Parameterized includes

Question

In a few C programs (for example in gecko) I've noticed an idiom whereby a program will temporarily define a macro, then include a file which uses that macro, then undefine the macro. Here's a trivial example:

speak.c:

#define SPEAK(phrase) (printf("When I speak I say %s\n", (phrase)))
#include "dog.h"
#undef SPEAK

dog.h:

SPEAK("woof");

Which expands to:

(printf("When I speak I say %s\n", ("woof")))

I gather this might be a useful technique to generalize included code by being able to specify behavior at the expansion site.

Does this pattern have a name, or has it been written about previously?

Pretty strange to use non-compiling code as an example, there's no `;` after the statement (and a statement in `()` makes little sense to me). — unwind, Dec 06 '17 at 14:32
This is close/identical to the [X macro](https://en.wikipedia.org/wiki/X_Macro) concept. — Oliver Charlesworth, Dec 06 '17 at 14:32
Possible duplicate of [What is a good reference documenting patterns of use of X-Macros in C (or possibly C++)?](https://stackoverflow.com/questions/264269/what-is-a-good-reference-documenting-patterns-of-use-of-x-macros-in-c-or-possib), and there's also [Real-world use of X-Macros](https://stackoverflow.com/questions/6635851/real-world-use-of-x-macros) — underscore_d, Dec 06 '17 at 14:36

score 4 · Accepted Answer · answered Dec 06 '17 at 14:36

4

This is a variant of what are often called X macros.

Parameterized includes

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