Templates in C++

Introduction

• In C++, templates are a powerful feature that allows for generic programming. 

Definition

• Templates are a powerful feature in C++ that provides generality, type safety, compile-time polymorphism, efficiency, template specialization, and template metaprogramming.
• A template is a code construct that enables the definition of a parameterized type or function that can operate on different data types without having to write duplicate code for each type.
• A template acts as a blueprint for functions or classes, where the data type is specified later when the function or class is used.

Characteristics

• Templates are a powerful feature that provides a way to write generic code that can work with any/different data type, making them highly flexible and reusable.
• Templates are used extensively in the C++ Standard Template Library (STL) to provide a wide range of generic algorithms and data structures, such as containers like vector, set, and map.
• Templates are essentially blueprints that can be used to generate code for a specific data type at compile-time, i.e., we can write code that works for any data type, without having to specify each data type we want to work with manually.
• Templates are essentially a way to parameterize types, functions, and classes so that they can be used with any data type, instead of just a fixed set of types.
• Templates provide a way to ensure data type safety in C++ programs, i.e., by using templates, we can ensure that a function or class only works with the correct data types, preventing errors and bugs.
• Templates support compile-time polymorphism, meaning the correct code is generated during compilation rather than at runtime. The actual implementation of a template function or class is generated at compile time, based on the data types used in the program.
• Templates can be used to write highly optimized code that is tailored to specific data types. By using templates, we can write code that is optimized for the specific data types used in our program, leading to better performance.
• Templates can be used for metaprogramming, which involves writing code that generates code at compile time. This can be used to perform complex computations or generate complex data structures at compile time, leading to more efficient code.

Syntax

(i) The syntax of a function template is

template <typename T> return_type function_name(parameters);

Here, T represents a generic data type that will be replaced by an actual data type when the function is called.

(ii) The syntax of a class template is 

template <typename T> class ClassName { members };

Here, T is used as a placeholder for the data type of class members.

In C++, the keyword typename can also be replaced with the keyword class, and both have the same meaning in template syntax.

Type of Templates

• There are two main types of templates in C++:-

  • Function templates

    • A function template allows a single function definition to work with different data types.
      The compiler generates the appropriate function code for each data type used.
    • A function template is a generic function that can be used with different types of parameters.
    • We can write a single function that works with any data type with templates.
    • We can declare a function template using the “template” keyword, followed by a list of template parameters enclosed in angle brackets.

  • Class templates

    • A class template allows a class to operate with generic data types.
    • The compiler creates a specific class definition when the template is instantiated with a particular data type.
    • A class template is a generic class that can be used with different types of data members and member functions.
    • The class template is defined using the “template” keyword, followed by a list of template parameters enclosed in angle brackets.

Use of Templates

• There are many use cases for templates, including:-
  • Templates are commonly used to implement container classes such as vectors, lists, maps, and sets. These classes are designed to hold collections of data of any type, and templates provide a way to write a single implementation that works for all data types.
  • Templates can be used to write generic algorithms that work with any data type. For example, the “sort” function in the standard library is a template function that can be used to sort arrays of any data type.
  • Templates are an essential tool for generic programming in C++. Generic programming involves writing code that can work with any data type, allowing for more flexible and reusable code.
  • Templates provide a way to ensure type safety in C++ programs. By using templates, we can ensure that a function or class only works with the correct data types, preventing errors and bugs.
  • Templates can be used to write highly optimized code that is tailored to specific data types. By using templates, you can write code that is optimized for the specific data types used in our program, leading to better performance.
  • We can also use templates to create generic classes, allowing us to write code that works with any data type.
  • Templates are a powerful tool in C++ that enables us to write flexible, efficient, and reusable code that is both efficient and flexible.
  • They also help reduce code duplication and make programs more efficient.