If you think C++ is not overly complicated, just what is a protected abstract virtual base pure virtual private destructor and when was the last time you needed one?
What about the zinger, “if you think English is not overly complex, just what is a loud old fast tall red car, and when was the last time you needed one?” No language I’m familiar with limits the number of adjectives you can use for a single noun. That doesn’t mean you generally should string several adjectives together; usually you’re fine just saying “car,” but sometimes you need the ability to be specific. English is a complicated language, but limiting how many adjectives can apply to a particular noun would make it much worse in my opinion.
As for the original question, a pure virtual function is a function that must be implemented in a derived class, while a private function is a function that can’t be accessed outside of the class, not even from derived classes. A destructor is a function used to clean up when an object goes out of scope; I don’t think anything about the destructor is important in this case, it just happens to be a convenient member function to use.
The combination would make it impossible to instantiate objects of the class (because of the pure virtual function) or objects of classes that inherit from it (because the pure virtual function can’t be accessed, let alone implemented, from a derived class). That rules out much of what you’d want to do with a class. You’re left with static data and functions, and nested types. Overall, the best I can tell, you would use that to make the class imitate a namespace. But for the last twenty years, you don’t have to imitate namespaces: C++ has them.
You might still find somebody trying to avoid using actual namespaces because of a vague fear of argument dependent lookup, but to be honest, I’ve never seen argument dependent lookup call the wrong function. Some programmers oppose it in principle, but in practice it doesn’t seem to cause much trouble.
I could be wrong but I think the above poster hasn't actually written tons of C, or else they would have picked a much more complicated example. If you throw a bunch of arrays, pointers, and function pointers in it quickly gets out of hand, like this:
int (* const(*foo)(int (*)(int, int))[5])(void);
Thankfully, you rarely run into something like that in the wild. And if you `typedef` the function pointers (Which is a pretty common now) it becomes tons easier to read.
I find this much easier to understand than something with different keywords and qualifiers. Function pointers follow some simple rules to read, but can you be sure of what `volatile` implies ?
Hmm, I suppose we just disagree then, which is fine. Things like `restrict` and `volatile` don't really bother me because:
1. The spots where people actually need to use them are very rare (`restrict` does have uses, but almost nobody uses it commonly. `volatile` has pretty much no correct uses outside of accessing registers in low-level code).
2. It's still just a pointer to a long long. I would need to look-up what __declspec((dllimport)) does, and I'd be highly suspicious of the use of `restrict` and `volatile` if it was not explained, but I still generally know what it is and how it can be used. Whereas with the example I gave, without staring for a long time or throwing it into a parser I can hardly tell what the type even is, let alone wrap my head around how it will be used.
Sorry, but what are you guys on about? You use "volatile" if you don't want the compiler to produce code that caches a variable. You use it all the time in embedded systems, or when writing multi-threaded code, etc. The usage of "volatile" is very clear, and should be well understood. "restrict" isn't used much because it's a c99 standard first of all, and second of all, it's like "inline"; it might make a difference, might not, and not a lot of people are in a situation where they have to shave off cycles.
Thanks for providing a very nice exhibit of the confusion around this. Volatile is 99% useless for multithreading code (unless on MSVC which has a peculiar interpretation of the standard). See https://stackoverflow.com/a/4558031/1495627
No amount of fences or mutexes is going to help you if threads are operating on their own version of a variable that got cached in a register, or optimised away. You need to understand volatile to write correct multi-threaded code.
That StackOverflow answer is bogus, along with all the other comments. It's just a rant that, albeit correct, is barely related to the question asked, and it's a clear example why you shouldn't treat StackOverflow as more than an unreliable help forum. The guy asked about whether you should make variables shared inside of a critical section volatile. The answer is "yes, to prevent threads from working on stale data".
Any properly written Mutex or similar implementation is going to act as a full memory barrier and compiler barrier, meaning variables will already not be cached across lock/unlock. And if you're not properly taking your locks before accessing your variables, `volatile` is not going to save you. The fact is, if you're using a lock to protect a variable, marking it `volatile` gains you nothing and just slows your code down.
> "yes, to prevent threads from working on stale data".
`volatile` absolutely does not guarantee a variable doesn't contain 'stale' data. That's the entire reason you need memory barriers in the first place. Even through the compiler will read a `volatile` variable from memory every time, that memory may still have a stale value in the CPU cache, which `volatile` will do nothing to prevent. Only proper use of memory barriers ensures everyone is working on the same thing, which `volatile` does not do.
Yes, it will! Just because you’re accessing shared variables doesn’t mean you need locks. This is what volatile is for!
You’re blindly hoping the compiler will do the right thing for you, anyway. You must have little-to-no experience writing multi-theaded code in production, let alone anything more advanced that doesn’t rely on locks.
Nobody’s arguing that volatile somehow bypasses the cache. When it comes to multithreading, that doesn’t matter though, because the whole process works with the cache, and the CPU keeps core caches synchronized. Memory barriers do nothing here.
Seriously, you’re arguing rubbish.
FWIW, it doesn't even do this, it's just a compiler-level annotation:
volatile int x = 0;
int foo() {
// read
int ret = x;
(void)x;
// write
x = 0;
x = 1;
return ret;
}
volatile's one of the simplest modifiers to understand if you care to actually learn the language. It has a clear, and well-defined purpouse, and i have no idea how you can spend so much time, and energy arguing that that's not the case.
None of it makes the language inherently any more complex, any more than representing machine instructions by long strings of binary makes _them_ any more complex.
With a boatload of associated semantics, quite a bunch bein in practice compiler-dependent (looking at you, MSVC volatile).
And a "protected abstract virtual base pure virtual private destructor" does not mean anything -- or at least any code that compiles.
Which is not part of C. Your argument that "C is complicated" doesn't work if you cite an egregious misuse of nonstandard extensions.