Is there anyway to make program to chk prime number without using flag?

#include <cstdio> struct Base { virtual void foo() = 0; }; void Base::foo() { puts("Base::foo"); } struct Derive: Base { virtual void foo() override; }; void Derive::foo() { this->Base::foo(); puts("Derive::foo"); } int main() { Base *base = new Derive{}; base->foo(); } Hi guys. I just learnt the pure virtual function can be defined outside a class. But, is there any scenario for this usage?

how can i write a program to check prime number between two number?

For example if you have an pure virtual destructor. Except that some class designers also want to give a default implementation.

#include <cstdio> struct Base { virtual void foo() = 0; }; void Base::foo() { puts("Base::foo"); } struct Derive: Base { virtual void foo() override; }; void Derive::foo() { this->Base::foo(); puts("Derive::foo"); } int main() { Base *base = new Derive{}; base->foo(); } Hi guys. I just learnt the pure virtual function can be defined outside a class. But, is there any scenario for this usage?

So I don't see the point for the legitimacy/allowing of implementing a pure virtual function for the base class outside the base class.

Yes. But why for a pure virtual function?

My concern is for the pure virtual function. For "pure virtual functions", my understanding is that, "The base class doesn't provide an implementation. You must implement them in the derived class."

Maybe there are a few situations where it's usefull that you have the freedom to do that, but you're right, I also think it goes against the idea of pure virtual functions

Anyway still I don't fully understand that sentence. 1. A virtual function declared in a class shall be defined, 2. or declared pure (10.4) in that class, 3. or both are all ub?

It means you can: 1. declare a function as virtual and give a definition of the virtual function; 2. declare a function as pure virtual and give no definition of it; 3. declare a function as pure virtual and also give a definition of it.

Ok so far understood ... but all of them ub?

because “no diagnostic is required” == ub?

My concern is for the pure virtual function. For "pure virtual functions", my understanding is that, "The base class doesn't provide an implementation. You must implement them in the derived class."

Pure virtual functions mark classes who contain them as "abstract class". It means that no objects of an abstract calss could be created, and we cannot use it as parameter types, as function return types, or as the type of an explicit conversion. As a result, we'll never have a chance to call virtual member functions declared in an abstract class from its object. On the other hand, since it's a pure virtual function and will defintely be overrided in dirved classes. In consquence, in most cases, impl of pure virtual function is useless. Therefore, we can declare a function as pure function and give no definition of it. But remember, there are two exceptions. 1. for pure virtual destructor, you'll have to provide a definition. 2. the member functions of the derived class are free to call the abstract base's pure virtual function using qualified function id (Base::some_pure_virtual_function()). In these two cases, definition of pure virtual function makes sense.

Pure virtual functions mark classes who contain them as "abstract class". It means that no objects of an abstract calss could be created, and we cannot use it as parameter types, as function return types, or as the type of an explicit conversion. As a result, we'll never have a chance to call virtual member functions declared in an abstract class from its object. On the other hand, since it's a pure virtual function and will defintely be overrided in dirved classes. In consquence, in most cases, impl of pure virtual function is useless. Therefore, we can declare a function as pure function and give no definition of it. But remember, there are two exceptions. 1. for pure virtual destructor, you'll have to provide a definition. 2. the member functions of the derived class are free to call the abstract base's pure virtual function using qualified function id (Base::some_pure_virtual_function()). In these two cases, definition of pure virtual function makes sense.

abstract class object type can not be used as parameter types but abstract class pointer type is ok.

the pointer type of object is binding in the execution period. you can think it is a unsigned int value that store the memory address of the object. when we call a virtual member function, it will search the virtual function map in the object memory. the virtual function map is constructed by the class construct function and destory by the destory function. It's the reason that we can't call virtual function in the construct function.

the pointer type of object is binding in the execution period. you can think it is a unsigned int value that store the memory address of the object. when we call a virtual member function, it will search the virtual function map in the object memory. the virtual function map is constructed by the class construct function and destory by the destory function. It's the reason that we can't call virtual function in the construct function.

To those of you who work as a developer: I had a little discussion with my co workers and they said "most developers don't program in ther free time cause they program enough at work". Do you guys work on own projects or contribute to OpenSource projects in your free time?

yes, programming is playing, to me.

python?

😂 Not actually a developer though ... generally I write algorithms and my colleagues do the implementation. But now I just wanna know more language details and try to write C++ code

Any one is golang developer?