Question

Which disadvantages could I have if I want to use the function

foo(int num, ...)

to implement the variable number of arguments?

I do know the first disadvantage that you can only use one data type.

Is there any way else to do that?

Answer 1

There are multiple ways NOT to use ellipsis notation.

Why ? Because of type safety a hazardous manipulations of the primitives (va_start, va_arg, va_next) that you can’t really forward to another function etc…

However, contrary to C, C++ provides template methods, which offer type safety and generic behavior, and this can be cumulated with overloads:

template <typename Arg0>
void foo(int num, Arg0 const& arg0);

template <typename Arg0, typename Arg1>
void foo(int num, Arg0 const& arg0, Arg1 const& arg1);

// ... etc

This is the current state of the art, which is generally helped by a subtle application of Preprocessor Programming (check out Boost.Preprocessor).

With the new C++0x standard, come the variadic templates, which offer the same facilities than the C variadic methods, with type safety offered (yeeha)

template <typename Arg0, typename... Args>
void foo(Arg0 arg0, Args... args)
{
  // Do something with arg0
  foo(args);
}

template <typename Arg0>
void foo(Arg0 arg0)
{
  // Do something with arg0
}

This also allows to define tuple classes much more easily 🙂