How to explicitly load a binary module?

A binary module is a shared library that must have one entry point with a special name. For instance, if I have a binary module fred then its initialisation function must be called luaopen_fred. This code will explicitly load fred given a full path:

local fn,err = package.loadlib('/home/sdonovan/lua/clibs/fred.so','luaopen_fred')
if not fn then print(err)
else
 fn()
end

(For Windows, use an extension of .dll)

Note that any function exported by a shared library can be called in this way, as long as you know the name. When writing extensions in C++, it is important to export the entry point as extern "C", otherwise the name will be mangled. On Windows, you have to ensure that at least this entry point is exported via __declspec(dllexport) or using a .def file.