CS 3733 Operating Systems, Fall 2006 Assignment 0 Comments

1. Explain in your own words what a NULL pointer and a null byte are.
   A NULL pointer is a pointer and a null byte is a char. A null byte has the value 0. A NULL pointer is not of integer type. If you cast the integer 0 to a pointer, you get a NULL pointer. If you cast a NULL pointer to an intger the result is system dependent.
2. What is the size of each?
   The size of the NULL pointer is system dependent, but is usually 4 or 8 bytes.
   The size of a null byte is 1.
3. How are they used?
   A NULL pointer is used to represent a pointer that does not point to anything. It is sometimes used as a return value to indicate that an error occurred and sometimes used for initializing pointers before they have anything to point to. Often is it used to represent the end of a list of pointers, possibly a linked list or an array.
4. Explain in words why the data type for an array of strings as described above has data type char **.
   A string has data type char * which is a pointer to a char. An array of these has data type char ** which is a pointer to a char *.
5. Suppose you want to have a function create one of these arrays of pointers and return it in a parameter, rather than as a return value. What data type would be passed as this parameter?
   char *** as in makeargv.