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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

#231

Post by msebor »

rmind wrote: post #184

A lot C programmers prefer to keep structures within the C source file ("module"), as a poor man's encapsulation. For example: component.h: struct obj; typedef struct obj obj_t; obj_t *obj_create(void); // .. the rest of the API component.c: struct obj { int status; // .. whatever else }; obj_t * obj_create(void) { return calloc(1, sizeof(obj_t)); } However, as the component grows in complexity, it often becomes nece…

The ELF visibility attributes solve the part of the problem at the binary level (by hiding private library APIs from the application). The rest should be doable by structuring the project sources and headers in a suitable way.

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

#232

Post by Tronic2 »

pcr910303 wrote: post #148

As there are a lot of C-masters lurking in this thread: How can one process unicode (UTF-8) properly in C? As a CJK person, I wish there was a robust solution. Are there any standardized ways or proposals? (Using wchar doesn't count.)

Ignore all character support in the standard library and handle UTF-8 as opaque binary buffers. If you need complex string algorithms, decode into UCS-4 (UTF-32). You'll find short encoding and decoding functions on StackOverflow. For case-insensitive comparisons and sorting, use an external library that knows the latest Unicode standard.

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

#235

Post by artursapek »

pascal_cuoq wrote: post #105
Lucasoato wrote: post #77

Is there any new programming language that you particularly love? Do you like the way programming is evolving?

As a member of the development team for a C static analyzer, I use OCaml, which is also my favorite programming language, but that is because I'm from the generation in which it was the new thing (I learnt it when it had the same level of maturity as Rust, at a time when Rust didn't exist). It helps that it's perfect for writing compilers and static analyzers. There are a lot of problems that seem a good match for Ru…

Why won't you ever find time? It should only take a good 20 hours of reading and playing with code before you start to grok it.

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

#236

Post by rwmj »

eqvinox wrote: post #193
rwmj wrote: post #171

Earlier quoted context omitted.

I believe the last proposal was in 2008 (ignore the try..finally stuff here): http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1298.pdf So I guess it needs someone to take that and update it, also to pull up a full list of current Linux software which is using this feature (which as I say these days is a surprising amount).

Here's our usage: https://github.com/FRRouting/frr/blob/master/lib/privs.h#L14... #define frr_with_privs(privs) \ for (struct zebra_privs_t *_once = NULL, \ *_privs __attribute__( \ (unused, cleanup(_zprivs_lower))) = \ _zprivs_raise(privs, __func__); \ _once == NULL; _once = (void *)1) This gives us a block construct that guarantees elevated privileges are dropped when the block is done: frr_with_privs(privs) { ...…

We have a nice macro for acquiring locks that only applies to the scope:

https://github.com/libguestfs/nbdkit/blob/e58d28d65bfea3af36...

You end up with code like this:

https://github.com/libguestfs/nbdkit/blob/e58d28d65bfea3af36...

It's so useful to be able to be sure the lock is released on all return paths. Also because it's scope-level you can scope your locks tightly to where they are needed.

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

#237

Post by pascal_cuoq »

rmind wrote: post #184

A lot C programmers prefer to keep structures within the C source file ("module"), as a poor man's encapsulation. For example: component.h: struct obj; typedef struct obj obj_t; obj_t *obj_create(void); // .. the rest of the API component.c: struct obj { int status; // .. whatever else }; obj_t * obj_create(void) { return calloc(1, sizeof(obj_t)); } However, as the component grows in complexity, it often becomes nece…

I am sorry I do not have an answer to your question. It's a very valid one and I would be interested in any pointer to an answer.

What I can say while we are on the subject, is that I have seen C code (most often C code that started its life in the 1990s, to be fair) that instead of showing an abstract struct in the public interface, showed a different struct definition.

Please don't do this. Yes, when compiling nowadays, eventually every compilation unit ends up as object files passed to a linker that doesn't know about types, but this is undefined behavior. It makes it difficult to find undefined behavior in the rest of the code because there is a big undefined behavior right in the middle of it.

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

#238

Post by lemaudit »

Hi,

Do you think Annex K of C11 will be widely adopted by programmers or unused? Why aren't people adopting it?

Do you see the use of any analysis tools that are particularly effective for finding memory safety issues?

C++ added in smart pointers to its specification. Are there any plans to do something similar in future C specifications?

Thanks!

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

#239

Post by Someone1234 »

dooglius wrote: post #225
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.

- In your example there's no guarantee that the length will be accurate, or that the data hasn't been modified independently elsewhere in the program.

- In other words you've created a fantastic shoe-gun. One update line missed (either length or data, or data re-used outside the struct) and your "simple" struct is a huge headache, including potential security vulnerabilities.

- Re-implementing a common error prone thing is exactly what language improvements should target.

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

#240

Post by jayp1418 »

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.

Have you given ada language a thought ? Also there are lot of competition your students can take part in https://www.makewithada.org/
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