Class 33: Pointers and Arrays

Held: Friday, 29 October 2010

Summary: We continue our exploration of pointers in C. In particular, we consider the relationship between pointers and arrays in C.

Related Pages:

• EBoard.
• Lab: Pointers, Revisited.
• Reading: K&R 5.3-5.4.

Notes:

• We may have propsies today. Yay!
• EC for MD's Monday presentation.
• EC for Saturday's Men's Soccer game.
• EC for LoC truck.
• Reading for Monday: K&R 5.3 and Appendix B.
• Are there questions on Exam 2.

Overview:

• Pointers and Arrays.
• Labs.

Pointers and Arrays

• In C, a pointer and an array are more or less the same (at least internally).
• In fact, you can (mostly) treat a pointer as an array or an array as a pointer.
• Some key differences:
  • When you declare arrays, you usually specify the size.
  • You should not be able to change where an array "points".
• In many ways, arrays are syntactic sugar for pointers.
• For example a[i] is really just *(a + i).

Your Questions

• Can a pointer point to a pointer? If so, can you access the value by using multiple * commands?
• In page 105 about the comparison between the pointers and arrays, what is the difference in the declaration of arrays and pointers?
• Please explain (*t = *s) != '\0'. Thanks very much.
• What is a cast?
• I don't understand what the point of allocp and afree are. Can you just talk about them a little?
• Could you provide some examples in class illustrating the situations where it would be prudent to use pointers in a program?

Labs

• Continue the lab on pointers.
• Begin the lab on pointers, revisited.