Technology Tales

Adventures & experiences in contemporary technology

Getting one’s HTTP headers in a twist

9th June 2007

I am in the process of further linking the content of hillwalking blog into the fabric of other parts of my website. To date, this has included adding a list of all the posts to the site map and a dossier of latest entries to the site’s welcome page. One things that started to crop up were a series of warnings of the form:

Cannot modify header information -- headers already sent by…

The cause of this was my calling a PHP script that was part of my hillwalking blog installation and this caused Bad Behaviour to be invoked. The result was that a HTTP header was being sent in order to create a cookie after one already had been sent to display a web page. A spot of conditional coding and the use of an extra flag resolved the problem.

Apparently, there is another surefire way of getting the same result: whitespace before or after the <?php … ?> tag in an included script. The cookie issue is one that I can understand but it does seem strange that an attempt is made to send HTTP header information when the latter arises. It causes loads of questions, though…

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