Ivor Horton's Beginning Visual C++ 2012

FUNCTION TEMPLATES

The last example was somewhat tedious in that you had to repeat essentially the same code for each function, but with different variable and parameter types. However, there is a way of avoiding this. You have the possibility of creating a recipe that will enable the compiler to automatically generate functions with various parameter types. The code defining the recipe for generating a particular group of functions is called a function template.

A function template has one or more type parameters, and you generate a particular function by supplying a concrete type argument for each of the template’s parameters. Thus, the functions generated by a function template all have the same basic code, but customized by the type arguments that you supply. You can see how this works in practice by defining a function template for the function max() in the previous example.

Using a Function Template

You can define a template for the function max() as follows:

template<class T> T max(T x[], const int& len)
{
   T maximum(x[0]);
   for(int i = 1; i < len; i++)
      if(maximum < x[i])
         maximum = x[i];
   return maximum;
}

The template keyword identifies this as a template definition. The angled brackets following the template keyword enclose the type parameters that are used to create a particular instance of the function separated by commas; in this instance, you have just one type parameter, T. The class keyword before the T indicates that the T is the type parameter for this template, ...