php 
error_reporting(-1); 
ob_start();// Not adding will cause an error and cannot be read session 
?
echo 1; 
 session_start(); 

echo $_SESSION['password']; 
var_dump($_SESSION); 
?> 
<a href="index.php" >index</a>