Recitation%20Week%203

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Recitation Week 3

• Object Oriented Programming
• COP3330 / CGS5409

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Todays Recitation

• Compiling with g
• Using Makefiles
• Debugging

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Compiling C / C programs with gcc g

• The base command for the Gnu C compiler is "gcc"
• The base command for the Gnu C compiler is "g"

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Single File Programs

• To compile a program that is in a single file,
  the easiest compilation uses the command format
• g ltfilenamegt
• Where the filename ends with ".cpp
• Example
• g prog1.cpp

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Multiple File Programs

• To invoke the Compile stage, which translates
  source code (.cpp files) into object code (.o
  files), use the -c flag. Format
• g -c ltfilenamegt
• To name a target (something other than the
  default filename, use the -o flag. Format
• g -o lttarget_namegt ltremainder of commandgt

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Multiple File Examples

• g -o yadda.o -c fraction.cpp
• This command invokes just the compile stage on
  fraction.cpp, but names the object code file
  "yadda.o" (instead of the default "fraction.o").
• g -o bob.exe circle.o main.o
• This command links the two object code files
  ("circle.o" and "main.o") into an executable,
  called "bob.exe" (instead of the default
  "a.out").
• g -o myProgram thing.cpp main.cpp
• This command compiles and links (since -c not
  used) the code files "thing.cpp" and "main.cpp"
  together into the executable program called
  "myProgram".

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Reminders

• Source code is just text!
• For the purposes of assignments, ANY text editor
  can be used to
• Practice with at least one Unix text editor
  create code files
• For unix beginners, "pico" is recommended, due to
  easy learning curve.
• Emacs, Vim, MUCH more powerful

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CS Account login

• Understand how to log into both CS machines
• linprog.cs.fsu.edu
• program.cs.fsu.edu
• Use SSH (Secure SHell) client to login
• Files created on a windows machine can be FTP-ed
  to CS accounts with the SFTP feature built into
  the SSH software

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SSH / SCP

• Usage
• sftp username_at_hostname
• get filename - retrieve remote file
• put filename - upload local file
• Standard Unix commands
• cd, ls, pwd, chmod, rename, rm, mkdir, rmdir,
  help, quit
• Alternatively, GUI File Managers
• WinSCP - Free Windows client with SFTP capability
  
• FileZilla - Open source cross-platform GUI client

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Makefiles

• Unix system has what is called a make utility
• Configuration file to assist with compilation
• Simple text file, should be named either
  makefile or Makefile

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Makefiles

• Idea of the target
• What is able to be made?
• Dependency list
• What needs to be re-made each time?
• Command list, and formatting
• i.e. it must be preceded by a single tab
  character
• Extra targets, like clean, for cleanup
• target that lists a cleanup command (like the
  remove rm command)
• More than one target
• placing a target like all at the top, and
  listing the executables made by the file as the
  dependency list

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Sample Makefile

• This is a comment line
• Sample makefile for fraction class
• frac main.o frac.o
• g -o frac main.o frac.o
• main.o main.cpp frac.h
• g -c main.cpp
• frac.o frac.cpp frac.h
• g -c frac.cpp
• clean
• rm .o frac

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Sample Makefile

• frac main.o frac.o
• g -o frac main.o frac.o
• Specifies frac as the target
• Depends on main.o and frac.o
• If either of these files changed since the last
  build, then frac must be rebuilt
• Links two object code files together into a
  target executable called frac

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Sample Makefile

• main.o main.cpp frac.h
• g -c main.cpp
• Specifies how to built the target main.o
• Depends on main.cpp and frac.h
• If either file changes, main.o must be rebuilt
• Uses normal g commands for the compile stage

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Sample Makefile

• Any section can be invoked specifically with the
  command
• make lttarget_namegt
• For instance, to build only the frac.o target,
  use
• make frac.o

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Sample Makefile

• clean
• rm .o frac
• The target name is clean
• Executes the remove command (rm)
• Removes the object code file(s) and the
  executable(s) from the current directory

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Types of Errors

• Compilation errors -- usually syntax errors,
  undeclared variables and functions, improper
  function calls.
• Linker errors -- usually involve undefined
  functions or multiply-defined functions or
  symbols
• Run-time errors -- two varieties.
• Fatal -- cause program to crash during execution
• Non-fatal (or logical) -- don't crash the
  program, but produce erroneous results.

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Error Reporting

• Compile stage errors  These are errors that will
  be reported by the compiler, which usually
  provides a filename and line number indicating
  where it ran into trouble, for each error
  reported.
• Linking stage errors These errors, also reported
  by the compiler, do not usually contain line
  numbers, since the linker works on object code,
  not on the original source code.
• Run-time errors  These must be tested while
  running a fully-compiled program.

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Debugging Compile Stage Errors

• Always start at the top of the list of errors.
  Fix the first error, then recompile and see what
  is left.
• If a list of errors is too long, compile and
  debug one file at a time.
• When searching for an error, start with the
  indicated line number, but also look in the
  vicinity (usually previous lines) for the
  possible error.
• Compile portions of programs as you go -- don't
  wait until the program is fully written to do the
  first compile!

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Debugging Linking Stage Errors

• Learn what kinds of problems cause linker errors
  (usually problems with agreement between
  definitions and calls).
• Linker errors usually specify some kind of symbol
  (used by the compiler), which often resembles a
  function or variable name. This is usually a good
  clue.
• Learn about good compilation techniques and
  pre-processor directives that help avoid linker
  errors.

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Debugging Compile Stage Errors

• To catch fatal errors, try to wedge the mistake
  between extra printout statements to locate the
  cause.
• To catch logic errors, place extra printout
  statements in code while testing (to be removed
  in the finished version). Especially, print out
  values of internal variables to locate
  computation problems.

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Questions?