Using initializer_list

You can use initializer_list objects in your code by including the initializer_list header file. The template class has begin() and end() members, and you can use them to access list elements. It also has a size() member that returns the number of elements. Listing 16.22 shows a simple example using initializer_list. It requires a compiler that supports this C++11 feature.

Listing 16.22. ilist.cpp

// ilist.cpp -- use initializer_list (C++11 feature)
#include <iostream>
#include <initializer_list>

double sum(std::initializer_list<double> il);
double average(const std::initializer_list<double> & ril);

int main()
{
    using std::cout;

    cout << "List 1: sum = " << sum({2,3,4})
         <<", ave = " << average({2,3,4}) << ' ';
    std::initializer_list<double> dl = {1.1, 2.2, 3.3, 4.4, 5.5};
    cout << "List 2: sum = " << sum(dl)
         <<", ave = " << average(dl) << ' ';
    dl = {16.0, 25.0, 36.0, 40.0, 64.0};
    cout << "List 3: sum = " << sum(dl)
         <<", ave = " << average(dl) << ' ';
    return 0;
}

double sum(std::initializer_list<double> il)
{
    double tot = 0;
    for (auto p = il.begin(); p !=il.end(); p++)
        tot += *p;
    return tot;
}

double average(const std::initializer_list<double> & ril)
{
    double tot = 0;
    int n = ril.size();
    double ave = 0.0;
    if (n > 0)
    {
        for (auto p = ril.begin(); p !=ril.end(); p++)
            tot += *p;
        ave = tot / n;
    }
    return ave;
}

Here’s a sample run:

List 1: sum = 9, ave = 3
List 2: sum = 16.5, ave = 3.3
List 3: sum = 181, ave = 36.2