variadic-functions

Here I found an example of how varargs can be used in C. #include <stdarg.h> double average(int count, ...) { va_list ap; int j; double tot = 0; va_start(ap, count); //Requires the last fixed parameter (to get the address) for(j=0; j<count; j++) tot+=va_arg(ap, double); //Requires the type to cast to. Increments ap to the next argument. va_end(ap); return tot/count; } I can understand this example only to some extent. It is not clear to me why we use va_start(ap, count); . As far as I understand, in this way we set the iterator to its first element. But why it is not set to the beginning by

Consider the method declaration: String.format(String, Object ...) The Object ... argument is just a reference to an array of Object s. Is there a way to use this method with a reference to an actual Object array? If I pass in an Object array to the ... argument - will the resultant argument value be a two-dimensional array - because an Object[] is itself an Object : Object[] params = ....; // Make the array (for example based on user-input) String s = String.format("%S has %.2f euros", params); So the first component of the array (Which is used in the String.format method), will be an array

I have a PHP function that takes a variable number of arguments (using func_num_args() and func_get_args() ), but the number of arguments I want to pass the function depends on the length of an array. Is there a way to call a PHP function with a variable number of arguments? If you have your arguments in an array, you might be interested by the call_user_func_array function. If the number of arguments you want to pass depends on the length of an array, it probably means you can pack them into an array themselves -- and use that one for the second parameter of call_user_func_array . Elements of

I have a class that holds an "error" function that will format some text. I want to accept a variable number of arguments and then format them using printf. Example: class MyClass { public: void Error(const char* format, ...); }; The Error method should take in the parameters, call printf/sprintf to format it and then do something with it. I don't want to write all the formatting myself so it makes sense to try and figure out how to use the existing formatting. void Error(const char* format, ...) { va_list argptr; va_start(argptr, format); vfprintf(stderr, format, argptr); va_end(argptr); } If

I want to write a simple adder (for giggles) that adds up every argument and returns a sum with appropriate type. Currently, I've got this: #include <iostream> using namespace std; template <class T> T sum(const T& in) { return in; } template <class T, class... P> auto sum(const T& t, const P&... p) -> decltype(t + sum(p...)) { return t + sum(p...); } int main() { cout << sum(5, 10.0, 22.2) << endl; } On GCC 4.5.1 this seems to work just fine for 2 arguments e.g. sum(2, 5.5) returns with 7.5. However, with more arguments than this, I get errors that sum() is simply not defined yet. If I

Shouldn’t this definition be allowed in a lazy language like Haskell in which functions are curried? apply f [] = f apply f (x:xs) = apply (f x) xs It’s basically a function that applies the given function to the given list of arguments and is very easily done in Lisp for example. Are there any workarounds? Don Stewart It is hard to give a static type to the apply function, since its type depends on the type of the (possibly heterogeneous) list argument. There are at least two ways one way to write this function in Haskell that I can think of: Using reflection We can defer type checking of the