如果我要覆盖它,我可以调用基类的虚函数吗？

Question

假设我有课程Foo并Bar设置如下:

class Foo
{
public:
    int x;

    virtual void printStuff()
    {
        std::cout << x << std::endl;
    }
};

class Bar : public Foo
{
public:
    int y;

    void printStuff()
    {
        // I would like to call Foo.printStuff() here...
        std::cout << y << std::endl;
    }
};

正如在代码中注释的那样,我希望能够调用我所覆盖的基类函数.在Java中有super.funcname()语法.这在C++中是否可行？

Answer 1

C++语法是这样的:

class Bar : public Foo {
  // ...

  void printStuff() {
    Foo::printStuff(); // calls base class' function
  }
};

Answer 2

是,

class Bar : public Foo
{
    ...

    void printStuff()
    {
        Foo::printStuff();
    }
};

它与superJava中的相同,只是它允许在具有多个继承时从不同的基础调用实现.

class Foo {
public:
    virtual void foo() {
        ...
    }
};

class Baz {
public:
    virtual void foo() {
        ...
    }
};

class Bar : public Foo, public Baz {
public:
    virtual void foo() {
        // Choose one, or even call both if you need to.
        Foo::foo();
        Baz::foo();
    }
};

Answer 3

有时你需要调用基类的实现,当你不在派生函数中时...它仍然有效:

struct Base
{
    virtual int Foo()
    {
        return -1;
    }
};

struct Derived : public Base
{
    virtual int Foo()
    {
        return -2;
    }
};

int main(int argc, char* argv[])
{
    Base *x = new Derived;

    ASSERT(-2 == x->Foo());

    //syntax is trippy but it works
    ASSERT(-1 == x->Base::Foo());

    return 0;
}

Answer 4

为了防止你为你班上的很多功能做到这一点:

class Foo {
public:
  virtual void f1() {
    // ...
  }
  virtual void f2() {
    // ...
  }
  //...
};

class Bar : public Foo {
private:
  typedef Foo super;
public:
  void f1() {
    super::f1();
  }
};

如果要重命名Foo,这可能会节省一些写入.

Answer 5

如果要从派生类中调用基类函数,只需在提取基类名称(如Foo :: printStuff())时调用重写函数.

代码在这里

#include <iostream>
using namespace std;

class Foo
{
public:
    int x;

    virtual void printStuff()
    {
         cout<<"Base Foo printStuff called"<<endl;
    }
};

class Bar : public Foo
{
public:
    int y;

    void printStuff()
    {
        cout<<"derived Bar printStuff called"<<endl;
        Foo::printStuff();/////also called the base class method
    }
};

int main()
{
    Bar *b=new Bar;
    b->printStuff();
}

同样,您可以在运行时确定使用该类的对象(派生或基础)调用哪个函数.但这要求您在基类中的函数必须标记为虚拟.

代码如下

#include <iostream>
using namespace std;

class Foo
{
public:
    int x;

    virtual void printStuff()
    {
         cout<<"Base Foo printStuff called"<<endl;
    }
};

class Bar : public Foo
{
public:
    int y;

    void printStuff()
    {
        cout<<"derived Bar printStuff called"<<endl;
    }
};

int main()
{

    Foo *foo=new Foo;
    foo->printStuff();/////this call the base function
    foo=new Bar;
    foo->printStuff();
}