In C++, templates are a powerful feature that allows us to write generic code. However, when it comes to implementing algorithms that can work with an arbitrary number of arguments, variadic templates come to the rescue.

Introduction to Variadic Templates

Variadic templates allow us to define functions or classes that can take a varying number of arguments of different types. This flexibility enables us to write generic algorithms that can work with any number and type of arguments.

Example - Summing a Variable Number of Integers

Let’s start by implementing a simple algorithm that sums a variable number of integers using variadic templates. Here’s how it can be done:

template <typename T>
T sum(T value)
{
    return value;
}

template <typename T, typename... Args>
T sum(T value, Args... args)
{
    return value + sum(args...);
}

In the above code, we have two template functions: sum() and sum() with variadic arguments. The first function acts as the base case, taking a single argument and returning it unchanged. The second function recursively sums the arguments by adding the current value with the sum of the remaining arguments.

Here’s how you can use the sum() function:

int result = sum(1, 2, 3, 4, 5);  // result = 15

Example - Printing a Variable Number of Values

Now, let’s implement another example where we want to print a variable number of values using variadic templates:

void print()
{
    std::cout << std::endl;
}

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

In this example, we have a base case print() function that simply prints a newline character. The variadic template function print() recursively prints the current value and then calls itself with the remaining arguments.

Here’s how you can use the print() function:

print("Hello", "World", 42);  // Output: Hello World 42

Conclusion

Variadic templates provide a powerful tool for implementing generic algorithms that can work with a varying number of arguments. By utilizing variadic templates, you can write cleaner and more flexible code that can handle a wide range of input combinations.