What does its means void interrupt (*oldisr)(...);

elipses (...) as function arguments means that the function takes a variable argument list - i.e. it can take any number of parameters of arbitrary types. Unfortunately you can't process any of the arguments as you haven't got a named parameter in the arguments list. In this case it looks like whoever's using it is telling the compiler to not bother generating code to remove parameters from the stack as it's an interrupt handler.

This sort of thing turns up a fair bit in C (well, generally with one named argument) but generally in C++ you don't tend to use it. If you want variable arguments in C++ you tend to use overloading and chaining (the way the stream insertion and extraction operators work) as this keeps type safety.

Cheers,

Ash

PS: If you want more information about processing variable argument lists then look up the macros va_list, va_start, va_arg and va_end in your compiler's documentation, textbook or online.