Function declarations in which the last member of argument-declaration-list is the ellipsis (...) can take a variable number of arguments. In these cases, C++ provides type checking only for the explicitly declared arguments. You can use variable argument lists when you need to make a function so general that even the number and types of arguments can vary. The printf family of functions is an example of functions that use variable argument lists.
To access arguments after those declared, use the macros contained in the standard include file STDARG.H as described in Functions with Variable Argument Lists.
Microsoft Specific
Microsoft C++ allows the ellipsis to be specified as an argument if the ellipsis is the first argument and the ellipsis is preceded by a comma. Therefore, the declaration int Func( int i, ... ); is legal, but int Func( int i ... ); is not.
END Microsoft Specific
Declaration of a function that takes a variable number of arguments requires at least one “placeholder” argument, even if it is not used. If this place-holder argument is not supplied, there is no way to access the remaining arguments.
When arguments of type char are passed as variable arguments, they are converted to type int. Similarly, when arguments of type float are passed as variable arguments, they are converted to type double. Arguments of other types are subject to the usual integral and floating-point promotions. See Integral Promotions in Chapter 3 for more information.