umimplemented pure virtual method 中文解释，并且举例

未实现的纯虚方法（unimplemented pure virtual method）是指在基类中声明的纯虚方法，但在派生类中没有实现的方法。纯虚方法是在基类中声明的方法，但是没有实现的方法，它们只是一个接口，需要在派生类中进行实现。

举例来说，假设我们有一个基类Animal，其中有一个纯虚方法speak()：

class Animal{
  public:
    virtual void speak() = 0; //纯虚方法
};

然后我们派生出两个类Dog和Cat：

class Dog : public Animal{
  public:
    void bark(){ cout << "Woof!" << endl; }
};

class Cat : public Animal{
  public:
    void meow(){ cout << "Meow!" << endl; }
};

在这个例子中，派生类Dog和Cat都没有实现基类Animal中的纯虚方法speak()，因此它们仍然是抽象类，不能实例化。如果我们尝试实例化它们，编译器会报错。

相关问题

umimplemented pure virtual method

An unimplemented pure virtual method is a method in a C++ class that is declared as pure virtual, but not implemented in the class. A pure virtual method is a virtual function that does not have any implementation in the base class, and its implementation is provided by the derived class. When a pure virtual method is not implemented in a derived class, it remains unimplemented, and the derived class becomes an abstract class.

An abstract class cannot be instantiated, and it should be used as a base class for other classes that provide the implementation for the pure virtual methods. If a class contains an unimplemented pure virtual method, the compiler will generate an error message, and the class cannot be instantiated.

For example, consider a class called Shape that has a pure virtual method called area():

class Shape {
public:
    virtual double area() const = 0; // pure virtual method
};

If a derived class, such as Circle, does not provide an implementation for the area() method, it will become an abstract class:

class Circle : public Shape {
public:
    // no implementation for area() method
};

The compiler will generate an error message because the Circle class is abstract and cannot be instantiated. To fix this error, the Circle class should provide an implementation for the area() method:

class Circle : public Shape {
public:
    double area() const override {
        return 3.14 * radius * radius;
    }
private:
    double radius;
};

Now the Circle class can be instantiated, and it provides its own implementation for the area() method.

pure virtual method called出现这个情况一般是什么

`pure virtual method called` 意味着一个纯虚函数被调用了。纯虚函数是一种在基类中声明但没有实现的虚函数，它的实现由派生类来完成。纯虚函数用 `= 0` 来标记，例如：

class Base {
public:
    virtual void foo() = 0; // 纯虚函数
};

class Derived : public Base {
public:
    void foo() override {
        std::cout << "Derived::foo()" << std::endl;
    }
};

int main() {
    Base* ptr = new Derived();
    ptr->foo(); // 输出 "Derived::foo()"
    delete ptr;
    return 0;
}

在上面的代码中，我们定义了一个基类 `Base`，其中声明了一个纯虚函数 `foo()`，并在派生类 `Derived` 中实现了该函数。在 `main()` 函数中，我们定义了一个基类指针 `ptr`，并将其指向一个派生类对象。我们调用了 `ptr` 的 `foo()` 函数，由于在派生类中已经实现了该函数，因此输出的是 "Derived::foo()"。

如果在派生类中没有实现纯虚函数，或者实现了但没有覆盖基类中的同名函数，则编译器会报错。如果在运行时调用了一个没有实现的纯虚函数，则会出现 `pure virtual method called` 的错误。这通常意味着程序中存在逻辑错误，需要检查代码并进行修复。