Assignment 4

• Write a data safe library offering the following functionality:
  • Calling data_safe(ds_register, 0, 0) will return a unique random key (a positive integer). Use rand() to generate random numbers (and man rand to find out how).
  • Calling data_safe(ds_store, key, value) will store the value (a positive integer) in the data safe (under the key). It should return the value if everything worked, -1 otherwise (e.g. if there is no space left)
  • Calling data_safe(ds_retrieve, key, n) will retrieve the nth value stored under the key, or -1 if less then n values have been stored under the key
  • Calling data_safe(ds_delete, key, 0) will delete all entries stored under key (you may then reuse key for future register calls, as long as you still generate a random key)
  • Make sure that at least 100 keys can be in use in parallel, and that at least 10000 data items can be stored in total
• Make sure that the data is not accessible in any other way (using legal C)
• Implement the libray in its own source file, with a header file data_safe.h that contains all necessary declarations
• Write a main program ds_test.c that uses the library, storing 10 values under 3 different keys, retrieving them and delete them. Use a reasonably varied sequence of storage, retrieval, and registration
• Hints:
  • Use static local variables to store the necessary data in the data_safe() function
  • Use preprocessor #define statements to define the symbolic constants ds_register, ds_store,...
  • Be careful to avoid handing a key already in use out on registration. Carefully design your data structures first, the operations will be simple to implement
  • Don't be too concerned about efficiency!