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If you have ever encountered the error message "PHP Warning: Cannot modify header information – headers already sent" when using PHP to develop a website or application, then you must know how troublesome it is. Although this error can be annoying when it appears, there are many simple and effective ways to fix it. This article details the causes of this error and common solutions, hoping to help you better solve this problem.
First, let us understand the cause of this error. In PHP, when we want to modify the HTTP header sent by the server to the browser, we must use the header() function at the beginning of our PHP script. However, if there is any output before this (including spaces, HTML tags, echo or print functions), then the function will not work properly and the error message "PHP Warning: Cannot modify header information – headers already sent" will be displayed. .
After understanding the cause of this error, here are some common solutions:
<?php ob_start(); ?>
Then anywhere in your script that needs to output something, use the following code to add content to the buffer Area:
<?php echo "Hello World!"; ?>
Finally, close the buffer before the header() function and output all the contents in the buffer:
<?php ob_end_flush(); ?>
Using the output_buffering function is a very effective way to solve "Cannot modify header information – headers already sent” error. Note, however, that if your script takes a long time to execute, the buffer size will also be very large and may crash the server. In this case, you need to change the size of the buffer according to the actual situation.
Conclusion
In short, although the "Cannot modify header information - headers already sent" error seems troublesome, in essence, it is just because before calling the header() function There is output. So we can easily solve this problem by just making sure there is no output before calling the header() function. If you still can't resolve the issue by following the methods above, please double-check your code and server settings, or seek professional help.
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