CSC 282.01, Class 10: More Fun with Macros

Overview

• Preliminaries
  • Notes and news
  • Upcoming work
  • Questions
• Lab!

News / Etc.

• Sorry that the assignment come out too late. This one will be more timely.

Upcoming work

• Homework: Something involving uthash.h or <sys/queue.h>

Good things to do

• 11am Faculty Governance Discussions
• 11am-1pm Spark Tank presentations
• CS Extras at 4:15
• James McBride at 4:15ish
• Movie at 5 at Strand
• Director talk at 6:30 pm JRC 101 free pizza
• Some famous guy giving multimedia talk on Politics of Masculinity 7pm Harris
• Music faculty performance 7:30 pm in Sebring-Lewis
• Godspell is 7:30 pm at Loft (sold out)
• James McBride and his band 8:00 pm in Herrick

Questions

Review

• Macros are awesome - Text substitution is your friend
  • Common Lisp Macros are better than C macros
  • Scheme Macros may eventually be hygenic, which is even better
• Great for logging/testing
  • Use assert
  • Write our own custom version of assert
• Useful for writing DRY code

Detour: assert

• It’s a macro.
• You can see how it is defined in /usr/include/assert.h
• Note: Consider the following

assert (sqrt(4) == 2);

This normally gets expanded to some strange code like

if (! (sqrt(4) == 2)) { fprintf (stderr, ...); exit(0); };

You can turn off assert with -DNDEBUG. If we just define assert(X) as nothing, we get

;

Two approaches

#ifdef NDEBUG
#define assert(X) (void (0))
#define assert(X) do { } while (0)
#endif

Detour: Why do we use the do ... while(0)

• Some random Stackoverflow page at http://stackoverflow.com/questions/1067226/c-multi-line-macro-do-while0-vs-scope-block reminds me that we consume the semicolon for multi-statment macros because it’s necessary for an if

if (test)
  MACRO(stuff);
else
  other_stuff();

Lab

Clone https://github.com/Grinnell-CSC282/macros-2017S

Write a simple test program for stacks of int values.