CSC 282.01, Class 01: Introduction

Overview

• Preliminaries
  • Notes and news
  • Upcoming work
  • Questions
• The origins of the course.
• Course policies
• Some principles and practices.
• Example: C from K & R
• Detour: A C memory problem
• Exercise: Some simple tasks

News / Etc.

• Welcome to “Thinking in C and *nix”.
  • The course has had a variety of titles.
  • I’ll use at least one more, but I’ll explain more later.
• I’m Sam (or SamR)
• I’ll take attendance, mostly to make sure that I know everyone’s name.
• Please sign up for a Github account and send me your username.
• As seems to be the norm in this department, I’m putting together a series of readings for this course. They are definitely “a work in progress”. Nonetheless, I’d like you to read the drafts.

Upcoming Work

• Read: the introductory material
• Read: Raymond, chapter 1
• Do: Simple tasks
• Do: *nix tools

Good things to do

• Lots of fun dance things this weekend.
• Go to Macalester and watch the swimmers swim and the divers dive.

Questions

The origins of the course.

• Sam was teaching compilers.
• Students were clueless about key issues in C and Unix, like Macros and Make and other things that start with ‘Ma’.
• Sam now teaches them.

Course policies and procedures

• S/D/F course
  • Attend at least 11/13 classes
  • Be active in class when you attend
  • Do the readings
  • Try the homework (timebox)
• 1 credit course. At least three hours per week on the course.
  • 1 hour in class.
  • 30 minutes reading.
  • 90 minutes programming.
  • 2000 minutes dealing with annoying software that doesn’t work correctly (optional)
• I will often spend class time talking through assignments (and make you talk through them)
• I will generally call on people randomly.

Some principles and practices.

• Testing is important! Find ways to test. (Automated.)
• Code style is important! We will use the GNU C standards.
• Have fun with what you are doing!
• Automate when possible!
• Write general code.

Example: C from K & R

char *
fun (char *t, char *s)
{
  while (*t++ = *s++)
    ;
  return t;
} // fun

What does this do?

• Keeps doing something until some error comes up. Then returns t.
• It’s a lot like strcpy
• *t = *s assigns a character.
• Issue: What about size.
• The ++ moves on to the next character. (Use, ++ is pointer increment.)
• We are incrementing before we use it.
• = returns the value assigned. When we hit '\0', it stops.
• That’s the end of string character.

Reflections on the world view this code represents

• You know the underlying representation of data.
• You know about pointers.
• You like to be concise.
• You assume that the client is smart enough to pass in the correct parameters (e.g., that there’s enough space).

Questions

• Is there a preconditions that strlen(t) >= strlen(s)?
  • No! We need to know how much data is associated with t, not the length of the current string associated with t.
  • char *target = malloc(123);
• Why don’t the programmers check the preconditions?
  • It is costly to check, and they want to be efficient. Let’s assume our clients are competent, even though that is tradtionally a bad assumption.
  • If they are worried about the preconditions, but also being efficient, they could use assert or put code in a #ifndef NDEBUG block.
  • C does not provide a mechanism for checking how much memory is associated with a pointer.
• What would you choose as the preconditions?
  • There is enough memory associated with t (or you want to do some stupid array overflow for nefarious means)

Detour: A C memory problem

Exercise: Some simple tasks