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Templates allow writing generic code in C++. Through templates, we can define functions or classes that operate on generic type parameters, letting the compiler generate the actual code for the specific types requested.

Defining a Function Template

To define a function template, we precede the function definition with the template keyword, followed by the list of type parameters enclosed in angle brackets <>. Commonly, typename or class is used to declare a generic type.

// T is the generic type parameter
template <typename T>
T add(T a, T b) {
    return a + b;
}

Function Call and Template Argument Deduction

When we call the function, we can explicitly specify the type in angle brackets:

int res1 = add<int>(5, 10);
double res2 = add<double>(3.14, 2.71);

However, the C++ compiler is usually able to deduce the type automatically from the passed input parameters (Template Argument Deduction):

int res1 = add(5, 10); // The compiler deduces that T is int

Try it yourself