How to put a part of variable argument list into another function?

Question

I'm dealing with such a problem, I have function f(std::initializer_list<double> list),and I want to put a part of variable argument list (the second variable argument to end) into another function like:

void f(std::initializer_list<double> list){
    f1(*(list.begin()+1,...,*(list.end-1));
}

The f1 function is normal function like void f1(double x) or void f1(double x1,double x2), I want f can do with different variable argument number of f1, how can I get it?

Answer 1

An initializer list does not seem to have constructors which take a pair of iterators, see here. But you can use a span for that:

#include<iostream>
#include<span>

void f1(double a, double b)
{
}

void f2(auto list)
{
    for(auto i : list)
    {
        std::cout<<i<<std::endl;
    }
}

void f(std::initializer_list<double> list){
    size_t size = std::distance(std::begin(list),std::end(list))-1;
    auto list = std::span{std::next(std::begin(list)), size};
    f1(list[0],list[1]);
    f2(list);
}

int main()
{
    auto a = std::initializer_list<double>{1.0,2.0,3.0};
    f(a);
}

DEMO

Note that the previous code can be made more generic. But it should be ok to get the idea.