virtual | 易学教程

CRTP to avoid virtual member function overhead

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问题 In CRTP to avoid dynamic polymorphism, the following solution is proposed to avoid the overhead of virtual member functions and impose a specific interface: template <class Derived> struct base { void foo() { static_cast<Derived *>(this)->foo(); }; }; struct my_type : base<my_type> { void foo() {}; // required to compile. < Don't see why }; struct your_type : base<your_type> { void foo() {}; // required to compile. < Don't see why }; However it seems that the derived class does not require a

undefined reference to vtable - virtual member, classes generated by gsoap

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问题 gsoap with its tools wsdl2h and soapcpp2 provided me with a soapStub.h file containing the following: class SOAP_CMAC ns2__SOAPKunden { public: std::string *adresszusatz; // ... public: virtual int soap_type() const { return 7; } // ... ns2__SOAPKunden() : adresszusatz(NULL), x(NULL) { } // left out all member init. virtual ~ns2__SOAPKunden() { } }; I start with a small app using the class to populate objects with data from informix DB. But to compile successfully i have to leave away all the

What things (or in what cases) can make C++ slower than C ?

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问题 This is an interview question, the interview has been done. What things can make C++ slower than C ? The interviewer asked it very deep and always asked "anything else ? " whenever I said something. My ideas: C++ features not available in C may have some cost. For example, if we use assignment to initialize class's members inside a constructor not by the initialization list, the member's default constructor may be called once before the body of the constructor, and then that value wiped out

Why is 'virtual' optional for overridden methods in derived classes?

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问题 When a method is declared as virtual in a class, its overrides in derived classes are automatically considered virtual as well, and the C++ language makes this keyword virtual optional in this case: class Base { virtual void f(); }; class Derived : public Base { void f(); // 'virtual' is optional but implied. }; My question is: What is the rationale for making virtual optional? I know that it is not absolutely necessary for the compiler to be told that, but I would think that developers would

运行时类型识别（RTTI）

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dynamic_cast转换 dynamic_cast执行两步操作，先验证转换是否有效，有效则进行实际转换 class Base { public: virtual void fun1(void){printf("this is Base fun1().\n");} virtual void fun2(void){printf("this is Base fun2().\n");} virtual void fun3(void){printf("this is Base fun3().\n");} }; class Derive : public Base { public: virtual void fun1(void){printf("this is Derive fun1().\n");}; virtual void fun2(void){printf("this is Derive fun2().\n");}; virtual void fun3(void){printf("this is Derive fun3().\n");}; }; int _tmain(int argc, _TCHAR* argv[]) { // 将基类指针转换为派生类指针 Base *pBase = new Derive(); // 转换失败dynamic_cast返回0 if (Derive

4GB/4GB Kernel VM Split

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问题 Friends, I saw this article by Ingo Molnar, a famous Linux Kernel enthusiast where he talks about 4GB/4GB split. In this article he says that with the 4G/4G patch, the kernel can be compiled in 4G/4G mode, in which case there's a full, separate 4GB VM for the kernel, and there are separate full (and per-process) 4GB VMs for user-space. My problem starts here: My assumption was that in a monolithic kernel like as in Linux, the kernel and user part of process shares same PROCESS ADDRESS SPACE.

Polymorphism and casting

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问题 I want to understand polymorphism in c# so by trying out several constructs I came up with the following case: class Shape { public virtual void Draw() { Console.WriteLine("Shape.Draw()"); } } class Circle : Shape { public override void Draw() { Console.WriteLine("Circle.Draw()"); } } I understand that in order to send the Draw() message to several related objects, so they can act according to its own implementation I must change the instance to which (in this case) shape is 'pointing' to:

Python的历史

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【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> 　　Python的创始人为Guido van Rossum。1989年圣诞节期间，在阿姆斯特丹，Guido为了打发圣诞节的无趣，决心开发一个新的脚本解释程序，做为 ABC 语言的一种继承。之所以选中 Python（大蟒蛇的意思）作为程序的名字，是因为他是一个Monty Python的飞行马戏团的爱好者。　　ABC是由Guido参加设计的一种教学语言。就Guido本人看来，ABC 这种语言非常优美和强大，是专门为非专业程序员设计的。但是ABC语言并没有成功，究其原因，Guido 认为是非开放造成的。Guido 决心在 Python 中避免这一错误（的确如此，Python 与其它的语言如C、C++和Java结合的非常好）。同时，他还想实现在 ABC 中闪现过但未曾实现的东西。　　就这样，Python在Guido手中诞生了。实际上，第一个实现是在Mac机上。可以说，Python是从ABC发展起来，主要受到了Modula-3（另一种相当优美且强大的语言，为小型团体所设计的）的影响。并且结合了Unix shell和C的习惯。　　Python在编程语言中的定位　　很多大规模软件开发计划例如 Zope， Mnet 及 BitTorrent. Google都在广泛地使用它。　　通常认为

c++学习经典书籍

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先列举些c++学习经典书籍 C++： > 《C++ Primer》（fouth edition）：C++经典入门读物 > 《The C Programming Language》：C++之父著作，比较晦涩高深，不推荐初学者阅读 > 《Effictive C++》：C++进阶读物 > 《More Effective C++》：C++进阶读物 > 《Inside C++ Object Model》：C++内核对象的探讨 > 《Modern C++ Design》：前卫的C++编程方法，天马行空的编程思想 Windows： > 《Programming Windows》：win32 API编程的不二法门 > 《WINDOWS核心编程》：windows的内核编程操作，底层开发必学 > 《WINDOWS网络编程技术》：可视情况选择（是否对网络编程感兴趣） VC： > 《Programming Windows With MFC》：微软官方指定的MFC读物（类似教材的东东） > 《深入浅出MFC》：侯捷的探讨MFC本质的经典之作，不过对于应用者不推荐深入MFC，会用即可。再转录一段别人的阅读心得 1.在你学习C++的过程中,你首先需要扎实的实践一本C++基础教程,这个教程不在深而在全.使你能够全览之.最好结合基本数据结构来练习.不要整天Hello World~~Hello MM的. 2

Internal Workings of C# Virtual and Override

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问题 The topic of how C# virtual and override mechanism works internally has been discussed to death amongst the programmers... but after half an hour on google, I cannot find an answer to the following question (see below): Using a simple code: public class BaseClass { public virtual SayNo() { return "NO!!!"; } } public class SecondClass: BaseClass { public override SayNo() { return "No."; } } public class ThirdClass: SecondClass { public override SayNo() { return "No..."; } } class Program {