virtual

The difference between virtual, override, new and sealed override

由 早过忘川 提交于 2019-11-26 11:49:47
问题 I\'m pretty confused between some concepts of OOP: virtual , override , new and sealed override . Can anyone explain the differences? I am pretty clear that if the derived class method is to be used, one can use the override keyword so that the base class method will be overriden by derived class. But I\'m not sure about new , and sealed override . 回答1: The virtual keyword is used to modify a method, property, indexer or event declaration, and allow it to be overridden in a derived class. For

C++ static virtual members?

由 筅森魡賤 提交于 2019-11-26 11:44:45
Is it possible in C++ to have a member function that is both static and virtual ? Apparently, there isn't a straightforward way to do it ( static virtual member(); is a compile error), but is there at least a way to achieve the same effect? I.E: struct Object { struct TypeInformation; static virtual const TypeInformation &GetTypeInformation() const; }; struct SomeObject : public Object { static virtual const TypeInformation &GetTypeInformation() const; }; It makes sense to use GetTypeInformation() both on an instance ( object->GetTypeInformation() ) and on a class ( SomeObject:

virtual assignment operator C++

由 为君一笑 提交于 2019-11-26 11:40:34
Assignment Operator in C++ can be made virtual. Why is it required? Can we make other operators virtual too? Brian R. Bondy The assignment operator is not required to be made virtual. The discussion below is about operator= , but it also applies to any operator overloading that takes in the type in question, and any function that takes in the type in question. The below discussion shows that the virtual keyword does not know about a parameter's inheritance in regards to finding a matching function signature. In the final example it shows how to properly handle assignment when dealing with

How does virtual method invocation work in C++?

由 对着背影说爱祢 提交于 2019-11-26 11:35:55
问题 How does Virtual Method Invocation work in C++? 回答1: Through virtual tables. Read this article, http://en.wikipedia.org/wiki/Virtual_table. I could explain it here, but the wikipedia does a better job than I could. 回答2: The C++ standard doesn't specify how the virtual function mechanism should be implemented. That said, I think all current C++ compilers use virtual tables. The common way to do this for classes which contain at least one virtual function to have a hidden pointer to a so-called

How to implement virtual static properties?

由 时光毁灭记忆、已成空白 提交于 2019-11-26 11:34:27
问题 As far as I know C# doesn\'t support virtual static properties. How to implement such a behavior in C# ? I want to archive that all derived classes of a base class must override a static property. Getting a derived type, I want to access to a static property called Identifier Type t = typeof(DerivedClass); var identifier= (String) t.GetProperty(\"Identifier\", BindingFlags.Static).GetValue(null, null); 回答1: For people who think about the same thing and reach this post by googling, consider

C++ RTTI

由 梦想的初衷 提交于 2019-11-26 10:33:21
1.RTTI RTTI的英文全部意思为Run-Time Type Identification，意思为“运行时类型判断”。RTTI的原理为对某一范型或者接口类型，在运行时再判断该类型或者接口的类型，然后运行对应类型的功能函数。 RTTI的类型的运用，在各种语言中广泛运用；对于JAVA来说，RTTI甚至被号称为JAVA的多态机制的基础。 2.C++中的RTTI 在C++中，RTTI的提出是在1993年，由Stroustrup B.提出（Stroustrup B., “Run-Time Type Identification for C++”, Usenix C++ C onference, Portland, 1993. ）。但RTTI的由于其他类型判断会造成低效率，造成部分编译器对RTTI支持性不好。VC++原来一直是不支持RTTI的。在华为的编码规范中，强制要求不用RTTI的写法。这造成了即使是资深C_++程序员，也可能不了解RTTI机制。 3.C++中都RTTI实现 在C++中，RTTI机制是通过虚函数表来实现的。在C++中，虚函数表和虚指针同时也是多态机制的基础。从这个意义上来说，RTTI一开始就和多态和虚函数紧密相关。在C++的RTTI中，是一定要有virtual关键字和虚函数的。 与仅仅的所谓多态属性不同的是，RTTI实现，需要三个元素： 1)dynamic_cast

Virtual Box下进入MacOS虚拟机Recovery模式并修改VirtualBox中MacOS虚拟机的分辨率

由 笑着哭i 提交于 2019-11-26 10:22:16
前言 为了避免root用户随意更改Mac硬盘里面的文件，从El Capitan 10.11开始Mac添加了Mac SIP系统完整性保护。但是因为启用了这个功能，那么在虚拟机里面安装的Mac想要修改分辨率将无法实现，所以首先要关闭这个功能。而Mac系统只能在安全模式下才能关闭这个系统，因此，我们首先要进入Mac的Recovery模式。 Virtual Box 下进入Recovery 模式 开启虚拟机的Mac系统，USB键盘按 Windows+R 进虚拟机的BIOS系统，选择 Boot Maintenance Manager 。 点击 Boot From File 选项。 点进去第一个EFI是默认的启动方式，而另外两个启动模式由于都是乱码所以要一个个试试，找到那个点进去有 <com.apple.recovery.boot> 这个启动项的那个，不是的按 Esc 就可以退出了，我的是第三个选项点进去有recovery模式。 选择**<com.apple.recovery.boot> 选项 选择 boot.efi**就可以在Virtual Box中进入MacOS虚拟机的Recovery模式。 关闭IPS系统保护 等到屏幕出现苹果过后，画面会进入语言选择界面，选择 以简体中文作为主要语言 就好。 选择实用 工具 → 终端 ，打开终端。 在终端输入命令： csrutil disable

Writing a Virtual Printer in .NET [closed]

由 巧了我就是萌 提交于 2019-11-26 10:18:15
问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 9 months ago . I\'m looking to create a virtual printer that passes data to my .NET application. I want to then create an installer that installs both the printer and the .NET application. It would we really nice to be able to write it all in C#, but I have a feeling that this will require a printer driver to be written is

C++ inherit from multiple base classes with the same virtual function name

由 允我心安 提交于 2019-11-26 10:01:38
问题 I tried this code: class A { virtual void foo() = 0; }; class B { virtual void foo() = 0; }; class C : public A, public B { //virtual void A::foo(){} //virtual void B::foo(){} virtual void A::foo(); virtual void B::foo(); }; void C::A::foo(){} void C::B::foo(){} int main() { C c; return 0; } It is OK when using the commented part, but when I try to write the definitions outside the class declaration, the compiler reports errors. I am using the MSVC11 compiler, does anyone know how to write

Is it OK to call abstract method from constructor in Java? [duplicate]

由 ℡╲_俬逩灬. 提交于 2019-11-26 09:11:00
问题 This question already has an answer here: What's wrong with overridable method calls in constructors? 7 answers Let\'s suppose I have an abstract Base class that implements Runnable interface. public abstract class Base implements Runnable { protected int param; public Base(final int param) { System.out.println(\"Base constructor\"); this.param = param; // I\'m using this param here new Thread(this).start(); System.out.println(\"Derivative thread created with param \" + param); } @Override
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