In C++, both function overloading and function templates allow us to create functions that can operate on different types of data. While they might seem similar, they are used for different purposes. In this article, we will learn the differences between function overloading and function templates, and understand when to use each.

Function Overloading in C++

Function overloading in C++ allows us to define multiple functions with the same name but with different parameters. The compiler determines which function to call based on the arguments passed to it.

• The functions must have different parameter lists (either in number or type of parameters).
• The return type of the functions can be the same or different.
• The compiler uses the argument types and number to decide which function to invoke.

The parameters should follow any one or more than one of the following conditions for Function overloading:

void functionName(int a);
void functionName(double a);
void functionName(int a, int b);

When to Use Function Overloading in C++?

Use function overloading when you need to perform similar operations on different types or numbers of inputs.

Example

The below example demonstrates how function overloading works in C++.

// C++ program to demonstrate function overloading

#include <iostream>
using namespace std;

// Function to print an integer
void print(int i) { cout << "Integer: " << i << endl; }

// Function to print a double
void print(double f) { cout << "Double: " << f << endl; }

// Function to print a string
void print(string s) { cout << "String: " << s << endl; }

int main()
{
    // Call the print function with an integer argument
    print(10);

    // Call the print function with a double argument
    print(10.5);

    // Call the print function with a string argument
    print("Hello");

    return 0;
}

Integer: 10
Double: 10.5
String: Hello

Time Complexity: O(1) for function call resolution.
Auxiliary Space: O(1)

Function Templates in C++

We use function templates to define a generic function template that can work with any data type. Instead of writing multiple overloaded functions, we simply write a single template function.

• The template keyword is used to define a template.
• T is a placeholder for the data type that will be specified when the function is called.
• The compiler generates the appropriate function definition based on the type of arguments passed.

Syntax:

template <typename T>
void functionName(T a);

template <typename T>
T functionName(T a, T b);

When to Use Function Templates in C++?

Use function templates when you need a single function to work with different data types without rewriting the function for each type.

Example

// C++ program to demonstrate template function usage

#include <iostream>
using namespace std;

// Template function to print values of any type
template <typename T> void print(T value)
{
    // Output the value of the specified type
    cout << "Value: " << value << endl;
}

int main()
{
    // Call the print function with an integer argument
    print(10);

    // Call the print function with a double argument
    print(10.5);

    // Call the print function with a string literal
    // argument
    print("Hello");

    return 0;
}

Value: 10
Value: 10.5
Value: Hello

Time Complexity: O(1) for function template instantiation.
Auxiliary Space: O(1)

To know more about the topic refer to Generics in C++.

Difference Between Function Overloading and Function Templates in C++

The following table illustrates he key differences between function overloading and function templates: