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Implementing not-quite-namespaces in C

Hi, all!

A few days ago i came across a trick in C. It isn’t new, but i hadn’t seen it used quite this way before and i wanted to share it…

Background: i have several mini-libraries which i tend to copy directly in to other projects. It has happened that i then use two other libraries together, and both of them internally use the same underlying mini-library. In some cases i want each to continue to use their own copy (maybe a different/incompatible version), but not collide with the other copy. Here’s one way to do it…

In the lib’s main header, before we declare any of its API:

#if !defined(MY_NS)
#  define MY_NS(X) my_namespace_prefix_ ## X
#endif

We then declare our types and functions using that macro:

int MY_NS(func1)( ... );
struct MY_NS(type1) { ... };

And throughout the implementation and client code we use:

int x = MY_NS(func1)( ... );

Each library which wants to import and rename the API then simply has to redefine MY_NS while building the included mini-library.

The major down-side is that this construct makes reading the docs through tools like doxygen more difficult.

Happy hacking!