virtual

Is there any sense in marking a base class function as both virtual and final? [duplicate]

由 醉酒当歌 提交于 2019-12-01 01:03:25
问题 This question already has answers here : What's the point of a final virtual function? (10 answers) Closed 2 years ago . In various explanations of C++11's final keyword, I'm seeing examples like this. class base { public: virtual void f() final; }; class derived : public base { public: virtual void f(); // Illegal due to base::f() declared final. }; Is this actually a useful use of final ? Why would you declare a virtual function in a base class (implying that it will be usefully

Access specifiers and virtual functions

由 南笙酒味 提交于 2019-12-01 00:47:57
What are the rules for accessibility when virtual functions are declared under 3 different access specifiers specified by C++(public, private, protected) What is the significance of each? Any simple code examples to explain the concept will be highly useful. Access specifiers apply in the same way as they would to any other name during name lookup. The fact that the function is virtual does not matter at all. There is a common mistake which sometimes happens with respect to virtual functions. If name lookup determines a viable function to be a virtual function, the access specifier of the

How to find with javascript if element exists in DOM or it's virtual (has been just created by createElement)

由 谁说胖子不能爱 提交于 2019-12-01 00:47:55
问题 I'm looking for a way to find if element referenced in javascript has been inserted in the document. Lets illustrate a case with following code: var elem = document.createElement('div'); // Element has not been inserted in the document, i.e. not present document.getElementByTagName('body')[0].appendChild(elem); // Element can now be found in the DOM tree Jquery has :visible selector, but it won't give accurate result when I need to find that invisible element has been placed somewhere in the

about the cost of virtual function

由 偶尔善良 提交于 2019-11-30 23:54:56
问题 If I call a virtual function 1000 times in a loop, will I suffer from the vtable lookup overhead 1000 times or only once? 回答1: The Visual C++ compiler (at least through VS 2008) does not cache vtable lookups. Even more interestingly, it doesn't direct-dispatch calls to virtual methods where the static type of the object is sealed. However, the actual overhead of the virtual dispatch lookup is almost always negligible. The place where you sometimes do see a hit is in the fact that virtual

Overloading a virtual function in a child class

由 こ雲淡風輕ζ 提交于 2019-11-30 22:33:51
问题 I am just testing with virtual keyword and inheritance concepts in c++. I have written a small program: #include<stdio.h> #include<iostream> using namespace std; class cna_MO { public: virtual void print() { cout << "cna_MO" << endl; } }; class cna_bsc:public cna_MO { public: void print() { cna_MO::print(); } void print(int a) { cout << "cna_BSC" << endl; } }; class cna_Mo { cna_MO *_mo; public: cna_Mo() { _mo = new cna_bsc; } virtual void print(int a) { cout << "cna_Mo with arg" << endl; _mo

Multiple inheritance and pure virtual functions

由 自作多情 提交于 2019-11-30 22:05:13
问题 The following code: struct interface_base { virtual void foo() = 0; }; struct interface : public interface_base { virtual void bar() = 0; }; struct implementation_base : public interface_base { void foo(); }; struct implementation : public implementation_base, public interface { void bar(); }; int main() { implementation x; } fails to compile with the following errors: test.cpp: In function 'int main()': test.cpp:23:20: error: cannot declare variable 'x' to be of abstract type 'implementation

Convert character to the corresponding virtual-key code

由 二次信任 提交于 2019-11-30 21:24:53
Currently, I'm using the method VkKeyScan in the Win32 API to convert a character to its virtual-key code. But the problem that this seems to have is that, when i pass small alphabets, it works fine whereas when i pass in a capital alphabet, it doesn't return the appropriate key code and similarly with special characters like "(" or "}". How do i do this? Is there anyway for me to directly convert a string to its virtual equivalent without considering whether it contains capitalized or special characters? Thanks You should be clearer in what your requirements are, more specifically in what you

Why C++ virtual function defined in header may not be compiled and linked in vtable?

由 风流意气都作罢 提交于 2019-11-30 21:08:10
Situation is following. I have shared library, which contains class definition - QueueClass : IClassInterface { virtual void LOL() { do some magic} } My shared library initialize class member QueueClass *globalMember = new QueueClass(); My share library export C function which returns pointer to globalMember - void * getGlobalMember(void) { return globalMember;} My application uses globalMember like this ((IClassInterface*)getGlobalMember())->LOL(); Now the very uber stuff - if i do not reference LOL from shared library, then LOL is not linked in and calling it from application raises

RabbitMQ安装

由 ￡可爱￡侵袭症＋ 提交于 2019-11-30 20:46:32
1.首先下载RabbitMQ所需的erlang环境： http://www.erlang.org/downl 2.然后下载RabbitMQ： http://www.rabbitmq.com/download.html 下载rabbitmq-server-3.7.8.exe 然后安装即可。 确认开启RabbitMQ服务。 然后如果想要开启web页面，需要进入sbin目录然后运行rabbitmq-plugins enable rabbitmq_management命令： 访问 http://localhost:15672 账号 密码都是guest 在Admin中新增用户： 其中Tags是用户权限： none 1.不能访问 management plugin management：用户可以通过AMQP做的任何事外加 1.列出自己可以通过AMQP登入的virtual hosts 2.查看自己的virtual hosts中的queues, exchanges 和 bindings 3.查看和关闭自己的channels 和 connections 4.查看有关自己的virtual hosts的“全局”的统计信息，包含其他用户在这些virtual hosts中的活动 policymaker：management可以做的任何事外加： 1.查看、创建和删除自己的virtual

Alternatives to vtable

由 巧了我就是萌 提交于 2019-11-30 20:17:08
Vtables are ubiquitous in most OO implementations, but do they have alternatives? The wiki page for vtables has a short blurb, but not really to much info (and stubbed links). Do you know of some language implementation which does not use vtables? Are there are free online pages which discuss the alternatives? Yes, there are many alternatives! Vtables are only possible when two conditions hold. All method calls can be determined statically. If you can call functions by string name, or if you have no type information about what objects you are calling methods on, you can't use vtables because
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