In a publicly installed headers, a few functions are declared without any arguments at all, a la "()".
When I used gcc's -Wimplict and -Wstrict-prototypes to check for the mismatch of
function prototype declarations and their usage in my own program,
some headers from libupnp-1.6.6 produced warnings.
They are not strictly bugs, but pretty much annoying. This is 2009, and almost all the important compilers
So the offending functions are declared as "(void") to show that they have no arguments at all.