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Tell HN: C Experts Panel – Ask us anything about C

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Re: Tell HN: C Experts Panel – Ask us anything about C

#541

Post by rseacord »

rurban wrote: post #533

1. When will we get proper strings in the stdlib? 2. When we will get the Secure Annex K extensions? 3. When we will get mandatory warnings when the compiler decides to throw away statements it thinks it doesn't need? Like memset or assignments. Compilers are getting worse and worse, and certainly not better. ad 1) Strings are Unicode nowadays, not ASCII. Nobody uses wchar but Microsoft. Everybody else is using utf8,…

For (2) I guess it depends. Annex K is obviously already a part of the standard so it depends on the implementation. There is a push to eliminate Annex K altogether from the C Standard. If this push fails, it may be the case that more libraries will add support for this optional feature of the language. In the meanwhile, there is the Open Watcom compiler implementation [1], the Safe C Library [2], and Slibc [3].

[1] Watcom C Library Reference Version 1.8. Open Watcom. 2008. ftp://ftp.openwatcom.org/manuals/current/clib.pdf

[2] Safe C Library — A full implementation of Annex K https://github.com/rurban/safeclib/

[3] slibc https://code.google.com/archive/p/slibc/

Re: Tell HN: C Experts Panel – Ask us anything about C

#542

Post by iainmerrick »

joosters wrote: post #486
iainmerrick wrote: post #443

Earlier quoted context omitted.

the compiler is allowed to assume the loop terminates precisely because signed overflow is undefined. Just to be sure I understand the fine details of this -- what would the impact be if the compiler assumed (correctly) that the loop might not terminate? What optimization would that prevent?

If the compiler knows that the loop will terminate in 'x' iterations, it can do things like hoist some arithmetic out of the loop. The simplest example would be if the code inside the loop contained a line like 'counter++'. Instead of executing 'x' ADD instructions, the binary can just do one 'counter += x' add at the end.

What I’m driving at is, if the loop really doesn’t terminate, it would still be safe to do that optimization because the incorrectly-optimized code would never be executed.

I guess that doesn’t necessarily help in the “+=2” case, where you probably want the optimizer to do a “result += x/2”.

In general, I’d greatly prefer to work with a compiler that detected the potential infinite loop and flagged it as an error.

Re: Tell HN: C Experts Panel – Ask us anything about C

#544

Post by radford-neal »

emilfihlman wrote: post #344
hsivonen wrote: post #317

Earlier quoted context omitted.

In practice not. In theory, it’s implementation-defined whether yhere are differences.

At least from what I've heard that's because stdint values are optional. 6.2.5p17 The three types char, signed char, and unsigned char are collectively called the character types. The implementation shall define char to have the same range, representation, and behavior as either signed char or unsigned char. 48) and 5.2.4.2.1 says that width of char, signed char and unsigned char are the same (8).

I don't think it's anything to do with uint8_t being optional. It's because a char might have more than 8 bits.

Re: Tell HN: C Experts Panel – Ask us anything about C

#545

Post by graycat »

aw1621107 wrote: post #445
graycat wrote: post #284

(1) Explain just how malloc() and free() work under the covers and the implications for multi-threading, memory leaks , virtual memory paging, etc. Maybe also cover some means, algorithms, and code for reporting on the state , status, etc. of the memory use by malloc() and free(). By the way, I know and have known well for longer than most C programmers have lived JUST what the heap data structure, as used in "heap s…

> Explain just how malloc() and free() work under the covers and the implications for multi-threading, memory leaks, virtual memory paging, etc. > > Maybe also cover some means, algorithms, and code for reporting on the state, status, etc. of the memory use by malloc() and free(). Strictly speaking, these are implementation details that the C standard leaves unspecified. If you want to know how the memory allocation…

Thanks.

> Did you have more specific questions in mind?

On stack overflow, my understanding was that could encounter that fatal condition from suddenly a too deep call stack, that is, too many calls without a return. So, if the "stack" is a, say, finite resource, then the programmer should know in the code how much of that resource is being used and act accordingly.

For a preprocessor for C++, I IIRC at one point the definition of C++ was in terms of a preprocessor -- I was just thinking of the definition, that is, get a more explicit definition of C++. I've always understood that always or nearly so C++ implementation was usual compilation. The issue is that at least at one time it seemed difficult to be precise about C++ semantics, that is, what the code would do and how it would do it. Maybe now C++ is beautifully documented.

Re: Tell HN: C Experts Panel – Ask us anything about C

#547

Post by DougGwyn »

clarry wrote: post #341

Open up WG14 mailing list for non-members? It's hard to appreciate what's going on at WG14 (or take part) when you can see the results only from afar, with none of the surrounding discussion. I recently read Jens Gustedt's blog on C2x where he casually recommended this as a way to get involved: "The best is to get involved in the standard’s process by adhering to your national standards body, come to the WG14 meeting…

In general, the committee accepts what we used to call "defect reports" (now something like "requests for improvement"), assigns them "WG14 series" sequence numbers, and upon requests for "floor time" schedules meeting discussions. Occasional votes are taken, which might trigger modifications to the draft standard. At some point, the committee decides that the updated draft standard is ready for public review, and the various national representatives deal with review comments. All this starts with proposal documents in "WG14 series" form.

Re: Tell HN: C Experts Panel – Ask us anything about C

#549

Post by smasher164 »

rseacord wrote: post #10

So what do people think about having a feature in the C language akin to the defer statement in GoLang? The GoLang defer statement defers the execution of a function until the surrounding function returns. The deferred call's arguments are evaluated immediately, but the function call is not executed until the surrounding function returns. It looks like an interesting mechanism for cleaning up resources.

I would love to see defer in the language. It helps keep cleanup code close to the resource that is acquired.

Would the proposed defer statement apply to loops as well? How would one implement such defers without dynamic allocation?

Re: Tell HN: C Experts Panel – Ask us anything about C

#550

Post by rseacord »

Many of your remaining questions have devolved into "When will I see my favorite feature xyz appear in the C Standard?" The answer in most cases is "that depends on how long it takes you to submit a proposal". Take a look at http://www.open-std.org/jtc1/sc22/wg14/www/wg14_document_log... for previous proposals and review the minutes to see which proposals have been adopted. In general, the committee is not going to adopt proposals for which there is insufficient existing practice or haven't been fully thought out. There are cases where people have come to a single meeting with a well-considered proposal that was adopted into the C Standard. I wrote about one such case here: https://www.linkedin.com/pulse/alignment-requirements-memory... Alternatively, you can approach someone on the committee and ask us to champion a proposal for you. It is likely that we'll agree or at least provide you with feedback on your proposal.
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