我可以在 C++ 类中使用 `abstract` 关键字吗
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/1298093/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Can I use `abstract` keyword in C++ class
提问by DevSolar
Can we write abstract keyword in C++ class?
我们可以在 C++ 类中编写抽象关键字吗？
回答by Ken
#define abstract
回答by DevSolar
No.
不。
Pure virtual functions, in C++, are declared as:
在 C++ 中，纯虚函数被声明为：
class X
{
public:
virtual void foo() = 0;
};
Any class having at least one of them is considered abstract.
任何至少具有其中之一的类都被认为是抽象的。
回答by Martin v. L?wis
No, C++ has no keyword abstract. However, you can write pure virtual functions; that's the C++ way of expressing abstract classes.
不，C++ 没有关键字抽象。但是，您可以编写纯虚函数；这就是 C++ 表达抽象类的方式。
回答by rahul
It is a keyword introduced as part of the C++/CLI language spefication for the .NET framework.
它是作为 .NET 框架的 C++/CLI 语言规范的一部分引入的关键字。
回答by Svetlozar Angelov
no, you need to have at least one pure virtual function in a class to be abstract.
不，你需要在一个类中至少有一个纯虚函数才能抽象。
Here is a good reference cplusplus.com
这是一个很好的参考cplusplus.com
回答by anorm
As others point out, if you add a pure virtual function, the class becomes abstract.
正如其他人指出的那样，如果您添加一个纯虚函数，该类就会变得抽象。
However, if you want to implement an abstract base class with no pure virtual members, I find it useful to make the constructor protected. This way, you force the user to subclass the ABC to use it.
然而，如果你想实现一个没有纯虚拟成员的抽象基类，我发现让构造函数受保护是很有用的。这样，您就可以强制用户对 ABC 进行子类化以使用它。
Example:
例子：
class Base
{
protected:
Base()
{
}
public:
void foo()
{
}
void bar()
{
}
};
class Child : public Base
{
public:
Child()
{
}
};
回答by Biedrzyk
actually keyword abstractexists in C++ (VS2010 at least) and I found it can be used to declare a class/struct as non-instantiated.
实际上关键字abstract存在于 C++（至少 VS2010）中，我发现它可以用来将类/结构声明为非实例化。
struct X abstract {
static int a;
static void foX(){};
};
int X::a = 0;
struct Y abstract : X { // something static
};
struct Z : X { // regular class
};
int main() {
X::foX();
Z Zobj;
X Xobj; // error C3622
}
MSDN: https://msdn.microsoft.com/en-us/library/b0z6b513%28v=vs.110%29.aspx
MSDN：https: //msdn.microsoft.com/en-us/library/b0z6b513%28v=vs.110%29.aspx
回答by Varun Kumar
No, you can't use abstract as a keyword because there is no such keyword available in C++.
不，您不能使用 abstract 作为关键字，因为 C++ 中没有这样的关键字。
If you want make a class as an in C++ abstract you can declare at least one function as pure virtual function.
如果你想在 C++ 中创建一个抽象类，你可以将至少一个函数声明为纯虚函数。
But in derived class you must provide definition else its give compilation error .
但是在派生类中，您必须提供定义，否则会出现编译错误。
Example:
例子：
class A
{
public:
virtual void sum () = 0;
};
note:
笔记：
You can used abstract as a variable name, class name because, as I told you, abstract is not a keyword in C++.
您可以将抽象用作变量名、类名，因为正如我告诉您的，抽象不是 C++ 中的关键字。
回答by Varun Kumar
No, C++ has no keyword abstract. However, you can write pure virtual functions; that's the C++ way of expressing abstract classes. It is a keyword introduced as part of the C++/CLI language spefication for the .NET framework. You need to have at least one pure virtual function in a class to be abstract.
不，C++ 没有关键字抽象。但是，您可以编写纯虚函数；这就是 C++ 表达抽象类的方式。它是作为 .NET 框架的 C++/CLI 语言规范的一部分引入的关键字。你需要在一个类中至少有一个纯虚函数才能成为抽象的。
class SomeClass {
public:
virtual void pure_virtual() = 0; // a pure virtual function
};
回答by Anoop Toffy
There is no keyword 'abstract' but a pure virtual function turns a class in to abstract class which one can extend and re use as an interface.
没有关键字“抽象”，但纯虚函数将类转换为抽象类，可以扩展并重新用作接口。
