How to detect the size of the parameters that are passed through ellipsis in C++?

Question

The answer to this question says that C doesn't provide any means to detect the size of parameter passed through ellipsis:
How to detect the size of the parameters that are passed through ellipsis?

Is there C++ solution to this problem?

Answer 1

For C style vararg functions, no. For C++ style vararg templates, yes. You use sizeof ... operator for that. See cppreference:

#include <iostream>

template <typename ...Args>
void print_arg_cnt(Args... args)
{
    std::cout << "Arg count: " << sizeof ...(Args) << '\n'; 
}

int main()
{
    print_arg_cnt(1, 1.1, 'a');
}

Arg count: 3

Godbolt

If you want to find out the total number of bytes those arguments occupy, you can do this:

template <typename ...Args>
void print_args_size(Args... args)
{
    auto constexpr size = (sizeof(Args) + ... + 0); // +0 for the empty case
    std::cout << "Total size: " << size << '\n';
}

Or sizes can be printed individually as in cigien's answer.