1. ENEE150 – 0102 ANDREW GOFFIN Abstract Data Types

2. ADT Basics All about designing a data type that others can use easily! Two parts  A set of data (struct)  Operations on that data (methods) Separation between use and implementation  We’re concerned with the implementation of ADTs For Java programmers, very similar to classes  Small aside, OOP design principles are not enforced by the C language, we must enforce them ourselves Goffin – ENEE150

3. Why use ADTs? The separation of use and implementation increases portability of code  Example: Complex Number ADT  One person will write the data type, but ANY other programmers can use the data type in their code!  Simple as a declaration of any other primitive (int, float, char, double) data type Goffin – ENEE150

4. ADT Implementation Use a struct to group together the data stored by the ADT typedef struct complex_type{ float real; float imag; } complex; Declare “operations” using function prototypes Goffin – ENEE150

5. ADT Operations Public operations/functions can be called by the user of the ADT  Such as constructor and destructor Private operations/functions can only be used in the implementation of an ADT  The compiler should not let the user call these functions Goffin – ENEE150

6. Encapsulation Place struct and public function prototypes in header file Public function implementation and private functions go into.c file of same name as header  You can explicitly make private functions private with the “static” keyword – static functions cannot be called in another.c file Ex: static int foo();  Same goes with global variables Goffin – ENEE150

7. Polymorphism If you want to treat the type of an ADT’s data as a variable, you need a slightly different approach. Two (main) approaches in C:  Unions  Generic Pointers Goffin – ENEE150

8. Unions Single variable which can take on a fixed number of data types union val{ int ival; float fval; char cval; } x; Stores only one value, but can be any of the declared data types  Access each particular data type with ‘.’ syntax, like structs Goffin – ENEE150

9. Generic Pointers Pointers that can point to any kind of data  declared with “void *” Can be set to an endless number of types that don’t have to be specified by the implementation  More powerful than unions in this sense That said, you need to cast the relevant information to a “void *” explicitly