Index

1. Introduction to the command line

• in this module we will examine:
  • tools necessary to develop game engines: gdb , emacs and friends
• examine how one can integrate Python into a game engine doom3
• examine and extend a small physics game engine and expose its API to Python
• also revisit C and familiarise ourselves with pointers and indirect function calls
• learn how to debug shared libraries and exploit remote debugging

2. Introduction to the Command line

• in this lecture series we will be using GNU/Linux to develop our understanding of programming in C
• one of the beauties of GNU/Linux is that you can do all your development from the command line or alternatively from a graphical interface
  • on GNU/Linux the command line interface is extremely powerful
  • once learnt it will last you a lifetime
  • different GUI's and IDE's come and go

3. GNU/Linux at South Wales

• you can create yourself a username at South Wales by clicking here
  • the same link can be used to change your password, or reset your password if you forget it
• all machines in J109 are triple boot (will boot into GNU/Linux, OSX or Windows) we will be using GNU/Linux

4. Introduction to the Command line

• make sure that you have a working username and password under GNU/Linux and boot up the imac into Linux
• and login
• and open up a terminal window
• adjust the window font size so it looks good and rearrange the window and this browser so both fit on the same screen without overlaps

5. Introduction to the command line

• the first command to be aware of is man . To examine what this does type:

• $ man man

• when you have read enough, type ' q '
• to find out whether a command exists for a particular function, type

• $ man -k directory

• this command tells you all the commands which are associated with directories
• you can filter the search by:

• $ man -k directory | grep list

6. Critical general purpose command line programs

• cd change directory
• pwd print working directory
• cp copy a file
• mv rename a file (move)
• cat display contents of a file
• less display contents of a file, a page at a time
• grep print lines matching a pattern
• all programs can be combined using the pipe operator
• for example

• $ man -k directory | less

7. Critical development command line programs

• gcc the C GNU compiler
• gdb the GNU debugger
• emacs the GNU editor

8. File organisation

• please try and keep your $HOME directories tidy
  • it is good practice to create separate directories for different courses and tutorials
• for example, here we might want to use the following commands:

• $ mkdir -p cs3s609/tutorial1
  $ cd cs3s609/tutorial1

• (before moving onto the next slide)
  

9. Minimal introduction to emacs

• to start editing the file tiny.c with emacs editor type:

• $ emacs tiny.c

• critical key commands
  • this editor can be controlled from the keyboard (without the mouse)
• use cursor keys, page up, page down, to move around the text
• in this section of the notes the notation ^C means press the control key and then press the C key, finally release both keys
• type ^X^S to save your file
• type ^X^C to quit emacs
  

10. Creating a simple C program under GNU/Linux

• using emacs create the following file (called tiny.c )
• the contents of this tiny.c should be as follows

• #include <stdio.h>
  
  main()
  {
      int i;
  
  
      for (i=1; i<=12; i++) {
          printf(‘‘%d x 8 = %d\n'', i, i*8);
      }
  }

11. Minimal introduction to GCC

• gcc is the GNU C compiler
• now exit emacs and compiler tiny.c , you can compile and link tiny.c like this:

• $ gcc -g tiny.c

• this generates a file a.out which can be run, from the command line by typing:

• $ ./a.out

12. Minimal introduction to GDB

• gdb is the GNU debugger, which can be useful to both
  • debug your program
  • understand how a program works
• for example, suppose we wanted to understand which lines of code are executed in your tiny.c program, you could

• $ gdb a.out
  GNU gdb 6.4.90-debian
  Copyright (C) 2006 Free Software Foundation, Inc.
  GDB is free software, etc
  (gdb) break main
  Breakpoint 1 at 0x8048365: file tiny.c, line 7.
  (gdb) run

• Breakpoint 1, main () at tiny.c:7
  7        for (i=1; i<=12; i++) {
  (gdb) next
  8            printf(‘‘%d x 8 = %d\n'', i, i*8);
  (gdb) next
  1 x 8 = 8
  7        for (i=1; i<=12; i++) {
  (gdb) next
  8            printf(‘‘%d x 8 = %d\n'', i, i*8);
  (gdb) print i
  $1 = 2
  (gdb) next
  2 x 8 = 16
  7        for (i=1; i<=12; i++) {
  (gdb) quit
  The program is running.  Exit anyway? (y or n) y

13. Extending tiny.c to use a function

• use emacs to modify the tiny.c program (to include a mistake)

• #include <stdio.h>
  
  int mult (int i)
  {
      return i*9;
  }
  
  main()
  {
      int i;
  
  
      for (i=1; i<=12; i++) {
          printf(‘‘%d x 8 = %d\n'', i, mult(i));
      }
  }

• now recompile the program by:

• $ gcc -g tiny.c

• and run the program, as before

• $ ./a.out
  1 x 8 = 9
  2 x 8 = 18
  3 x 8 = 27
  4 x 8 = 36
  5 x 8 = 45
  6 x 8 = 54
  7 x 8 = 63
  8 x 8 = 72
  9 x 8 = 81
  10 x 8 = 90
  11 x 8 = 99
  12 x 8 = 108

• we can single step the program to find out where the mistake occurred

• $ gdb a.out
  GNU gdb 6.4.90-debian
  Copyright (C) 2006 Free Software Foundation, Inc.
  GDB is free software, etc
  (gdb) break main
  Breakpoint 1 at 0x8048365: file tiny.c, line 7.
  (gdb) run

• (gdb) run
  Starting program: a.out
  
  
  Breakpoint 1, main () at tiny2.c:12
  12       for (i=1; i<=12; i++) {
  (gdb) step
  13           printf(‘‘%d x 8 = %d\n'', i, mult(i));
  (gdb) step
  mult (i=1) at tiny2.c:5
  5        return i*9;
  (gdb) fin
  Run till exit from #0  mult (i=1) at tiny2.c:5
  0x08048388 in main () at tiny2.c:13
  13           printf(‘‘%d x 8 = %d\n'', i, mult(i));
  Value returned is $1 = 9

• at this point we see our mistake, the function has returned 9
• we can see this again if we continue around the for loop

• (gdb) step
  1 x 8 = 9
  12       for (i=1; i<=12; i++) {
  (gdb) step
  13           printf(‘‘%d x 8 = %d\n'', i, mult(i));
  (gdb) step
  mult (i=2) at tiny2.c:5
  5        return i*9;

• (gdb) print i
  $1 = 2
  (gdb) up
  #1  0x08048388 in main () at tiny2.c:13
  13           printf(‘‘%d x 8 = %d\n'', i, mult(i));
  (gdb) print i
  $2 = 2
  (gdb) down
  #0  mult (i=2) at tiny2.c:5
  5        return i*9;

14. Using gdb from within emacs

• you can run gdb from within emacs and have emacs perform source file correspondence
• if you wish to do this then it would be sensible to create a file .gdbinit and populate it with

• #
  #  this file is the gdb start up script and
  #  you can place any gdb commands in here
  #
  break main
  run

• this file is read by gdb when gdb is executed
• now at the command line, you can type:

• $ emacs

• at this point make sure your emacs is a large window
• now type: <alt>xgdb<enter> within emacs
• now type: <alt>xgdb-many-windows<enter>
• now you can enter the gdb commands step next print fin and quit and emacs will track the source file, line number, local variables, call frames, output in alternate windows
  • do not resize emacs after this though
    

15. Tutorial

• work though these lecture notes, trying each example in turn

16. References/Further reading

• Introduction to the command line (pdf)
• gdb documentation

Index

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