Advanced UNIX progamming

1
Advanced UNIX progamming

• Fall 2002
• Instructor Ashok Srinivasan
• Lecture 3

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

• Assignment 1 announced
• Due Sep 13, 2002

3
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

4
UNIX programming environment

• Editors
• C compilers
• Debugger
• Makefiles
• make

5

• 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

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Some useful functions

• include ltstdio.hgt
• int sprintf(char s, const char format, ...)
• int sscanf(const char s, const char format,
  ...)
• How would these be used to get all the fields
  from the output of the shell command ps?
• See example4.c.

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Some Unix System Calls

• You may use these in your first assignement
• system
• mkstemp

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system

• include ltstdlib.hgt
• int system(const char string)
• Works as if string is typed into the shell at a
  terminal
• Returns the exit status (see man page for
  waitpid)
• Usually -1 is returned if there is an error

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mkstemp

• include ltstdlib.hgt
• int mkstemp(char template)
• template should end in XXXXXX
• It replaces XXXXXX with unique file name, and
  returns an open file descriptor for a file
  available for reading and writing