php session_start()出错原因分析及解决方法

错误提示： Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent

原因：在session_start()之前如果有输出内容，会出错，

解决办法：在session_start()之前加上ob_start();

index.php 
代码如下:
<?php
error_reporting(-1);
ob_start();//不加会出错，无法写入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>

index2.Php
代码如下:
<?php
error_reporting(-1);
ob_start();//不加会出错，无法读取session
?
echo 1;
 session_start();

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