Week 7 Notes for DAT2330 - Ian Allen
Supplement to Text, outlining the material done in class and lab.

Remember - knowing how to find out the answer is more important than
memorizing the answer.  Learn to fish!  RTFM![*]

([*] Read The Fine Manual)

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Miscellaneous Notes
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Unscrambling a terminal that is in graphics characters set mode:
- if what you are typing appears as line drawing characters instead of
  letters
- this might happen after you accidentally use "cat" to send a
  non-text file to your terminal screen, e.g. cat /bin/ls
- To Fix:
  - On Floppix type:  setterm -reset
  - On ACADAIX type:  reset
  - On either type:   echo ^V^O     (that's CTRL-V CTRL-O)

GNU - Gnu's Not Unix
- Free Software Foundation (FSF) project
- rewrite Unix in the public domain (the way it started out)
- chief architect: Richard Stallman (original author of EMACS)

Linux distribution == Linux Kernel + GNU Utilities
- The GNU kernel hasn't progressed far  (named HURD)
- So, we use the Linux kernel with all the GNU utility software

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Building C Language Programs
----------------------------

Text - Chapter 14 - p.541-545

Understanding Unix "compile, link, and stop".

gcc vs cc
- vendors started selling the C compiler "cc" separately to make money
- many shops now use the free (CopyLeft) GNU C Compiler: gcc
- Floppix is too small to have either compiler
- ACADAIX only has "cc"
- NETSRV (Solaris) only has "gcc"
- Regular Linux distributions come with "gcc"

"cc" and "gcc" are "front-ends" to the compiler and linker
- if you supply source files (*.c), the compiler will be used
- if you supply object files (*.o), the linker will be used
- if you supply both, both will be used

What does the linker name the output of the link step?
- a.out

When do you type "a.out" and when do you type "./a.out"?
- when you have or don't have the current directory in your PATH
- don't put the current directory in your PATH; it's a security risk
 
Understand: Figure 14-2:
  Read the first part of "Compiling and Linking a C Program"
- Preprocessor
  Input: Text files: Your source code
  Output: Text files: Source code with macros and header files expanded
     and included
- Compiler
  Input: Text files: Source code with macros and header files expanded
     and included
  Output: Text files: Assembly-language symbolic source code for your
     processor
- Assembler
  Input: Text files: Assembly-language symbolic source code for your
     processor
  Output: Object files: Binary, machine-readable instructions for your
     processor
- Linker
  Input: Object files (including ones taken from system libraries)
  Output: one Binary: An executable, machine-language program
     containing everything needed to execute.

Understand: Figure 14-3:
    Dependency Graph for building a program from source.

    foo -> foo.o -> foo.c

Which parts of the process produce which kinds of error messages?
- preprocessor
  - if you mis-spell a file name on the command line
  - if you mis-spell an #include name
  - if you use an unknown #-directive
- compiler
  - if you leave off a semicolon or mis-match parentheses
  - if you have undeclared variables
  - most other syntax errors
- linker
  - if you use an unknown library function (mis-spelling?)
  - if you declare two external objects with the same name
    - e.g. two global functions with the same name

cc and gcc
- The -c option tells the compiler to stop once the *.o is built
  - don't call the linker
  - the name of the *.o is taken from the *.c source file
- The -o option is used to change the default name of the output file
  - to have the linker change "a.out" to something reasonable
  
make
- "make" is a Unix program that reads a text Makefile and builds things
  - things are usually programs, but could be anything
- the first thing in the Makefile is the thing being made
  - usually this is the name of the binary we are building
- Makefile is built from dependencies and commands
  - dependencies are read by the make command, not by the SHELL
  - each command line starts with a TAB character
  - each command line is passed to the SHELL for execution

Sample Makefile:

    # This is a sample Makefile to build foo from source.
    # idallen@ncf.ca

    foo: foo.o
    ___TAB___ cc -o foo foo.o

    foo.o: foo.c
    ___TAB___ cc -c foo.c

Another Sample Makefile:

    # This is a sample Makefile to build dog from source.
    # idallen@ncf.ca

    dog: cat.o
    ___TAB___ cc -o dog cat.o

    cat.o: cat.c
    ___TAB___ cc -c cat.c

(See the text for another example.)