Class 31: Pointers

Held: Tuesday, 26 October 2010

Summary: We study pointers, one of the important data types in C.

Related Pages:

• EBoard.
• Lab: Pointers.
• Reading: K&R 5.1-5.2.

Notes:

• Cool Theatre stuff on campus this week.
• Reading for tomorrow: K&R 5.3-5.4.
• Don't forget questions!
• LoC Truck on Friday.
• We'll go over some questions and issues on HW6.

Overview:

• Your Questions.
• Lab.

Memory and Pointers

• Everything (or at least every variable) has to be stored somewhere in memory.
• The program needs to know where it's stored.
• In C, you can access information about where things are stored.
  • In Scheme (at least standard Scheme), you cannot.
• The address-of operation (&) tells you where in memory that thing is stored.
• An address is also called a pointer.
• The type of a pointer is specified by the type of the thing pointed to, followed by a *. So int * means a pointer to an integer.
• You can find the contents of something pointed to by prefixing the pointer with *.

Your Questions

• Couldn't you also return the new a and b instead of making swap a void function?
• In the swap routine example, are pointers the only way to make that function work?
• I thought the main advantage in using pointers is to decrease the use of memory, but I don't see that in the examples. Why do we need pointers?
• Could you explain the * operator? It seems clearly laid out on page 94, but I'm just not wrapping my head all the way around it.

Lab

• Do The Lab.
• Be prepared to reflect.