2.4 Methods

Next, we need to define the methods:

collection ConsCollection( int max_items, int item_size );
void AddToCollection( collection c, void *item );
void DeleteFromCollection( collection c, void *item );
void *FindInCollection( collection c, void *key );  

Note that we are using a number of C "hacks" here. C - even in ANSI standard form - is not exactly the safest programming language in the sense of the support it provides for the engineering of quality software. However, its portability and extreme popularity mean that it is a practical choice for even large software engineering projects. Unfortunately, C++, because it is based on C, isn't much better. Java, the latest fad in the software industry, shows some evidence that its designers have learned from experience (or actually read some of the literature in programming language research!) and has eliminated some of the more dangerous features of C.

Just as we defined our collection object as a pointer to a structure, we assume that the object which belong in this collection are themselves represented by pointers to data structures. Hence in AddToCollection, itemvoid *. In ANSI C, void * will match any pointer - thus AddToCollection may be used to add any object to our collection. Similarly, key in FindInCollection is typed void *, as the key which is used to find any item in the collection may itself be some object. FindInCollection returns a pointer to the item which matches key, so it also has the type void *. The use of void * here highlights one of the deficiencies of C: it doesn't provide the capability to create generic objects, cf the ability to define generic packages in Ada or templates in C++.

Note there are various other "hacks" to overcome C's limitations in this area. One uses the pre-processor. You might like to try to work out an alternative approach and try to convince your tutor that it's better than the one set out here!