Ted: Add link to Jens Gustedt Wordpress article on Empty Macro Detection

2026-05-27T22:00:30Z

Add link to Jens Gustedt Wordpress article on Empty Macro Detection

Ted: Amend opening paragraph

2026-05-27T21:46:21Z

Amend opening paragraph

Ted: Create local page for C preprocessor macros

2026-05-27T21:42:30Z

Create local page for C preprocessor macros

New page

Macros - C Preprocessor Macro language

Some general and comprehensive discussions of C macros can be found at:

# https://home.cs.colorado.edu/~main/cs1300/doc/gnu/cpp_1.html
# https://stackoverflow.com/questions/4674480/do-whilefalse-pattern<br />
# https://www.mikeash.com/pyblog/friday-qa-2010-12-31-c-macro-tips-and-tricks.html<br />
# https://en.wikipedia.org/wiki/C_preprocessor#X-Macros<br />
# https://en.wikipedia.org/wiki/X_macro<br />

=== [[#top|^]] do while(0) ===

Articles on the use of C language 'do while(0)' construct in macros. The do while(0) construct is the only C syntax which expands correctly from C macros regardless of the use of curly braces and semicolons around the given macro.

* https://hownot2code.wordpress.com/2016/12/05/do-while-0-in-macros/

=== [[#top|^]] stringification macro pair ===

A useful macro pair, and this must be a macro pair, is the following set of defines. These defines will accept a string and put double quotes around it:

#define TO_QUOTE_STRING(string) #string
#define WRAPPER_TO_QUOTE_STRING(token) TO_QUOTE_STRING(string)

Guy Rutenberg explains this C pre-processor pattern:
<ul>
* https://www.guyrutenberg.com/2008/12/20/expanding-macros-into-string-constants-in-c/
</ul>

The core rule at play is that C preprocessor does not expand macros preceded by the `#` preprocessor directive, the directive to quote a token. By creating a wrapping macro which does not call the `#` directive, the argument to the wrapper is expanded and then passed to the quoting directive.

=== [[#top|^]] fallthrough macro ===

The `__fallthrough()` macro appears to be a C++ macro. It may be found among Zephyr RTOS 3.4.0 source tree contents. An article on the concept of "fall through" in C switch statements:

* https://www.quora.com/What-is-the-fall-through-behavior-in-C-programming-languages-switch-case-statements

=== [[#top|^]] X macro idiom ===

X macros in C, a pattern involving nested macros makes use of nesting an initially declared and not defined macro within another macro. Danilafe and Phillip Trudeau offer the following blog posts on this topic:

* https://danilafe.com/blog/chapel_x_macros/
* https://philliptrudeau.com/blog/x-macro

Macro tips and idioms:

* https://github.com/pfultz2/Cloak/wiki/C-Preprocessor-tricks,-tips,-and-idioms

=== [[#top|^]] FOREACH macro implementations (may not be fully possible) ===

* https://dev.to/sgf4/foreach-macro-in-c-48ic

* https://dev.to/sgf4/repeat-macro-in-c-2hh0

Macro examples from Zephyr RTOS release 3.7.1:

```
./include/zephyr/devicetree.h:4527:#define DT_INST_FOREACH_STATUS_OKAY(fn) \
./include/zephyr/devicetree.h:4544:#define DT_INST_FOREACH_STATUS_OKAY_VARGS(fn, ...) \
```

=== [[#top|^]] CONTAINER_OF macro ===

Helpful blogpost by Radek Pazdera, full-stack software engineer based in London . . .

* https://radek.io/posts/magical-container_of-macro/

See also 2026 Q1 local page on [[developers|developers]].

=== [[#top|^]] To use GCC to see macro expansion ===

Here is an example shell script which invokes gcc on a single C source file, and causes only the preprocessor to execute. This results in a display of all preprocessor macros:

<pre>
#!/bin/bash

# References:
# * https://gcc.gnu.org/onlinedocs/gcc-3.2.2/cpp/Search-Path.html

# $workspace/zephyr/subsys/testsuite/include/zephyr/fff.h

gcc -E \
-I../../../../../zephyr/subsys/testsuite/include \
-I../../../../../zephyr/include \
./unit-test-mocked-functions.h

exit $?
</pre>

← Older revision		Revision as of 21:46, 27 May 2026
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	Macros - C Preprocessor Macro language		Macros - C Preprocessor Macro language
		+
		+	C's preprocessor language is an important feature and tool in the development space of C language projects. This local wiki page captures some references to preprocessor macro language.
		+
		+	== [[#top\|^]] General Articles about Macros ==

	Some general and comprehensive discussions of C macros can be found at:		Some general and comprehensive discussions of C macros can be found at:

@@ Line 62: / Line 62: @@
 ./include/zephyr/devicetree.h:4544:#define DT_INST_FOREACH_STATUS_OKAY_VARGS(fn, ...) \
 ```
 === [[#top|^]] CONTAINER_OF macro ===

Macros - Revision history

Ted: Add link to Jens Gustedt Wordpress article on Empty Macro Detection

Ted: Amend opening paragraph

Ted: Create local page for C preprocessor macros