I would like to get a list of the wireless networks available. Ideally this would be via some C call, but I don't mind if I have to kludge it with a system call. Even better if the required C call or program doesn't require some exotic 3rd party package.
The internet seems to suggest I use sudo iwlist <interface> scan which does seem to do the trick from the command line, but I'd rather not require root permissions. I only want to see the basics, not change anything.
The Wireless Tools package -- of which iwlist is a part -- also contains a Wireless Tools Helper Library. You need to include iwlib.h and link with libiw.a (i.e. add -liw). Then look up the documentation for the iw_set_ext function. The SIOCSIWSCAN parameter will be of most use. For an example of how to use this interface, take a look at the KWifiManager source in the KDE library (see: Interface_wireless_wirelessextensions::get_available_networks method). Alternatively, you can also download the Wireless Tools source code and take a look at how the iwlib iw_set_ext function is also used for scanning in iwlist.c.
As for privileges, I imagine the process will need to run as root to perform the scan. I'd love to know if this could be done otherwise as well.
Since you are using Ubuntu 8.04 the libiw-dev package should be of use.