C++ Library - <initializer_list>

The <initializer_list> in C++ provides a convenient way to initialize containers and user-defined types with a list of values. It allows for more flexible and readable code by enabling the initialization of collections with a comma separated list of elements.

The <initializer_list> is a lightweight proxy object that allows a constructor to accept a list of values without explicitly specifying the type. It is used when working with standard library containers such as vector, set and map.

Including <initializer_list> Header

To include the <initializer_list> header in your C++ program, you can use the following syntax.

#include <initializer_list>

Functions of <initializer_list> Header

Below is list of all functions from <initializer_list> header.

Adding Values from an Initializer List

In the following example, we are going to calculate the sum of the elements from the initializer_list.

#include <iostream>
#include <initializer_list>
int a(std::initializer_list < int > list) {
   int b = 0;
   for (auto x: list) {
      b += x;
   }
   return b;
}
int main() {
   int y = a({2,4,6,10});
   std::cout << "Result : " << y << std::endl;
   return 0;
}

Output

Output of the above code is as follows −

Result : 22

Combining Two Initializer Lists

Consider the following example, where we are going ti combine values from multiple initializer lists.

#include <iostream>
#include <initializer_list>
#include <vector>
std::vector < int > a(std::initializer_list < int > x, std::initializer_list < int > y) {
   std::vector < int > b;
   b.insert(b.end(), x);
   b.insert(b.end(), y);
   return b;
}
int main() {
   auto b = a({1,3,5}, {2,4,6});
   for (auto value: b) {
      std::cout << value << " ";
   }
   std::cout << std::endl;
   return 0;
}

Output

Following is the output of the above code −

1 3 5 2 4 6