When working with C++, it is common to initialize objects using different syntaxes and constructors. However, C++11 introduced a new feature called uniform initialization. One aspect of this feature is std::initializer_list, which allows us to initialize objects with a list of values in a more concise and flexible way. In this blog post, we will explore how to use std::initializer_list to initialize objects in C++.

What is std::initializer_list?

std::initializer_list is an STL class template that represents a lightweight array-like container. It is designed specifically for initialization purposes and is commonly used with constructors and assignment operators. With std::initializer_list, we can pass multiple values to initialize an object using a simple and readable syntax.

Using std::initializer_list for object initialization

To use std::initializer_list, we need to include the <initializer_list> header. Let’s start by looking at an example using std::initializer_list to initialize a vector of integers:

#include <iostream>
#include <vector>

int main() {
    std::vector<int> numbers = {1, 2, 3, 4, 5};
    
    for (const auto& num : numbers) {
        std::cout << num << " ";
    }
    
    return 0;
}

In the above code, we create a std::vector<int> named numbers and initialize it with a list of integers using std::initializer_list. The syntax {1, 2, 3, 4, 5} represents the initializer list of integers. We can then iterate over the vector and print each element.

The output of this code will be:

1 2 3 4 5

Using std::initializer_list for custom objects

std::initializer_list is not limited to primitive types; it can also be used to initialize objects of custom classes. Let’s look at an example of initializing a car class using std::initializer_list:

#include <iostream>

class Car {
public:
    Car(const std::string& make, const std::string& model)
        : make_(make), model_(model) {}
        
    void PrintInfo() const {
        std::cout << "Make: " << make_ << ", Model: " << model_ << std::endl;
    }
    
private:
    std::string make_;
    std::string model_;
};

int main() {
    Car myCar = {"BMW", "X5"};
    myCar.PrintInfo();
    
    return 0;
}

In this code, we define a Car class with a constructor that takes two parameters: make and model. Using std::initializer_list, we can initialize a Car object named myCar with the values "BMW" and "X5". We then call the PrintInfo() member function to display the make and model of the car.

The output of this code will be:

Make: BMW, Model: X5

Conclusion

Using std::initializer_list in C++ enables us to initialize objects with a clean and concise syntax. It improves code readability and makes object initialization more flexible. Whether it’s initializing containers or custom classes, std::initializer_list is a powerful feature to simplify object initialization in C++.