Class 04: The Basics

Held Monday, January 31, 2000

Overview

Today's outline does not yet have an overview. Please let me know if you think it should have one.

Notes

• Some of you have asked about context switches. A context switch occurs when computation switches from one process to another (or from one thread of computation to another). That is, one computation is interrupted and another starts (or resumes). When you switch context, you must save the state of the current computation (registers, sometimes the stack, etc.) and then restore them when the thread resumes.
• I expect that Wednesday will be a laboratory, but we'll see.

Contents

• A Quick Introduction to C
• Sockets in C, Continued

Summary

A Quick Introduction to C

• I don't remember all the history of C. What I remember is that it was created at Bell labs as a language for writing operatins systems (for Vaxen, if I'm not incorrect).
  • For efficiency, it has a lot of operations that are easy to translate into assembly code.
  • It is somewhat higher-level than assembly code (but not much).
  • It is concise (for programmer efficiency).
• You can't really program in C without understanding pointers, so we'll spend a significant time on pointers.
• In general, you compile C files with

  % gcc -c filename.c
  

• This produces a .o file. You then need to link together the .o files along with the libraries. (Java dynamically loads libraries; C does not.)

  % gcc -o excecutable file1.o ... filen.o
  

• Note that almost every C library function can be accessed through the man command. So you can type man perror to understand perror.
  • We may use man while trying to understand the sample code.

Sockets in C, Continued

• We continue our introduction to C by studying the rest of the simple socket example.
• Before reading that example, we should see what it does.
  • Make a copy of client.c and server.c.
  • gcc -c client.c
  • gcc -o client client.c
  • gcc -c server.c
  • gcc -o server server.c
  • server
  • (In another window): client hostname