Question

I’m using set_cookie() on a site. After adding some functionality, I’m getting Warning: Cannot modify header information - headers already sent by... error. The line number it references as to where the headers initiated from is the very line where set_cookie() is! And I checked, it’s not being called twice.

How can I track down these premature headers? I looked at the source code and didn’t see any stray characters or anything before the error message starts ( I’m using xdebug, so the first thing is a
, which I thought was me, but is actually the beginning of the xdebug message ). I’ve grepped my code for extra echo and so forth — nothing.

Can PHP tell me when and where the headers are starting? Or are they really starting on the set_cookie line, and if so, how have I gotten myself into this situation, and how do I get out?

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edit: I’m not sure I can paste the code — do you want just the set_cookie() line? I thought the headers were coming out before that. And there’s a lot going on before that with different classes being instantiated. And also I don’t think I can post all the classes and stuff — you know, proprietary information 😉

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Edit: I’ve gotten rid of all terminating delimiters ( all ?>s) and made sure that the first characters of every included file is <?. This is frustrating! It was working before I did these recent changes :(((

Also, why doesn’t headers_sent() work?

if ( headers_sent($filename, $linenum) ) { 
    echo "headers sent: $filename:$linenum."; 
}   
set_cookie(...); 

gives

headers sent: :0. 

Answer 1

I found it! It was a flush(); that I had left lying around all by itself in one of the pages. Surprisingly, it doesn’t correctly bind $filename and $linenumber to headers_sent().