Advanced UNIX progamming

1
Advanced UNIX progamming

• Fall 2002
• Instructor Ashok Srinivasan
• Lecture 2

Class web site http//www.cs.fsu.edu/asriniva/co
urses/aup-02
Acknowledgements The syllabus and power point
presentations are modified versions of those by
T. Baker and X. Yuan
2
Announcements

• Collected your quizzes
• The grade on this will not count towards your
  course grade
• However, it will provide you feedback on your C
  knowledge
• You can try the linked list question at home
• You should be able to write the code within 15
  minutes, without referring to any book
• You should have received an email from me, if you
  are registered for this course

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Week 1 Topics

• Course outline and policies
• UNIX programming environment
• Editors
• C compilers and debuggers
• Makefiles
• Review some features of C
• Header files
• Command line arguments
• Utilities
• Review some UNIX system calls
• system, etc

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UNIX programming environment

• Editors
• C compilers
• Debugger
• Makefiles
• make

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Editors

• vi, pico, emacs, etc
• What is good about emacs?
• emacs is more than just an editor
• You can compile and edit within emacs
• If you know lisp, you can expand its
  functionality
• Some useful commands to get started
• C-h t get tutorial
• C-g cancel command
• C-x C-c quit emacs
• C-h help

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etags

• This helps you go to a function definition
• Particularly useful in programs spanning multiple
  files
• At the shell prompt, type
• etags .ch
• In emacs
• Choose visit tags from the _C_ menu
• Or ESC-x visit-tags-table
• Subsequently, find tag from the menu, or ESC-.,
  will take you to the function definition

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Compiling in emacs

• Choose compile from the _C_ menu
• Or ESC-x compile
• Errors and warnings will be printed on a
  sub-window
• CTL-X will take you to the next error or
  warning

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C compilers

• gcc, cc
• Using ANSI C, the code must pass with flags
• Wall ansi pedantic
• with no warning messages
• See example1.c
• How can we fix warning?
• Some examples
• gcc g Wall ansi pedantic example1.c
• gcc g c Wall ansi pedantic example1.c
• gcc g example1.o
• gcc g example.o -lm

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Debugger

• ddd, xxgdb, gdb
• The code must be compiled with g option.
• The power of a debugger
• Finding the line that causes core dump
• See example1.c
• Break point, show value, change value, step,
  next, continue, print
• Very efficient in debugging sequential code
• Not very effective in debugging concurrent code
  (multiple threads, multiple processes)
• Good software development practice You must have
  seen each line of your code execute in the
  debugger, at least once

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• run ltcommand line argumentsgt to run the program

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Make

• make -f makefileoption target
• A tool to update files derived from other files
• The default files for make are ./makefile,
  ./Makefile, ./s.makefile
• Use the f option to specify some other file
• make f makefile1
• The makefile has three components
• Macros define constants
• Target rules Specify how targets are made
• Inference rules Specify how targets can be made,
  implicitly. make will first check if a target
  rule applies, before using inference rules.

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make ... continued

• Macros
• String1 string2.
• Example
• CCgcc
• CFLAG-Wall ansi pedantic
• Target rules
• Target prerequisite
• lttabgt command
• lttabgt command
• Example
• a.out myprog1.c myprog2.c myprog3.c
  (CC) (CFLAG) myprog1.c myprog2.c
  myprog3.c

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make ... continued

• Inference rules
• Target
• lttabgt command
• lttabgt command
• Target must be of the form .s1 or .s1.s2 where
  .s1 and .s2 must be prerequisites of the
  .SUFFIXES special target.
• .s1.s2 ? make .s2 from .s1
• .s1 ? make from .s1
• Example
• .c
• (CC) o _at_ lt
• .c.o
• (CC) c lt

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makefile examples

• See the example makefiles
• makefile, makefile1, makefile2
• makefile1 will recompile only the modified files,
  instead of everything
• makefile2 has inference rules
• www.cs.fsu.edu/cgi-bin/man.cgi can be used to
  find more information

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Review some features of C

• Header files
• Macros
• Command line arguments
• Utilities

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Header files

• Usually define interfaces between separately
  compiled modules
• May contain macro definitions, preprocessor
  directives, declarations of types, and function
  prototypes
• Should not contain variable definitions or
  executable code

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Some header file errors

• Improper header file use can cause problems
• Try compiling example2.c
• Including a header file multiple times may cause
  redefinition errors
• Why does including stdio.h twice not cause any
  problem?
• Look at /usr/include/stdio.h

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Conditional Code in Headers

• Preprocessor directives are used to prevent the
  body of a header file from being used multiple
  times.
• ifndef MYHEADER
• define MYHEADER
• / the body of the header file /
• endif

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Macros with and without Parameters

• define MAX_LENGTH 256
• ... for (i 0 i lt MAX_LENGTH i) ...
• Macros can have parameters
• define max(a,b) (a gt b) ? a b
• What is wrong with the following?
• define sum(a, b) a b
• define product(a, b) ab
• See example3.c, example3b.c, example3c.c, and
  example3d.c