Class 29: Macros

Held: Friday, 15 October 2010

Summary: We consider ways in which to use the C preprocessor, particularly in the use of macros.

Related Pages:

• EBoard.
• Lab: Macros and the C Preprocessor.
• Reading: K&R 4.11.

Notes:

• For the Monday after break, please read Chapters 1 and 2 of the Make Book.
• I got way too few questions on the reading.
• Homework for Wednesday after break will be posted in a few days.
• Have a great break!

Overview:

• Using the Preprocessor.
• Your Questions.
• Macros and the C Preprocessor.

Basics

• The C preprocessor processes a variety of simple directives, such as #include, #define and such.
• Run the C preprocessor with cc -E file.c
• The output goes to standard out, so you may want to read through it with less

Your Questions

When making #include statements with quotation marks, if the mentioned file isn't found in the working directory, will the compiler look for it in the same directory as the standard C libraries? I felt like the reading implied this but I wanted to be sure.

If it's not in the working directory, then the C compiler will issue an error.

What are are the arcane rules for nested uses of ##?

I don't think there are any. Concatenation can happen left-to-right or right-to-left.

Lab

• Do the lab.