Rule of Zero (C++)
rmartinho.github.com
rmartinho.github.com
Some additions:
- The least you allocate on the heap, the better. Move semantics really help in that aspect;
- Smart pointers are not magic. Although I really think using unique_ptr whenever possible is a good idea, shared_ptr comes with a performance cost (especially in multithreaded environments), can introduce vicious memory leaks and is often used as an excuse to not think your lifetime cycle through.
C++ suffered for a long time due to lack of quality libraries.
This now seems to be finally changing, at least until another language is a good enough replacement for it.
I am keeping an eye how D and Rust evolve, additionally Ada seems to be getting some users, at least here in Europe.
As for quality libraries, I'd almost say that we had too much of them. For every platform and every different C++ methodology/subset (from "C with Classes, ocassionally Structs" to "Post-Modern Template Abuse") had its own set of supporting libraries. Often good enough, but most of the time not the ideal source for your particular project, and very hard to integrate, if every code paragraph follows a different paradigm, depending on what library your calling.
Still don't see a good solution to that. Quite likely that your GUI library won't quite mesh with your collections, data parsing or network support.
I heard it at this year FOSDEM.
Since GNAT availability many universities seem to be making use of it. As for the industry I guess it still constrained to the usual types of systems where Human life is very important.
As for the libraries you're doomed to have that for all libraries that are not part of the standard library. Even the "comes with batteries" languages suffer from this when you need to integrate external libraries.
If Java and .NET didn't happen, maybe there would already be an InteliJ for C++. I am looking forward for the tooling progresses made possible by using the compiler as plugins, as clang shows.
Especially if the rest of the code base was the usual OO class forest.
I knew of Ada use in teaching, it seems to be quite popular for some advanced "software engineering" courses. Then again, I've seen a pretty great amount of Algol-family languages there, out of proportion to the actual practical use. Oberon was quite popular for a while, as it was a very small language to teach and the barriers to running your first programs were basically non-existant (as you can easily call your module function directly, compared to the rather perplexing "public static void main" of introductory Java courses).
Many library authors will choose to make a C interface instead, as that basically makes the library usable by almost any language, but C++ seems near the top when it comes to language-specific library support.
What are the C++ libraries for
- Networking
- XML
- Reflection
- ORM
- Database access
- UI
- Asynchronous programming
- Make use of std::string and STL, instead of providing their own types.
- Web Services
- ...
Don't forget that your list should provide libraries that work across multiple OS (UNIX and Windows are not enough) and multiple compilers (besides gcc, clang, msvc).
The libraries also need to be compatible with the possibility that the developers compile with exceptions, RTTI enabled/disabled.
Did you know that STL was actually developed in Ada and later on adopted to C++?
> Don't forget that your list should provide libraries that work across multiple OS (UNIX and Windows are not enough) and multiple compilers (besides gcc, clang, msvc).
EDIT: typo
Out of curiosity, what platforms do you need to use which are unsupported by Qt but work well with other languages...?
The consulting world is much more than just Linux/Windows/Mac.
Which languages/libraries work well in all environments?
Most of those environments have JVMs available. Although. a few of them, like i/OS, still only have Java 5 or 6 available.
Don't take me wrong I am not against C++ and do use it in some of my employer projects. Then again we need to fill our code with #ifdefs when the need to support multiple environments with different sets of compilers arises.
For example, even Boost with its exhaustible list of compilers and operating systems does not support:
- HP-UX
- i/OS
- QNX
- VxWorks
- Symbian (yes people still develop for them)
This is just one library, it gets worse if we need to take a few proprietary libraries into the equation.
Now, for doing native code programming, C++ is the best currently available language, and I wish that with C++11 and the upcoming revisions, it gets better.
I know it's beautiful language with a laundry list of features, but keeping things simple is still the best approach:
#define __no_copying(type) \
\
private: \
type(const type &); \
type & operator = (const type &); \
public:
class foo
{
public:
foo();
__no_copying(foo);
...
}
On one project I worked on as a contractor, and quite a large one at that, I removed every single one of them and rescoped the code base. It took a while but performance alone improved by about 400%
As others are pointing out they have advantages and disadvantages. It all depends on the situation. But they're certainly not free because they have a scope cost. Code size and simplifying compiler optimisation are important too. I think it's worth that pointing out.
Unfortunately it was slow, and as others have mentioned, sometimes difficult to debug and heap errors can propagate out of order, depending on other conditions.
I'm in no doubt about the value of the auto_ptr variants. However I'm often brought in to speed up projects that don't meet performance requirements, and it often entails rethinking structure, simplification, replacing generalised ctor dtor lists, and rediscovering where const references, independently of move semantics, lead to algorithmic questions that need reexamining. This leads back to encompassing scope, and from there it's often the right thing to institute a better model.
The benefit can be a lot less instructions and resultant speedups.
Perhaps I've had too many of these jobs, but hey, it's a living.
class foo : boost::noncopyable
{
public:
foo();
};foo(const foo &);
foo & operator = (const foo &);
to every class definition that needs it. Small amount of basic, simple C++ boilerplate > magic.
In this particular example it is very easy to screw it up. Your way involves many more lines of code and use of the preprocessor which makes searching through code very difficult. I can easily find all the noncopyable classes by searching for "noncopyable". I don't have to worry about someone coming along and screwing up the access modifier at a later date. It is much less likely that someone will misunderstand what the code is trying to do, even if they don't know much about C++ value semantics.
Edit: I guess my criticism regarding searching isn't valid here, but I have come to try and avoid the preprocessor as much as possible. I've just been bitten by it too many times.
class Noncopyable
{
private:
Noncopyable(const Noncopyable&);
Noncopyable& operator(const Noncopyable&);
};
No, it's not. This just a made-up argument.
> ... many more lines of code
6 in #define, one of which is blank. Your option however creates an external dependency on the library that somehow needs to be built even though it is supposed to be just a collection of headers.
> ... and use of the preprocessor which makes searching through code very difficult
Ok, considering your Edit, let's skip this one.
> I can easily find all the noncopyable classes by searching for "noncopyable".
Similarly, you can find all noncopyable classes by searching for "__no_copying". Besides, why on Earth you would ever need to do that in real life?
> I don't have to worry about someone coming along and screwing up the access modifier at a later date.
Ah, right. Here we start to really diverge. You are writing code that needs to be protected against incompetent colleagues, and I typically don't.
> It is much less likely that someone will misunderstand what the code is trying to do
No, of course it is not. This is too a made-up argument.
PS. I hate Boost with passion, because it drags C++ in the exact opposite direction from how I am, personally, using it, which is C with classes, uncomplicated inheritance and basic templating. This is beautiful and functional subset of C++ that retains the clarity of C and adds flexibility and convenience that latter is missing. Boost has its place, clearly, but I don't understand programmers who willingly use it, just as I don't understand those who like Bjork.
I guess you and I have had vastly different experiences. boost has improved my code immeasurably. I cannot stand the "C with classes" approach. All the code I've come across the uses that approach is always broken in subtle ways the could be avoided by using the simple utilities in boost. I think in the end it is probably just personal preference.
I'll agree with you about Bjork. But I am a serious musician and the best musician I have every been in the presence of loved Bjork.
I think many bugs could have been avoided by not typedef'ing our pointers, because when you have to type `std::shared_ptr<myclass>`, then you know what kind of pointer it is. On the other hand, if you have to, at least call the typedef `myclassSharedPtr` instead of `myclassPtr`. But for (2), I don't see a work-around. How can you write good code when your critical dependencies don't play nice?
I don't understand what you mean by this. If you have a `smart_ptr<T> p;` nothing prevents you from passing `*p` or `p.get()` to some legacy interface. You only have trouble if that legacy interface wants to claim ownership of the object.
That's exactly what I mean. This happens. My point is just that even the best intentions are easily subverted in a real-world scenario where you didn't write the whole codebase yourself from scratch.
On (2), I think the solution is intrusiveness. intrusive data structures and intrusive_ptr should be used more in C++.
The dislike for intrusiveness is rooted on equating classes with responsibilities. A single responsibility is often spread over several classes, because the classes form a useful cluster. A clear case is items of a collection. If an object already knows it's an item in a collection, there's really no harm in using intrusive lists.
Actually, I find that having fixed ownership makes much more sense than reference counting for the majority of cases. Example: we have a FileSystem, and a bunch of File's belonging to this FileSystem. Whenever a part of a program needs a file, it just initializes its own File object, and when it doesn't need it anymore, it releases it somehow (e.g. file.deinit() or destructor if RAII is used). Even if two users both need the same file, each gets its own File. The FileSystem internal implementation can take care of any resources sharing, invisible to the users.
As far as the memory management of FileSystem is concerned: again, in most cases, you don't need shared_ptr<FileSystem>. Just make sure the FileSystem stays alive as long as there's the possibility that anyone is using it. Like initialize it at the beginning of the program, and deinitialize it during shutdown at the right point.
Instead it allows the compiler and language to automatically do the right thing to enable RAII by using appropriate library-provided building blocks. E.g. his std::unique_ptr + custom deleter type enables the compiler to automatically make a RAII-compliant class for the author, so it's still RAII, just automatically implemented (except for the ctor, in this case).
You can read about the reasoning behind the new syntax here:
http://www.emarcus.org/papers/n1449.pdf
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n148...
template <typename T>
using MyVector = std::vector<T, MyAlloc>;
// strictly equivalent to typedef int MyInt;
using MyInt = int;This is one of the things that makes C++ mega-complicated. The same keywords have different meanings based on context, when really a new keyword should just have been used. For example "virtual" functions vs "virtual" inheritance.
It's for this reason, too, that Java 7 overloaded `try` to implement some sort of poor-man's-RAII-support, instead of adding a new keyword (such as C#'s `using`, which does the same, and was by the way also overloaded for the same reason)
That seems like typical Microsoft object-orientation. It's not really much of encapsulation. Reminds me of MFC :-/
However not everything went as they expected and people were also demanding something more light over Win16 and MFC was born.
http://computer-programming-forum.com/82-mfc/d13ea80282846f9...
Examples of things that require explicit clean up: -> Files -> Sockets -> Transactions
The C++ resource model can be applied to all resources, not just memory.
Garbage collection only "solves" memory management for you - often that's the least important resource that your program is managing.
C++ destructors benefit is that you don't forget to call such constructs.
You can if all "destructors" take care of also closing the internal resources, thus initiating a cascade process of the object owned by them.
But you're right, this leaves the responsibility in the user's side.
> I would give an arm and a leg for RAII on the JVM.
At least they finally added the "using" concept.
In a few more versions maybe they get to add values.
I think you're right but wrong here : it may be the least important in a technical sense, but the sheer amount of developer productivity lost in manual memory management is very expensive (for both the mental resources of the programmer and the firm), and this makes automated memory management a key positive.
Honestly, my eyes glazed over to avoid traumatic memories of C++ and Windows DOM internals as I read the article. I have a LIFE since I moved to Java.
Sometimes exact control is what you need. It is no use trying to stop any discussion on the subject.