Other people have wibbled about references, but in case you're trying to deal with data in some machine-specific C-generated format, or to generate data to pass to such (believe it or not there are some crazy programs that expect you to drive them by dropping a C struct in a file, or even pass them a struct on STDIN), then you might want Convert::Binary::C.

I've not used it myself, but trying it out is on my to-do list for solving one of those thorny problems.