I wrote this after repeatedly seeing experienced C programmers hit the same sharp edges while moving into modern C++ codebases.

Many of these differences are intentional and defensible from the C++ side. But some are still surprising because they invalidate patterns that were historically common, performant, or idiomatic in C.

The interesting part to me isn’t "C vs C++," but where the languages diverged philosophically: object lifetime vs raw storage, stronger type systems, implicit conversions, ABI and optimization assumptions, and the boundary between "portable" and "works on my compiler."

I’d also be curious which C constructs people still genuinely miss in modern C++. For me, restrict is still near the top of the list.

You might be interested in the scpptool feature to help convert C code to a subset of C that will also compile as C++ (under clang++ at least) [1]. While many of the necessary modifications are fairly trivial, some of them aren't completely so. For example, C++ does not allow `goto`s that would skip over the declaration/initialization of a variable that would be accessible after the jump. So getting the C code to work as C++ can involve some (automatic) code restructuring.

Another annoying detail is that C++ doesn't seem to like forward references of `enum`s. That is, while

    struct A* a_ptr;

    enum A* a_ptr;

One arguable benefit of keeping your C code compatible with (or at least convertible to) C++, is that you can theoretically use scpptool's auto-translation feature as build step to produce memory-safe executables from C code via transpilation to a memory-safe subset of C++.

[1] https://github.com/duneroadrunner/SaferCPlusPlus-AutoTransla...

The "stronger type system" is mostly a myth in my opinion. It was true in the past in pre-prototype C. The void pointer rules are better in C IMHO as they avoid unneeded casts (that then remove more type safety) and FAMs and variably-modified types can express things C++ simply can't do well.

> isn’t "C vs C++,"

Perhaps be more careful in trying to make LLM output look like you wrote it yourself. The incongruent punctuation mark types, with curly apostrophes and straight double quotes mixed together in the same text, are a dead giveaway.

Not sure if you're aware, but defer is proposed for C2Y [1]. It's already available in Clang behind a compiler flag. It is interesting how the languages continue to diverge.

[1] https://www.open-std.org/JTC1/SC22/WG14/www/docs/n3734.pdf

I appreciate that restrict isn't there, because it is yet another UB source, programmer knows not to do errors kind of attitude, and secondly no one seems to care enough to write a language proposal for it.

About half of them read as "I tried to use C++ as a worse C" e.g. using struct initilisation instead of constructors, using malloc instead of new or new[].

My pet peeve with C++ is that the sequence point operator can be overloaded at which point it stops being a sequence point.

> I wrote this after repeatedly seeing experienced C programmers hit the same sharp edges while moving into modern C++ codebases.

...I've seen this more often in the opposite direction. Since C++ is stuck with a ca 1995 non-standard subset of C, C++ coders usually have a very outdated view of C.

> I’d also be curious which C constructs people still genuinely miss in modern C++.

Not implementing the full C99 designated init feature set was a huge missed opportunity in C++20. Every single feature of C99 designated init is important and clicks with the other features and the rest of the language, take one or two away and it becomes mostly useless (e.g. the order requirement in C++20 means that designated init is only useful for trvial structs).

It's especially tragic because Clang already had the full C99 designated init feature set in C++ mode implemented long before C++20 and it worked just fine.

> The interesting part to me isn’t "C vs C++," but where the languages diverged philosophically

IMHO this "schism" was completely unnecessary and only happened because of ignorance and hubris by the C++ designers. Objective-C shows that C can be extended with radical new features but without messing up the "C side" (e.g. ObjC features don't overlap with C features, which means that ObjC is automatically compatible with the latest C standards).

In the end it's not a big deal of course, C and C++ are now entirely different languages and longterm that's for the better. Even the C++ peeps seem to have come to that realization and no longer recommend to "compile C in C++ mode" (like Herb Sutter in 2012 when trying to justify why MSVC had no C99 support: https://herbsutter.com/2012/05/03/reader-qa-what-about-vc-an...):

    "We recommend that C developers use the C++ compiler to compile C code (using /TP if the file is named something.c). This is the best choice for using Visual C++ to compile C code."

Did you use an LLM to write this comment? (I don't mean this as an accusation, I'm uncertain. I'm just trying to calibrate myself.)

Edit: I should've had more conviction in my instincts, this is slop.