In C and C++, the ellipsis is used in the formal parameter list of a function to indicate that the function has a variable number of arguments.

For example:

int foo (int a, int b, ...)

tells the compiler that foo takes at least two arguments, and possibly more.

In the body of the function, use the macros va_start and va_arg to extract the values of the arguments.

You should avoid variable arguments like the plague in C and never use variable arguments in C++.