Templates

Templates allow writing generic code that can work with different data types without duplicating the code for each specific type.

Variables

template <typename T>
T pi = T(3.1415926535897932385);

std::cout << pi<float>; // Specifies that T is float

Functions

template <typename T> // Generic type T
T add(T a, T b) {
    return a + b;
}
 
template <typename T, typename I> // Generic types T and I
T multiply(T a, I b) {
    return a * b;
}

The type can be explicitly specified or deduced from the arguments:

int x = add<int>(5, 10); // Specifies that T is int
double y = add(3.5, 2.5); // T is automatically deduced as double
 
int z = multiply<int, float>(4, 5.5); // Specifies that T is int and I is float
double w = multiply(2.5, 3); // T is deduced as double

Classes

template <typename T = int> // Generic type T with default value int
class Box {
    T value;
 
public:
    Box(T value) : value(value) {}
    T getValue() {
        return value;
    }
};

Box<float> floatBox(123.5); // Specifies that T is float
std::cout << floatBox.getValue(); // Prints 123
 
Box<> defaultBox(42); // Uses the default int value for T
std::cout << defaultBox.getValue(); // Prints 42

Next: Containers Iterators and Algorithms