C++ Concept Map

Templates

An important form of polymorphism in C++ is the ability to describe a class that has parameters that can specialize its use. A template is a class declaration with one or more parameter names embedded in it that can be replaced at compile-time by an argument.

For instance, part of a class that encapsulates an integer array might be:

class X {
private:
  int array[100];
...
};

The type of the array is fixed. However, by turning the declaration into a template, the class can then be made to contain an array of any type:

template<class T>
class X {
private:
  T array[100];
...
};

This no longer a class declaration, but a template for a family of class declarations. To use the template, the parameter must be instantiated:

X obj1<int>;

makes an object of type X<int>, whereas:

X obj2<float>;

makes an object of type X<float>, and:

X obj2<Y>;

makes an object of type X<Y>, where Y is a previously-defined class.

Global functions can also be templated, e.g.

template<class T, int size>
void process(T a[]) {
  for (int i = 0; i < size; i++)
    a[i] *= 2;
}

Please mail any corrections and/or suggestions to Roger Hartley at
rth@cs.nmsu.edu