CSC161 2010F, Class 30: Make, Revisited

Overview:
* About Make.
* Your Questions.
* A Collaborative Makefile.

Admin:
* NO LAB TODAY!
* I hope you had a great break.
* Who saw "The Social Network" and its evil portrayal of CS?
* Returned: HW5, Exam 1.  
  * Sorry for the delay.
  * That's all I'm grading until HW6 and Exam2.
* I got more responses for today's reading.  Thanks.  
  Some of you asked enough questions that I probably did not need everyone's.
* Reading for Tuesday: K&R 5.1 and 5.2.
* Are there questions on Assignment 6?

Assignment 6

* For the Fibonacci sequence, can we use the general formula?
  * Sure, if you think it works correctly.
  * You should try to avoid computing the sequence recursively
* Bring more questions tomorrow!

Make

* A long-standing and widely-used Unix tool for managing "builds"
  * You describe the steps necessary to create something (an application,
    a document, whatever)
  * You describe dependencies
  * Make figures out the ordering
* One person can describe the structure of building, others can create
  the parts involved in the building
* Makefiles includes:
  * Variable definitions
  * Rules 
TARGET: PREREQUISITES
        INSTRUCTIONS
  * Comments
  * A few other notational conveniences
* In most Unix projects, you will see that Makefiles include the following
  targets:
  * default: Whatever is most important (could be a list of options)
  * all: all the programs/documents/whatever
  * test: test the programs
  * install: put the program/documents where they belong (not in this
    class)
  * clean: Clean up after yourself
  * package: Build the tarball
* Four kinds of variables used in Makefiles
  * Ones the user designs herself
  * Ones expected by the system that the user might decide to customize
    * CFLAGS
    * LDLIBS
    * ...
  * Ones provided as part of the standard make packagew
    $(CC) - our C compiler
    $(COMPILE.c) - our C compiler with flags
  * Automatic variables: Ones that make your life easier
    $@ - the target
    $< - the first prerequisite
    $^ - all the prereqs
    $? - prereqs that are newer than the target
    $* - is the prefix of the target

Your Questions

* Is make basically a new language we need to learn?
  * Yes, but it's fairly simple (or at least what you will use)

C-related questions
* I need some review of what .o files are for. 
  * Partially compiled C files
  * Three step compiling process
    * Preprocess (from .c to .cpp)
    * Translate to object code (from .cpp to .o)
    * Link together .o files to the executable
  * Basically, .o files are expensive to produce, but not so expensive
    to link, so we try not to rebuild them if not necesssary
* I don't know what -I DIRECTORY does, exactly.  
  * Tells the compiler where to look for #include "foo.h"
* Generally, I don't understand most of this stuff about libraries.  Why are they necessary?  
  * Saves computing time to build, encourages reuse
  * For now, we jsut use .o files as our libraries
* Can we talk a bit more about CFLAGS and similar things?
  * Instructions to the C compiler.
  * -Wall - warn me about stupid code
  * -g - set up for the debugger
  * -O - make it run fast, but maybe not look so much like the original
  * -I dirs - where to look for include files
  * -lm - Use the Math library
  * I'll teach you other important ones as they come along
  * -lex (not correct) - Use lex library

Linux-related questions
* What is a 'jar'? - A collection of compiled Java programs
* Is a lexer a program that is assumed to be built for the implementation of this program, or is it some automatic file that is generated, or what? 
  * A library that says "When I see this pattern, do this thing"
* What does flex do?
  * Builds the C code from a simple syntax
* What does this mean: <q>First, we setup our experiment by creating an empty yacc source file and registering with RCSusing ci (that is, we want a version-controlled yacc source file)</q>
  * Not all translation is easy - Yacc is a tool for doing "parsing"
  * Version-control - A sensible way to keep lots of versions of a file
    around so that multiple people can work on it
* What is bison and what does it do?
  * The successor to yacc.  It builds parsers.
* Does the suffix .y signify anything specific?
  * It's a yacc/bison file
* What is an 'awk' filter?
  * A cool text processing language

Make
* I still don't quite understand $(...)
  * How you say "Include the value of this variable"
* I noticed that the text used a "rm" command in the makefile - does this mean we can use any valid terminal command in our makefile rules?
  * Yes, that's the idea
* I'm a little bit confused about phony targets, though. Because they don't represent files, are phony targets kind of like functions? 
  * Basically, meta-instructions
* I was wondering if you might be able to show us how to use wildcards in our makefiles.
* How does this work?
prog: *.c
        $(CC) -o $@ $^