Earlier quoted context omitted.
What if there is no null?
If there isn't a NUL, then you're asking for a property relevantly distict from length of a datum relevantly distinct from a C-string. Use `strchr(s,0x00)` or `memchr(s,0x00,zs)`.
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Massacring C Pointers
241–250 of 300 posts
Re: Massacring C Pointers
#242Earlier quoted context omitted.
What if there is no null?
Then you probably shouldn't feed it to the str* functions at all. Use the mem* functions instead.
That's the same as saying you should never use the str* functions. Nothing in C guarantees a string must have a null byte. As you're well aware, C-strings aren't a separate type that's distinct from char arrays.
Sure you can say that good programmers will always ensure a C-string is a C-string but there's decades of programming history that shows that's not true in practice.
Re: Massacring C Pointers
#243When I started my CS degree the school was transitioning from teaching C++ to teaching Java, and the state of instruction in C++ was almost as bad as these examples. I had a professor who wanted us to use "new Foo()" everywhere in our code (even local / static variables) because it, "gets the students ready for Java." No matching delete, of course, or mention of RAII. We were supposed to "pretend" we had a garbage co…
> I think he took it with more grace than I deserved. You mean he gathered all of his students, colleagues, and superiors; officially admitted to faking knowledge where there was none, and solemnly apologized, promising never again to teach things he doesn't understand? I somehow doubt it, even though teaching nonsense to eager youth from the position of authority is an offense damn close to sexual molestation of min…
> ... an offense damn close to sexual molestation of minors ...
Wow, that's remarkably offensive.
Re: Massacring C Pointers
#244Yesterday I encountered a similar program on a HN comment chain as shown in this link. I am genuinely confused as to why this program is bad. I am a student and I do not know the best practices regarding pointers, but it is how I would write a program to combine two strings. Can someone please elaborate why it is bad? Are their any good resources to fill gaps in my knowledge? Thanks in advance. Edit: Thank you guys f…
I haven't touched C in years, but here's my descending "wtf" list: 1. Returns pointer to stack-allocated data, which immediately becomes invalid. Instead, it should be using some sort of allocation (e.g. 'malloc'), or taking in a destination pointer. 2. 'r' is arbitrarily set with length 100. Smaller strings don't need all that space, and larger strings definitely will overrun. 3. The function signature is really awk…
I've mentioned elsewhere that strncpy is not a "safer" strcpy.
Even if it were, there's safety and there's safety. A function (like strncat, for example) that quietly truncates your data if it's too long isn't necessarily better than one that quietly ignores array overruns. Consider what happens if "rm -rf $HOME/tmpdir" is quietly truncated to "rm -rf $HOME/"
Re: Massacring C Pointers
#245When I started my CS degree the school was transitioning from teaching C++ to teaching Java, and the state of instruction in C++ was almost as bad as these examples. I had a professor who wanted us to use "new Foo()" everywhere in our code (even local / static variables) because it, "gets the students ready for Java." No matching delete, of course, or mention of RAII. We were supposed to "pretend" we had a garbage co…
Some of my professors also have ridiculous code standards or exam standards. One of them teaches "algorithms and data structures", but he's not allowing us to even use a break or continue in our loops because he thinks it's "bad practice". We end up with a nested hellhole. Another example from the same professor (correct me if I'm wrong on this as I'm not a C++ expert), but he's constantly inheriting from unique or s…
>Another example from the same professor (correct me if I'm wrong on this as I'm not a C++ expert), but he's constantly inheriting from unique or shared pointers in his classes. Like why though?
You are not wrong. This completely breaks my brain. I really would love to hear the professor's explanation for this.
Re: Massacring C Pointers
#246When I started my CS degree the school was transitioning from teaching C++ to teaching Java, and the state of instruction in C++ was almost as bad as these examples. I had a professor who wanted us to use "new Foo()" everywhere in our code (even local / static variables) because it, "gets the students ready for Java." No matching delete, of course, or mention of RAII. We were supposed to "pretend" we had a garbage co…
> I think he took it with more grace than I deserved. You mean he gathered all of his students, colleagues, and superiors; officially admitted to faking knowledge where there was none, and solemnly apologized, promising never again to teach things he doesn't understand? I somehow doubt it, even though teaching nonsense to eager youth from the position of authority is an offense damn close to sexual molestation of min…
As others have mentioned, your choice of comparisons here is, at a minimum, badly-chosen. Not to mention, completely inaccurate.
Re: Massacring C Pointers
#247Earlier quoted context omitted.
And that's why just going to the cheapest university is a bad idea.
My mid tier university has a fundamental problem where the lecturers aren't even hired to teach, they're hired for research. And since the university can't get enough American grad students to stay and be research slaves they bring in grad students from the third world. Then these grad students are required by law to teach a certain number of credit hours to conduct research and there you go. The result is every gene…
I think the problem is a misunderstanding of the purpose of the "mid tier university". The university is a research institution and not a vocational training institution. Students who wish to learn a trade (plumbing, computer programming, etc) can attend one of many fine (and possibly less expensive) public and private vocational training institutions that have relationships with local businesses that hire graduates.
Students who wish to explore topics and solve problems at the limits of current human knowledge generally enroll at the University. At these institutions, undergraduates have an opportunity to work in research laboratories and graduate students, postdocs and faculty have the responsibility to obtain grant funding to keep their labs operating. As a courtesy, occasional classes are taught (to get students up to speed on basic theory) but there is an expectation that students are self-driven and can figure things out on their own (hence its ok if the TA is not a native English speaker, etc).
TLDR: If you want to learn a trade, go to vocational school. If you want an education, go to University.
Re: Massacring C Pointers
#248This doesn't surprise me really. When I was at university the programming textbooks we had were vile nasty and plainly incorrect. And those of us who dared challenge it by writing correct, robust code were penalised as the staff teaching it didn't understand the domain of what they were teaching properly and didn't have any real experience and assumed we were doing it wrong. We learned quickly to approach education w…
Part of getting through an education program is learning the differences between the right answer and the expected answer. If the book says it is so, then it is so, even if you know it isn’t. Remember both “facts”. Keep one for the test and the other for reality.
Re: Massacring C Pointers
#249Earlier quoted context omitted.
I can use a sledgehammer to break my leg, but that doesn't mean the hammer is broken by design. I just have to be careful where I swing the hammer and what I hit with it.
If the sledgehammer defaults to "leg breaking mode" then it's broken. How often do you actually use strncpy actually intending it not to return a non-NUL terminated string on truncation? I hate this mentality in a lot of C circles that boils down to "there's no bad language, just bad programmers, man up pussy". I like C, I use it a lot, it's one of the first languages I learned and it's been my main "professional" la…
I'm not arguing that it's a completely perfect language. But broken is an incredibly strong word for something that works when used as described in the documentation.
I think the API designer was trying to be parsimonious and not assume too much about what you want to do with the data in your destination buffer. The requirement was to provide buffer overrun protection when the source string is too large, and this function provides that. Beyond that, the requirement that the character array be null-terminated is your decision.
In fact, if you determine that it isn't null-terminated you can do other things besides null terminate it yourself. You might want to provide a helpful error message to consumers of your API rather than truncating their input data silently. Or you may try reallocating your buffer until the string fits. There's actual error handling that you can do with this function. In contrast, automatically null terminating the string makes that more difficult.
The other issues that you have with C seem like preferences. There's nothing wrong with not breaking by default in a switch statement as long as you know that that's what happens.
Re: Massacring C Pointers
#250The fixed-location variable allocation strategy the author mentions is called overlaying or compile-time stack[0]. It's still very much alive today, thanks to architectures like 8051 that are not really stack-friendly (even though they do have a stack). > The Keil C51 C Compiler works with the LX51 Linker to store function arguments and local variables in fixed memory locations using well-defined names [0] http://www…
Is there anything I can read to learn more about overlaying in C? I was reading, to my limited abilities' limits, 2.11 BSD source and there was a lot of references to overlaying.
On a modern POSIX environment, you can hack together an approximation of an overlay by loading some code to an area of memory, mprotect( ptr, len, PROT_EXEC) the segment, ((int(*)())ptr)() to call the function and if you did everything right, you don't segfault too hard. Later, you can overwrite that area of memory with other code and repeat.
This is similar to what actually goes on under the hood of the dynamic loader. http://tldp.org/HOWTO/Program-Library-HOWTO/dl-libraries.htm...