Classes

In our previous simple examples, we can note a difference between first class data types such as int and second class data types such as the string type char *. For example, we cannot assign character constants directly to a character string outside of a declaration, and instead must use operations like strcpy; the string representation makes an assumption that the final character of every string is the NIL character $\backslash 0$, but the manipulations allowed on the data structure do not ensure this. Further, the character array does not know how many characters have been allocated to it. It is easy to walk off the end of the array and attempt to write into invalid memory locations. C-style strings cannot be used for template-sorting algorithms since the comparison operator ``<'' compares the values of the pointers, not the contents of the string.

What we would like to have is a better string which behaves much as an int, or a float. C++ provides the ability to extend the language features in this fashion through the use of classes. Classes can be thought of as object definitions where each object encapsulates a set of data and a number of routines defined to provide transparent access to the objects behavior.