Variable number of arguments in C++?

Question

How can I write a function that accepts a variable number of arguments? Is this possible, how?

Answer 1

A C++17 solution: full type safety + nice calling syntax

Since the introduction of variadic templates in C++11 and fold expressions in C++17, it is possible to define a template-function which, at the caller site, is callable as if it was a varidic function but with the advantages to:

• be strongly type safe;
• work without the run-time information of the number of arguments, or without the usage of a "stop" argument.

Here is an example for mixed argument types

template
void print(Args... args)
{
    (std::cout << ... << args) << "\n";
}
print(1, ':', " Hello", ',', " ", "World!");

And another with enforced type match for all arguments:

#include  // enable_if, conjuction

template
using are_same = std::conjunction...>;

template::value, void>>
void print_same_type(Head head, Tail... tail)
{
    std::cout << head;
    (std::cout << ... << tail) << "\n";
}
print_same_type("2: ", "Hello, ", "World!");   // OK
print_same_type(3, ": ", "Hello, ", "World!"); // no matching function for call to 'print_same_type(int, const char [3], const char [8], const char [7])'
                                               // print_same_type(3, ": ", "Hello, ", "World!");
                                                                                              ^

More information:

1. Variadic templates, also known as parameter pack Parameter pack(since C++11) - cppreference.com.
2. Fold expressions fold expression(since C++17) - cppreference.com.
3. See a full program demonstration on coliru.