Warning: Cannot modify header information出现这样的情况如何解决？

Warning: Cannot modify header information - headers already sent by (output started at /home/lprcpoi/public_html/upload3_3.php:3) in /home/lprcpoi/public_html/upload3_3.php on line 362

可以在PHP文档的头尾加上ob_start（）和ob_end_flush();

附上手册中的代码：

<?php

function callback($buffer)
{
  // replace all the apples with oranges
  return (str_replace("apples", "oranges", $buffer));
}

ob_start("callback");

?>
<html>
<body>
<p>It's like comparing apples to oranges.</p>
</body>
</html>
<?php

ob_end_flush();

?>