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Closed 10 years ago.
What does it mean "register a class", if we are talking about C++ and OOP, not about register, COM or some other libraries?
In the context of pure C++, without respect to any specific platoform or library, "register a class" has no meaning. This is not a language concept, nor is it any design pattern I am aware of.
It does however have at least two meanings the Windows world. For posterity and future readers:
You can register a Window class. A Window class contains some basic functionality and other parameters that effect how specific windows behave on-screen.
You can register a COM class so that specific instances of that COM class can be instantiated by clients.
"context was in articles about OOD, and it was said something like it is good practice to plan your classes in the way that for changing some aspect of program it will be enough to write new class, register it and you get new staff"
Now it seems to me you are talking about the publisher/subscriber pattern. It allows loose coupling between caller and callee.
You can find a C++ implementation everywhere, in the GoF book, or here:
http://rtmatheson.com/2010/03/working-on-the-subject-observer-pattern/
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Closed 9 years ago.
I am from JAVA so please please guide me if i am wrong.
In Java we mostly use a singleton class and create all the class objects thought the singleton class.
What about in c++?
I know we can use singleton but mostly while going through most of the stack overflow questions. Most of them says it's not good to use singleton in c++
Can you recommend some book or some project which will be easy to understand?
Whether you're writing in C++ or Java singletons have many, bad implications.
They make it very difficult to test as their static nature preculdes late binding to, say, sway a real database with a stub that's quicker and has fewer depencies.
They also provide a fig leaf for global variables, trying to make them masquerade as a good design decision. Take a look at the alternatives, it'll pay off in a better design. You may want to look into dependency injection for ways to design a more testable system without singletons.
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Closed 10 years ago.
Here's the problem: I'm developing a framework (CLCuda, not the most creative name out there) where the programmer instantiates one object, and depending on what the system supports (CUDA or AMD OpenCL), will use the corresponding methods, without having to change any line of code to that.
I have a abstract class named CLCuda (pure virtual methods, but could be just virtual), and the two classes that implement its methods are CLCudaCUDA and CLCudaOPENCL.
I wanted to have something like this: instantiate one object that will iniciatlizate CUDA or OpenCL, depending on what graphics card the user have, that can access the methods of the available platform (through the class CLCudaCUDA or CLCudaOPENCL).
I already coded the methods of CLCudaOpenCL and CLCudaCUDA (hard times doing that), so my problem is with OOP.
How could I structure my classes?
If anyone can help... thanks very much!
Your problem seems to suggest a "Factory" design pattern. Presumably you have a method to determine which is supported on the current host, so you should leverage that in the implementation of your factory.
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Closed 10 years ago.
I have a strategy pattern, and would like to run it in a main loop in a game for example. The problem is there will be a memory leak If I'm not deleting the instance, and I also would like to use that instance somewhere else. How can I deal with memory allocation/deallocation in a strategy pattern.
CompressionContext *ctx = new CompressionContext();
//we could assume context is already set by preferences
ctx->setCompressionStrategy(new ZipCompressionStrategy());
//get a list of files
ctx->createArchive(fileList);
Use an std::shared_ptr<CompressionContextBase> instead of a CompressionContextBase* (i.e. a raw pointer).
Edit: This is just a suggestion, based on the information you provided, there may be other smart pointer implementations with different semantics, such as e.g. unique_ptr, which might be more suited. As #akappa suggests, you may want to read up on the topic more, to make a better decision -- again, based on the information in the question, you probably want a shared_ptr but there might be additional considerations you omitted.
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Closed 11 years ago.
When reading the documentation of one or another boost library, I encountered some statements giving a hint that the virtual keyword is kind of evil. See http://www.boost.org/doc/libs/1_46_1/libs/msm/doc/HTML/ch03s05.html, for example:
It will not be said that MSM forces the virtual keyword down your throat!
According to http://www.parashift.com/c++-faq-lite/virtual-functions.html#faq-20.4, the virtual keyword is really not that bad, and my feeling about it is the same.
Why do some of the boost people regard virtual function calls as the worst thing ever? I have the impression that the boost guys are really the experts on C++, so there must be something about it.
there is case where static polymorphism is preferred to dynamic one. That's what Christophe states here. Nothing more.
Runtime polymorphism has an extra cost, namely the vtable. Once the vtable is added in a type, it can't be removed. One of the core strengths of C++ is that "you only pay for what you use". Therefore, to keep objects as lean as possible, several libraries avoid virtual functions when possible. Not because it is evil, but because you may not want it.
I think the inference is that MSM does not, through its inner workings or structure, force you to declare members of your own code as virtual, or to override theirs. There are libraries that require this, for instance libraries that dynamically create "proxies" of your classes such as mocks or lazy-loaders.
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Closed 12 years ago.
Please, could you explain, which technique is common for developing API for C/C++ programs?
One example is sockets. And what else?
Thanks...
Have a look at the APIs standardised by the Khronos Group. They have a well-established convention of defining library interfaces in a concise way.
No, they probably don't hold the Guiness record for "Most convenient API", but they indeed could have one for "Most consistent API stanard", "Best legacy API deprecation model" or something of those sorts.
One example of such API is the OpenGL's.
Don't develop your own system API. There's plenty of documentation on them already.