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?