http://kor.i2p/books/The%20C%20Programming%20Language%20by%20K&R/appa.html
If the function declaration in scope for a call is new-style, then the
arguments are converted, as if by assignment, to the types of the corresponding
parameters of the function's prototype. The number of arguments must be the
same as the number of explicitly described parameters, unless the declaration's
parameter list ends with the ellipsis notation (, ...) .