With the introduction of C++11, variadic templates became a powerful feature that allows programmers to write functions and classes that accept a variable number of arguments. This is especially useful when dealing with containers of unknown or varying sizes, such as vectors or tuples. In this blog post, we’ll explore variadic templates and see how they can be used to write more flexible and reusable code in modern C++.

What are Variadic Templates?

Variadic templates are a feature in C++ that allow us to define functions and classes that can accept any number of arguments of any type. The syntax for declaring a variadic template is simple:

template <typename... Args>

The ellipsis (...) indicates that a varying number of arguments can be passed to the template.

Using Variadic Templates

Once we have defined a variadic template, we can use it to declare function templates or class templates. Let’s see how we can use variadic templates to create a simple print function that can accept any number of arguments and print them to the console:

#include <iostream>

template <typename T>
void print(T value) {
    std::cout << value << std::endl;
}

template <typename T, typename... Args>
void print(T value, Args... args) {
    std::cout << value << " ";
    print(args...);
}

In this example, we have defined two overload functions for print(). The first overload handles the case when only one argument is passed, and simply prints it to the console. The second overload takes multiple arguments and prints each one followed by a space. It then recursively calls itself with the remaining arguments until all arguments have been printed.

Variadic Template Expansion

To expand the arguments in a variadic template, we can use a technique called “parameter pack expansion”. This allows us to access each argument individually and perform operations on them. In the print() function example above, we use the args... parameter pack expansion to recursively call print() for each remaining argument.

We can also use parameter pack expansion to perform other operations, such as passing each argument to another function or storing them in a container. The possibilities are endless, and variadic templates provide a flexible way to work with a varying number of arguments.

Conclusion

Variadic templates are a powerful feature in modern C++ that allow us to write functions and classes that can accept a varying number of arguments. They provide a flexible and reusable way to work with containers of unknown or varying sizes. By leveraging parameter pack expansion, we can perform operations on each argument individually. Variadic templates are an essential tool in any C++ programmer’s toolkit and enable us to write more expressive and efficient code.

#cpp #variadictemplates