为什么我会收到“无法修改标头信息”和“未定义索引”错误？ [重复]

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• How to fix “Headers already sent” error in PHP 11 answers

I have a small php script thats working fine on server but not locally, I tried a lot but can't seem to get rid of these errors and login:

Notice: Undefined index: page in /Users/myusername/Work/www/sabaqk/index.php on line 4

Notice: Undefined index: page in /Users/myusername/Work/www/sabaqk/class/account.class.php on line 26

Warning: Cannot modify header information - headers already sent by (output started at /Users/myusername/Work/www/sabaqk/index.php:4) in /Users/myusername/Work/www/sabaqk/class/account.class.php on line 68

Warning: Cannot modify header information - headers already sent by (output started at /Users/myusername/Work/www/sabaqk/index.php:4) in /Users/myusername/Work/www/sabaqk/class/account.class.php on line 69

Warning: Cannot modify header information - headers already sent by (output started at /Users/myusername/Work/www/sabaqk/index.php:4) in /Users/myusername/Work/www/sabaqk/class/account.class.php on line 70

Warning: Cannot modify header information - headers already sent by (output started at /Users/myusername/Work/www/sabaqk/index.php:4) in /Users/myusername/Work/www/sabaqk/class/account.class.php on line 71

Warning: Cannot modify header information - headers already sent by (output started at /Users/myusername/Work/www/sabaqk/index.php:4) in /Users/myusername/Work/www/sabaqk/class/account.class.php on line 72

I'd really appreciate any help. Thanks!

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Answer 1

As I stated in comments, Your web server probably has notices and warnings disabled in error reporting and your local host does not. Since your local host has notices enabled, those notice errors are getting printed out near the beginning of your script, which is messing up the rest. When you attempt to set your sessions/cookies (whatever you're using), PHP is unable to do so because content (your errors) has already been sent and the headers along with it, so cookies can't be set anymore.

Do not just disable error reporting in your PHP script because 1) you won't fix the underlying issue and 2) those errors will still get sent to your Apache error log and the log will become a massive text file of worthless information.

This is a very simple issue to fix. Just check if your keys exist before attempting to use them, either using array_key_exists() if it's an array, or even simpler, just using isset(). This will get rid of your notice errors and ultimately eliminate your login problem.