为什么两个不同文件中的session_start（）导致php网页出错？ [重复]

This question already has an answer here:

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I use session_start() function in a php file named image.func.php, then I include this file in another file named include.php, and in the include.php, I use session_start()function again.

When I run the php file, there is no output on the web page. But after I annotate one of session_start(), php web page runs successfully.

So, why cannot use two session_start() in a project?

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