What is this at the end of function ,...) in c++

Answer 1

It means the function can take any number of extra arguments. For example, consider printf; the first argument is the format string, and then there can be any number of arguments after that for all of the modifiers. This would be represented by using ... after the first argument when defining the function.

Answer 2

That specifies a variable number of arguments which can be accessed using the macros in the cstdarg header.