What is a constructor?

Objects are complete, miniature programs and, like any good programs, have well defined initialization and termination phases. They have special routines (i.e. member functions ) to look after this. The initialization routine is called the constructor, and C++ ensures that every object is properly initialized by calling its constructor. The designer of the object can have more than one constructor, a situation called overloading and then the compiler will select between them depending on exactly what arguments are passed to the constructor function. However there must always be a default constructor, to be used when no information is supplied.