CS 403: Programming Languages

1
CS 403 Programming Languages

• Lecture 4
• Fall 2004
• Department of Computer Science
• University of Alabama
• Joel Jones

2
Outline

• Symbol Tables
• Activation Records
• GDB
• Reading Questions for Next Class

3
Symbol Tables (Cont.)

• A hash table can be added to the previous data
  structure to accelerate the search.
• Elements with the same name are linked from top
  to bottom.
• Search start at the entry of the hash table and
  proceeds through the linked list until the end of
  the list is reached (old_id) or until the link
  list refers to an element below scope_marker(LL -
  1) (new_id)

4
Symbol Tables (Cont.)

• This approach does not work in some cases.
• Consider the with statement of Pascal and Modula
  2.
• Date RECORD day 1..31
• mo month
• yr CARDINAL
• END
• d1 Date
• WITH d1 DO
• day10 moSep yr1981
• END
• is equivalent to
• d1.day10 d1.moSep d1.yr1981

5
Symbol Tables
6
Symbol Tables (Cont.)
7
The binding of referencing environments

• Shallow binding the referencing environment of a
  routine is not created until the subroutine is
  actually called.
• Deep binding the program binds the environment
  at the time the subroutine is passed as a
  parameter.
• Deep binding is implemented by creating an
  explicit representation of a referencing
  environment and bundling it together with a
  reference to the subroutine. Closure

8
Activation Records for Nested Routines
9
GDB

• GDB Gnu DeBugger
• Preparation
• Compile with gcc -g
• Example gcc -g -o myProgram myprogram.c
• Run the program under control of gdb
• Example gdb myProgram

10
MP1

• Complete write-up available on the class website
• Basic Idea write 1 or more programs and
  associated GDB scripts that demonstrate object
  (generic, not OO) lifetimes and scopes
• GDB scripts should print out addresses, values of
  variables, etc.

11
Demonstration of GDB

• Create program
• Compile it
• Run under gdb
• Print some variables
• Show automatically running script
• gdb -x gdbCmdFile myProgram

12
Reading for Next Class

• Skim the following, paying particular attention
  to how to print the addresses of variables
• Debugging with GDB The GNU Source Level Debugger
• http//www.gnu.org/manual/gdb-5.1.1/gdb.html
• GDB Quick Reference Card
• http//www.refcards.com/download/gdb-refcard-lette
  r.pdf