Exploring undefined behavior using constexpr | Hacker News Reader

Exploring undefined behavior using constexpr

shafik.github.io

26 pointsmatt_d7 comments

I’ve recently been writing just pure C and have been surprised by how much I enjoy it. There are so many things about C++ that have remained confusing to me, even though I’ve used it extensively over the years and have a lot of respect for the language. But the simplicity not having to wrap my head around all kinds of bizarre concepts that still confuse me in C++, I must say it’s been a bit liberating of a feeling.

I had the same expirience and I am totally with you. At work we use modern C++ which I enjoy, but I have the same liberating and comfortable feeling when I turn back to my small C projects at home.

But I also think that huge C Projects can turn into a hell easily.

I guess writing it can be fun, but managing it isn't. When I review C code I have to spend 80% of my attention on figuring out if there's anything fishy happening with memory. It's terrible how much C code is just memory-management boilerplate.

This is a super interesting approach I hadn’t thought of. Unfortunately it seems to be limited in practice, as demonstrated by the article: first of all, certain constructs cannot be used in a constexpr context, and second (and more worryingly) many compilers fail to diagnose undefined behavior or do so incorrectly. If the second issue can be fixed I can see this being a very useful, if specialized tool for improving the safety of C++ code.

> certain constructs cannot be used in a constexpr context

yet. endgame is to make mostly everything constexpr-able. constexpr dynamic_cast, try/catch, and virtuals are coming in C++20 for instance and there are papers to get constexpr memory allocations in C++23.

> many compilers fail to diagnose undefined behavior or do so incorrectly.

It would be much easier if undefined behaviour was better defined, because then a compiler could recognize it and diagnose it. Of course then it wouldn't be undefined behaviour any more, so problem solved.

The bounds of what consists undefined behavior is, well, defined. The “undefined” bit refers to the behavior in this case, not its ability to be recognized.

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