C++ 纯虚函数也是可以实现的

class PureVirtualA {

public:

    virtual ~PureVirtualA();

    virtual void testPureVirtualFunc() = 0;

protected:

    void publicFunc();

};

PureVirtualA::~PureVirtualA()

{

}

void PureVirtualA::publicFunc()

{

    std::cout << "PureVirtualA::publicFunc()" << std::endl;

}



void PureVirtualA::testPureVirtualFunc() {

    std::cout << "PureVirtualA::testPureVirtualFunc()" << std::endl;

}



class TestB : public PureVirtualA {

public:

    void testPureVirtualFunc();

};

void TestB::testPureVirtualFunc() {

    PureVirtualA::testPureVirtualFunc();

    std::cout << "B::testPureVirtualFunc()" << std::endl;

    this->publicFunc();

}

// ... 测试

PureVirtualA* test = new TestB;
test->testPureVirtualFunc();

test->PureVirtualA::testPureVirtualFunc();

默认的实现可以像 publicFunc 一样用于公共的方法来使用
这种方法的好处是少了一个需要维护的函数，缺点是客户代码可以直接调用基类的缺省实现。

// 测试输出：

PureVirtualA::testPureVirtualFunc()
B::testPureVirtualFunc()
PureVirtualA::publicFunc()
PureVirtualA::testPureVirtualFunc()