Templates in C++

By: Rajesh P.S.

Templates in C++ are a great tool of technology enabling classes and functions to be described in a very general form. They allow conceptualization of data types as variables with place holders for empty spaces and creation of different functions and classes with a possibility to use them across different sections of the code. Prototypes are the ones giving the opportunity to write the code which can be perfectly adapted to work with different data types without having to retype the same logic over and over, thus making the principle of generic programming fundamental for C++.

How do templates work in C++?

Templates in C++ work by allowing the definition of generic functions and classes with placeholders for data types. When a template function or class is instantiated with specific data types, the C++ compiler generates specialized code for those types. This process is called template specialization. Templates enable code reusability and type flexibility, making it possible to write a single function or class that can work with different data types, while the compiler generates the appropriate type-specific versions during compilation, ensuring efficient and type-safe code.

Types of Templates in C++

In C++, there are primarily two types of templates: function templates and class templates.

Function Templates

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Function templates in C++ are a powerful feature that allows the creation of generic functions. They are defined with a placeholder type parameter, often denoted as <typename T> or <class T> , which represents an unspecified data type. When a function template is called with specific data types, the C++ compiler generates specialized versions of the function for those types, ensuring that the function can work with a variety of data types without requiring separate implementations for each. Function templates are invaluable for writing reusable algorithms, libraries, and containers that need to operate on diverse data types while maintaining type safety and code efficiency.

Creating and using function templates in C++ allows you to write generic functions that can work with different data types. Here are the steps for creating and using function templates, along with an example:

Define a Function Template

Use the template keyword to declare a function template. Specify the template parameter using <typename T> or <class T> , where T is the placeholder for the data type.

template <typename T> T myMax(T a, T b) { return (a > b) ? a : b; }

Use the Function Template

To use the function template, call it by providing specific data types within angle brackets ( <> ) or let the compiler deduce the data types automatically.

int result1 = myMax(5, 10); // Compiler deduces data types double result2 = myMax(3.14, 2.71);

Compile and Run

The compiler generates specialized versions of the function for the data types used during the function calls.

Full Source

#include <iostream> template <typename T> T myMax(T a, T b) { return (a > b) ? a : b; } int main() { int result1 = myMax(5, 10); // Compiler deduces int data type double result2 = myMax(3.14, 2.71); // Compiler deduces double data type std::cout << "Maximum (int): " << result1 << std::endl; std::cout << "Maximum (double): " << result2 << std::endl; return 0; }

//Output: Maximum (int): 10 Maximum (double): 3.14

In this example, the function template myMax is defined with the template parameter T, allowing it to work with various data types. The compiler deduces the appropriate data type for each function call, ensuring type-safe and efficient code.

Class templates

Class templates in C++ are a mechanism for defining generic classes with placeholder type parameters. These type parameters, often represented as <typename T> or <class T> , allow the creation of classes that can work with a variety of data types. When a class template is instantiated with specific data types, the C++ compiler generates specialized versions of the class, enabling the creation of objects of those types. Class templates are essential for building flexible and reusable data structures, containers, and libraries that can accommodate different data types while ensuring type safety and code efficiency through template specialization.

Creating and using class templates in C++ allows you to define generic classes that can work with different data types. Here are the steps for creating and using class templates, along with an example:

Define a Class Template

Use the template keyword to declare a class template. Specify the template parameter using <typename T> or <class T> , where T is the placeholder for the data type.

template <typename T> class MyArray { private: T* data; int size; public: MyArray(int size); T& operator[](int index); ~MyArray(); }; template <typename T> MyArray<T>::MyArray(int size) { this->size = size; data = new T[size]; } template <typename T> T& MyArray<T>::operator[](int index) { if (index < 0 index >= size) throw std::out_of_range("Index out of bounds"); return data[index]; } template <typename T> MyArray<T>::~MyArray() { delete[] data; }

Use the Class Template

To use the class template, instantiate it with specific data types within angle brackets ( <> ). You can create objects of the templated class with different data types.

MyArray<int> intArray(5); // Creates an array of integers MyArray<double> doubleArray(3); // Creates an array of doubles

Compile and Run

The compiler generates specialized versions of the class for the data types used during instantiation.

Full Source

#include <iostream> #include <stdexcept> template <typename T> class MyArray { private: T* data; int size; public: MyArray(int size); T& operator[](int index); ~MyArray(); }; template <typename T> MyArray<T>::MyArray(int size) { this->size = size; data = new T[size]; } template <typename T> T& MyArray<T>::operator[](int index) { if (index < 0 index >= size) throw std::out_of_range("Index out of bounds"); return data[index]; } template <typename T> MyArray<T>::~MyArray() { delete[] data; } int main() { MyArray<int> intArray(5); for (int i = 0; i < 5; i++) { intArray[i] = i * 2; } MyArray<double> doubleArray(3); for (int i = 0; i < 3; i++) { doubleArray[i] = 1.5 * i; } for (int i = 0; i < 5; i++) { std::cout << "intArray[" << i << "] = " << intArray[i] << std::endl; } for (int i = 0; i < 3; i++) { std::cout << "doubleArray[" << i << "] = " << doubleArray[i] << std::endl; } return 0; }

//Output: intArray[0] = 0 intArray[1] = 2 intArray[2] = 4 intArray[3] = 6 intArray[4] = 8 doubleArray[0] = 0 doubleArray[1] = 1.5 doubleArray[2] = 3

In this example, the class template MyArray is defined, and two objects of the templated class are created—one for integers and one for doubles. The code demonstrates how to use the class template to create dynamic arrays of different data types and access their elements safely.

Overloading of Template Function in C++

Overloading template functions in C++ involves defining multiple functions with the same name but different template parameters or argument lists. This allows you to provide specialized implementations for different data types or configurations.

Define the Template Function

Create a template function that serves as the base for overloading. It can have one or more template parameters.

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

Overload the Template Function

Create additional functions with the same name but different template parameters or argument lists. These functions should specialize the behavior for specific cases.

// Overload 1: Specialized for strings template <> std::string myFunction(std::string value) { return "String: " + value; } // Overload 2: Specialized for integers template <> int myFunction(int value) { return 2 * value; }

Use the Overloaded Template Functions

Call the overloaded template functions with specific data types or configurations.

std::string strResult = myFunction("Hello"); // Calls the string specialization int intResult = myFunction(5); // Calls the int specialization

Full Source

#include <iostream> #include <string> template <typename T> T myFunction(T value) { return value; } // Overload 1: Specialized for strings template <> std::string myFunction(std::string value) { return "String: " + value; } // Overload 2: Specialized for integers template <> int myFunction(int value) { return 2 * value; } int main() { std::string strResult = myFunction("Hello"); // Calls the string specialization int intResult = myFunction(5); // Calls the int specialization std::cout << strResult << std::endl; // Output: "String: Hello" std::cout << intResult << std::endl; // Output: 10 return 0; }

In this example, we have overloaded the myFunction template function for both strings and integers. The specialized overloads provide different behavior for these data types.

Overloaded template functions are called based on the best match for the provided arguments, ensuring that the appropriate version is invoked for a given data type. This technique is valuable for providing tailored behavior for various data types while maintaining code flexibility.

Function Overloading VS. Templates in C++

Function overloading in C++ allows multiple functions with the same name in a single scope, but with different argument lists or types. It's typically used to provide different implementations for specific parameter variations. On the other hand, templates allow you to define generic functions or classes that work with a range of data types without specifying them explicitly. Templates are parametrized by type and are instantiated at compile-time, enabling code reusability and adaptability to various data types, making them more versatile for generic programming than function overloading. While function overloading deals with different signatures for the same function name, templates are focused on writing code that is generic and type-agnostic.

Advantages of Using Templates in C++

Using templates in C++ offers several advantages. They promote code reusability by allowing the creation of generic functions and classes that can work with different data types, reducing the need for redundant code. Templates provide type safety by performing compile-time type checking, helping catch errors early in development. They lead to more efficient code since the compiler generates specialized versions of templates for each data type, resulting in optimized execution. Additionally, templates facilitate generic programming, enabling the development of flexible and adaptable libraries and algorithms that can be applied to a wide range of scenarios, making them a powerful tool for building robust and versatile C++ applications.

Conclusion

Templates in C++ are a feature that allows the creation of generic functions and classes with placeholder types, enabling code to work with various data types without duplication. They provide type safety, code reusability, and efficient code generation by allowing the compiler to generate specialized versions for different data types, making them a fundamental tool for generic programming in C++. Templates offer flexibility and adaptability, making C++ code more versatile and maintainable.

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