C++ Templates

C++ Templates

Templates let you write a function or class that works with different data types.

They help avoid repeating code and make programs more flexible.

C++ Function Templates

You can create a function template by using the template keyword:

Syntax

template <typename T>
return_type function_name(T parameter) {
  // code
}

• T is a placeholder for a data type (like int, float, etc.).
• You can use any name instead of T, but T is common.

Example

template <typename T>
T add(T a, T b) {
  return a + b;
}

int main() {
  cout << add<int>(5, 3) << "\n";
  cout << add<double>(2.5, 1.5) << "\n";
  return 0;
}

In the example above, add<int>(5, 3) tells the compiler to use int for T, while add<double>(2.5, 1.5) tells it to use double.

C++ Class Templates

You can also use templates to make classes that work with any data type:

Syntax

template <typename T>
class ClassName {
  // members and methods using T
};

The example below defines a template class Box that can store and display a value of any data type, and then creates one box for an int and one for a string:

Example

template <typename T>
class Box {
  public:
    T value;
    Box(T v) {
      value = v;
    }
    void show() {
      cout << "Value: " << value << "\n";
    }
};

int main() {
  Box<int> intBox(50);
  Box<string> strBox("Hello");

  intBox.show();
  strBox.show();
  return 0;
}

And this example defines a template class Pair that stores two values of different types and displays them, then creates one pair for a person's name and age, and another for an ID and score:

Example

template <typename T1, typename T2>
class Pair {
  public:

T1 first;
    T2 second;

    Pair(T1
a, T2 b) {
      first = a;

second = b;
    }

    void display()
{
      cout << "First: " << first << ", Second:
" << second << "\n";
    }
};

int main() {
  Pair<string, int>
person("John", 30);
  Pair<int, double> score(51, 9.5);

person.display();
  score.display();

  return 0;
}

Why Use Templates?

Templates let you:

• Avoid repeating the same logic for different types
• Write cleaner, reusable code
• Support generic programming

Note: Templates must be defined in the same file where they are used (usually in the .h file).