Git's list of banned C functions • Hacker News Board

Re: Git's list of banned C functions

#621

Post by InvOfSmallC » Sat, Mar 06, 2021, 9:39 AM UTC

orwin wrote: post #184

InvOfSmallC wrote: post #103

Earlier quoted context omitted.

I teach at university as external lecturer. Teaching strings in C is the hardest thing I have to do every time. The university decided to explain C to first year student without previous experience. My feedback was to do a precourse in Python to let them relax a bit with programming as a concept and then teach C in a second course.

In my school, we had two days to understand the basics of text editors, git (add, commit, rebase, reset, push) and basic bash functions (ls, cd, cp, mv, diff and patch, find, grep...) + pipes, then a day to understand how while, if/else and function calls work, then a day to understand how pointer work, then a day to understand how malloc(), free() and string works (we had to remake strlen, strcpy, and protect them).…

I don't this looks like a beginners course though. My students have zero experience.

Re: Git's list of banned C functions

#622

Post by InvOfSmallC » Sat, Mar 06, 2021, 9:47 AM UTC

harpiaharpyja wrote: post #580

hguant wrote: post #312

Earlier quoted context omitted.

Python is great fun, and you can be really productive with it, but for people first coming into programming, a language with an explicit and strict type system is invaluable. I used to think that everyone should be taught python first, because it lets you focus on the meat of computer science - algorithms, data manipulation, actually _doing_ something - but after helping my girlfriend out with some comp sci 101-104 p…

I use Python a lot professionally these days, after having been a C#/Java developer for a while (and some experience with C and Free Pascal). I absolutely love the language. I always feel a little iffy when people talk about Python like it's a language ideally suited to beginners. Dynamic typing puts so much power in your hands to create expressive structures. But it requires discipline to use properly. It's a great…

My reasons for suggesting Python compared to Java for example is due to the fact that I teach to Electrotechnical engineers and there are plenty of libraries to experiment with Raspberry and stuff and it's a little bit higher level than C. Every language has its own difficulty to teach but the fact the companies have a banned.h it's basically saying "well C gives you functions for C, but don't use them". It makes it unecessary harder to explain something to people with no experience.

Re: Git's list of banned C functions

#623

Post by InvOfSmallC » Sat, Mar 06, 2021, 9:51 AM UTC

fho wrote: post #485

InvOfSmallC wrote: post #103

Earlier quoted context omitted.

I teach at university as external lecturer. Teaching strings in C is the hardest thing I have to do every time. The university decided to explain C to first year student without previous experience. My feedback was to do a precourse in Python to let them relax a bit with programming as a concept and then teach C in a second course.

Question: how do you teach for-loops? That is something I have a hard time convey as a teacher. My problem is that I have done this so long that I have no idea what there is not to understand about loops ... it's such a simple thing. But my (undergrad biology) students regularly have a hard time groking the concept no matter what explanation I use.

Well I took the time and made some simple animation of how that works. For that and pointers I use animation so they can visualize what's happening. (Wasn't my idea, I googled it "how to explain pointers")

Re: Git's list of banned C functions

#624

Post by InvOfSmallC » Sat, Mar 06, 2021, 9:54 AM UTC

paganel wrote: post #264

InvOfSmallC wrote: post #103

Earlier quoted context omitted.

I teach at university as external lecturer. Teaching strings in C is the hardest thing I have to do every time. The university decided to explain C to first year student without previous experience. My feedback was to do a precourse in Python to let them relax a bit with programming as a concept and then teach C in a second course.

You are a good teacher. 20 years ago I was in the exact situation of one of your students, i.e. I was put in front with the C language in the first semester of the first year. I barely, barely passed, failed with glory a similar course in the second semester which I only passed (with an A, to put it in US university terms) a couple of years later after I had managed to learn Python by myself in the meantime.

Thanks! I just think that you can get out of practical programming concepts (like loops, conditions) without the need to understand that a string is an array of chars and that chars are actually integers.

Because if remove the basics of programming with something like Python, you can fully concentrate on the second course on low hardware stuff, how to use memory etc..which is really important for my students, them being Electrotechnical engineers.

Re: Git's list of banned C functions

#625

Post by InvOfSmallC » Sat, Mar 06, 2021, 10:03 AM UTC

gravypod wrote: post #237

InvOfSmallC wrote: post #103

Earlier quoted context omitted.

I teach at university as external lecturer. Teaching strings in C is the hardest thing I have to do every time. The university decided to explain C to first year student without previous experience. My feedback was to do a precourse in Python to let them relax a bit with programming as a concept and then teach C in a second course.

Sorry to bug you since this is unrelated. I'm a huge fan of teaching others and I was wondering how you got to be an external lecturer at a college? I'd love to teach classes related to software engineering and data structures. Would you mind emailing me (in my profile) about this?

So this is what happened for me: I went for a walk in the forest with my wife and some of her friends. There was one friend that had an husband working at university.

We started talking and basically we discovered what he was teaching really related for what I do for work so he asked me to become a "mentor" meaning a professional that helps students with their thesys.

In the meantime I went to talk during his class about product management as an engineer where basically I said "I'm an engineer like you, go and talk to customers, it's part of the job", plus extreme programming stuff etc...

After that there was a position open and this professor recommended me because I told him it was one of my goals to be a teacher as well.

And then from there I met the head of dept. He was happy with me being versatile, I usually handle C, database design or java.

But the usual stuff is go to the university you like an look for open positions.

I need to get confirmed every semester and apply again. Usually this job is done by people with a main job and sometimes it happens you don't have time in a semester.

Re: Git's list of banned C functions

#626

Post by InvOfSmallC » Sat, Mar 06, 2021, 10:09 AM UTC

cblconfederate wrote: post #308

InvOfSmallC wrote: post #103

Earlier quoted context omitted.

I teach at university as external lecturer. Teaching strings in C is the hardest thing I have to do every time. The university decided to explain C to first year student without previous experience. My feedback was to do a precourse in Python to let them relax a bit with programming as a concept and then teach C in a second course.

thats probably because pointers are considered "hard" , too hard to exist in other languages. It's interesting that in the 80s, the standard library modeled C++ iterators with pointer semantics because they assumed everyone could do pointer arithmetic, but nowadays the concept is not mainstream at all.

But that's point right? I have two hours per week for a semester. So basically I tried to be really fast at the beginning with if else and loops, gave then an exercise that counted towards final score and then it was pointers and pointers related stuff.

Re: Git's list of banned C functions

#627

Post by slrz » Sat, Mar 06, 2021, 12:03 PM UTC

JoeAltmaier wrote: post #572

schlupa wrote: post #571

Earlier quoted context omitted.

strncpy() suffers from its naming. It never was a string function in reality. It is a function to write and clear a fixed size buffer. It was invented to write filenames in the 14 character buffer of a directory entry in early Unix. It should have been name mem-something and people would have never come to the idea to use it for general string routines.

If it respects null terminator, then it is a string function.

It basically expects a string as the source and a fixed-size, not necessarily zero-terminated, buffer as the destination.

Re: Git's list of banned C functions

#628

Post by arunc » Sat, Mar 06, 2021, 4:17 PM UTC

WalterBright wrote: post #533

dotancohen wrote: post #520

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Hello Walter! All things considered, you are probably the best person to ask for tips on string handling in C. Would you might sharing the things that you look for, from the obvious to the subtle? I would love to see some rejected push requests if possible. If I were writing C under your direction, what would you drill into me? Thank you, it is an honour to address you here.

1. whenever you see strncpy(), there's a bug in the code. Nobody remembers if the `n` includes the terminating 0 or nor. I implemented it, and I never remember. I always have to look it up. Don't trust your memory on it. Same goes for all the `n` string functions. 2. be aware of all the C string functions that do strlen. Only do strlen once. Then use memcmp, memcpy, memchr. 3. assign strlen result to a const variable…

With so many gotchas, it irks me when they still teach C for the undergraduates.

Re: Git's list of banned C functions

#629

Post by mettamage » Sat, Mar 06, 2021, 4:39 PM UTC

mrweasel wrote: post #478

adrianN wrote: post #458

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At what age are you a junior developer and at what age are you a junior psychiatrist in NL? A bachelor's developer could be as young as 21 I guess, but at least for most jobs in medicine you can't work independently until much later. Maybe it's different for psychiatry?

Junior developers aren't really a thing in many places. They're just developers.

In NL they are.

Re: Git's list of banned C functions

#630

Post by renox » Sat, Mar 06, 2021, 11:05 PM UTC

JoeAltmaier wrote: post #575

WalterBright wrote: post #533

Earlier quoted context omitted.

1. whenever you see strncpy(), there's a bug in the code. Nobody remembers if the `n` includes the terminating 0 or nor. I implemented it, and I never remember. I always have to look it up. Don't trust your memory on it. Same goes for all the `n` string functions. 2. be aware of all the C string functions that do strlen. Only do strlen once. Then use memcmp, memcpy, memchr. 3. assign strlen result to a const variable…

So many potential pitfalls to string functions. But memcpy and friends can have pitfalls too. I was working on a RISC processor and somebody started using various std lib functions like memcpy from a linux tool chain. I got a bug report - it crashed on certain alignments. Made sense - this processor could only copy words on word alignment etc. So I wrote a test program for memcpy. Copy 0-128 bytes from a source buffe…

>why the hell isn't there an instruction in every processor to efficiently copy from arbitrary source to arbitrary destination with maximum bus efficiency?

Uh, you're not an hardware designer and it shows.. What if there's a page fault during the copy, you handle it in the CPU? That said, have a look at RISC-V vectors instruction (not yet stable AFAIK) and ARM's SVE2: both should allow very efficient memcpy(among other things) much more easily than with current SIMD ISA.