session_start函数

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本文详细介绍了PHP中session_start()函数的用法，包括如何初始化会话、使用命名会话、处理输出缓存和输出压缩，以及如何在页面间传递会话数据。通过实例演示了如何在两个页面之间共享数据。

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session_start

(PHP 4, PHP 5)

session_start — Initialize session data

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Description

bool session_start ( void )

session_start() creates a session or resumes the current one based on a session identifier passed via a GET or POST request, or passed via a cookie.

To use a named session, call session_name() before calling session_start().

When session.use_trans_sid is enabled, the session_start() function will register an internal output handler for URL rewriting.

If a user uses ob_gzhandler or similar with ob_start(), the function order is important for proper output. For example, ob_gzhandlermust be registered before starting the session.

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Return Values

This function returns TRUE if a session was successfully started, otherwise FALSE.

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Changelog

Version	Description
5.3.0	If a session fails to start, then `FALSE` is returned. Previously `TRUE` was returned.
4.3.3	As of PHP 4.3.3, calling session_start() after the session was previously started will result in an error of level `E_NOTICE`. Also, the second session start will simply be ignored.

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Examples

Example #1 A session example: page1.php

<?php
 // page1.php
 
 session_start();
 
 echo 'Welcome to page #1';
 
 $_SESSION['favcolor'] = 'green';
 $_SESSION['animal']   = 'cat';
 $_SESSION['time']     = time();
 
 // Works if session cookie was accepted
 echo '<br /><a href="page2.php">page 2</a>';
 
 // Or maybe pass along the session id, if needed
 echo '<br /><a href="page2.php?' . SID . '">page 2</a>';
 ?>

After viewing page1.php, the second page page2.php will magically contain the session data. Read the session reference for information on propagating session ids as it, for example, explains what the constant SID is all about.

Example #2 A session example: page2.php

<?php
 // page2.php
 
 session_start();
 
 echo 'Welcome to page #2<br />';
 
 echo $_SESSION['favcolor']; // green
 echo $_SESSION['animal'];   // cat
 echo date('Y m d H:i:s', $_SESSION['time']);
 
 // You may want to use SID here, like we did in page1.php
 echo '<br /><a href="page1.php">page 1</a>';
 ?>