Held: Thursday, 26 February 2015

Back to Outline 05 - Cron. On to Outline 07 - Debugging with gdb.

Summary

We continue our exploration of C compilation, considering more details of the C preprocessor.

Related Pages

• EBoard (Source) (HTML) (PDF)

Overview

• Including files.
• Macros.
• CPP conditionals.
• Detour: Standard header file format.
• Command-line flags.
• Hack: Generic data types.

Administrivia

• This week's assignment: Write a macro library for ...
• Class next week may be on gdb if I can get Stone to teach it.
• Don't forget this week's CS Table! It should be really interesting.

Including Files

• Useful for headers. (Why?)
• Can include regular code, too. (Why?)
  • E.g., an alternative to separate compilation.

Playing with Macros

• Simplest: Constants. Mostly useful for readability.
• Standard: Alternative to functions.
  • Usually more efficient than function calls.
• But still dangerous if used less carfully.

CPP Conditionals

• Typical use: Different code on different systems.
• Another typical use: Insert code for debugging by printing or whatever.
• Sam sometimes puts unit tests in that way. Your main gets put in an ifdef section.

Detour: Standard Header File Format

• So, why do we write header files in the "standard" format?
• Consider two include files, zebra.h and stripes.h. zebra.h includes stripes.h. What happens?

The Preprocessor and the Command Line

• Can put -Dwhatever
  • Makes it easier to change how you compile your program on the fly.

Some Great Preprocessor Hacks

• Include one file multiple times (with different definitions) to get simlar definitions. (E.g., different kinds of lists.)
• Process the same list multiple times.