Question

I was reading Stroustrup’s c++ FAQ and I noticed that, at one point, he had a writeonly qualifier in the language. After some discussion, a colleague and I could only come up with one purpose – side effects, specifically in the case of some memory mapped IO. Is there any other legitimate usage for a writeonly qualifier?

Answer 1

The write-only qualifier would be useful for hardware registers since reading from a write-only register would lead to undefined behavior or subtle run-time errors. You can use a #define such as #define write-only and then apply this to a register like, special_register write_only UTXBUF;

There is a blog post at EE Times on How to Enforce write-only access.