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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

#221

Post by wcarey »

imglorp wrote: post #180
wcarey wrote: post #126

I'm teaching C to high schoolers as their first language, which is quite the adventure. Do you have any good advice or resources on how to introduce the way C treats the function stack and heap allocated memory? Most of my students struggle (naturally) with making sense of function scoped identifiers and pass-by-value semantics.

Curious what were the requirements to select C as a first high school language over many other choices? I imagine there's a balance of practicality (after the class), and then the usual questions about tooling, sharp edges, and ease of learning.

It's a three year rotation: Python, C (Unix), C (Arduino). My goal with the class is to teach ideas that will stand the test of time. C (and Unix) certainly fit that bill.

Happily, the tooling is the easiest part. Every student has a rasberry-pi running debian, no mouse, no window server, and no extraneous software. You can spool kids up on a nano-based C toolchain in one class period with remarkably few sharp edges. There's even some fun accidental learning the first time they nano their executable file.

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

#222

Post by msebor »

eqvinox wrote: post #90

What's the best way to deal with "transitive const-ness", i.e. utility functions that operate on pointers and where the return type should technically get const from the argument? (strchr is the most obvious, but in general most search/lookup type functions are like this...) Add to clarify: the current prototype for strchr is char *strchr(const char *s, int c); Which just drops the "const", so you might end up writin…

The committee has reviewed a proposal (document N2360) to for const-correct string functions.

But making function signatures const-correct solves only a small part of the problem. A new API can only be used in new code, and casts can remove the constness from pointers leaving open the possibility that poorly written code will inadvertently change the const object. An attempt to change a global variable declared const will in all likelihood crash, but changing a local const can cause much more subtle bugs.

In my view, a more complete solution must include improving the detection of these types bugs in compilers and other static and even dynamic analyzers even without requiring code changes. It's not any more difficult to do that detecting out of bounds accesses. (In full generality it cannot be done just by relying on const; some other annotation is necessary to specify that a function that takes a const pointer doesn't cast the constness away and modify the object regardless.)

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

#223

Post by 3JPLW »

rseacord wrote: post #119
nicoburns wrote: post #81

Are there any plans to "clean up C"? A lot of effort has been put into alternative languages, which are great, but there is still a lot of momentum with C, and it seems that a lot of improvements that could be done in a backwards compatible way and without introducing much in the way of complexity. For example: - Locking down some categories of "undefined behaviour" to be "implementation defined" instead. - Proper ar…

I think we are always looking at ways to "clean up C" but that this has to be done very carefully not to break existing code. For example, the committee recently voted to remove support for function definitions with identifier lists from C2x http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2432.pdf At least one vendor was not very happy with this decision. Undefined behaviors tend to be undefined for a reason and sho…

Does it concern you how aggressively compiler teams are exploiting UB?

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

#224

Post by rseacord »

sgawlik wrote: post #15

When you're looking at an unfamiliar C code base for the first time, how do you approach it? Which files do you look for? Which tools to you open up immediately?

This depends a bunch on what your goals are. There are no specially named files, so looking for a particular filename is not particularly useful. It is sometimes informative to find the file containing the main, but not always.

My job at NCC Group involves a lot of code reviews, so frequently the files that are of interest to me are the ones that contain the most defects. I typically identify these by compiling with compiler warnings turned up and warning suppression turned down. I'll frequently also make use of static and dynamic analysis, including the GCC and Clang sanitizers.

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

#225

Post by dooglius »

nicoburns wrote: post #81

Are there any plans to "clean up C"? A lot of effort has been put into alternative languages, which are great, but there is still a lot of momentum with C, and it seems that a lot of improvements that could be done in a backwards compatible way and without introducing much in the way of complexity. For example: - Locking down some categories of "undefined behaviour" to be "implementation defined" instead. - Proper ar…

You can very easily make a struct consisting of a pointer and length, is adding such a thing to the standard really a big deal? Personally, I don't see a problem with passing two arguments.

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

#226

Post by wcarey »

DougGwyn wrote: post #198
wcarey wrote: post #126

I'm teaching C to high schoolers as their first language, which is quite the adventure. Do you have any good advice or resources on how to introduce the way C treats the function stack and heap allocated memory? Most of my students struggle (naturally) with making sense of function scoped identifiers and pass-by-value semantics.

Everybody seems to draw pictures of the raw memory (word-oriented) data.

I've been doing the same! It certainly helps for strings. Pointer block diagrams (like K&R use) seem to help too. Mostly what melts their brains is the idea that an identifier can be "in two places at once" - for example, you can have a variable x declared in some scope and a function one of whose arguments is named x, and those are two different things.

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

#228

Post by stephencanon »

asveikau wrote: post #204
tlb wrote: post #163

Earlier quoted context omitted.

Another approach would be a standard library of arithmetic routines that signal overflow. If people used them while parsing binary inputs that would prevent a lot of security bugs. The fact that this question exists and is full of wrong answers suggests a language solution is needed: https://stackoverflow.com/questions/1815367/catch-and-comput...

Microsoft in particular has a simple approach to this with things like DWordMult(). if (FAILED(DWordMult(a, b, &product))) { // handle error }

Clang and GCC's approach for these operations is even nicer FWIW (__builtin_[add/sub/mul]_overflow(a, b, &c)), which allow arbitrary heterogenous integer types for a, b, and c and do the right thing.

I know there's recently been some movement towards standardizing something in this direction, but I don't know what the status of that work is. Probably one of the folks doing the AUA can update.

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

#229

Post by oreally »

About time someone advocated for code in lower level styles of programming. Hope it goes well!

Anyway, here's some questions:

- What kind of programs would you say C is a good fit for?

- There is some catching up to do for C. Is there a roadmap for C improvement, or even a recommendation of C++ things that fit somewhat in the style/philosophy of C? For example, I'd recommend not using the C++ smart pointers stuff, while still using C++ threads and lambdas.

Also, you should include programmers from other fields in your committee. Game (engine) developers, HFT programmers are used to lower level styles of coding and align with your perspective.

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

#230

Post by billpollock »

nchelluri wrote: post #169

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