C++类的特性相关题目

https://blog.csdn.net/akof1314/article/details/7520034

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#include <iostream>
using namespace std;

class A
{
public:
    int _a;
    A()
    {
        _a = 1;
    }
    void print()
    {
        printf("%d\n", _a);
    }
};

class B: public A
{
public:
    int _a;
    B()
    {
        _a = 2;
    }
};

int main()
{
    B b;
    b.print();
    printf("%d\n", b._a);
    return 0;
}

输出：

1
2

子类覆盖父类的变量。

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#include <iostream>
using namespace std;

class base
{
private:
    int m_i;
    int m_j;
public:
    base(int i):m_j(i),m_i(m_j){}
    base():m_j(0),m_i(m_j){}
    int get_i(){return m_i;}
    int get_j(){return m_j;}
};

int main()
{
    base obj(98);
    cout<<obj.get_i()<<endl
        <<obj.get_j()<<endl;
    return 0;
}

输出：

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2

-858993460
98

构造函数的初始化变量顺序是按照成员变量的声明顺序来执行的。

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#include <iostream>
using namespace std;

class B
{
private:
    int data;
public:
    B()
    {
        cout<<"default constructor"<<endl;
    }
    ~B()
    {
        cout<<"destructed"<<endl;
    }
    B(int i):data(i)
    {
        cout<<"constructor by parameter"<<data<<endl;
    }
};

B Play(B b)
{
    return b;
}

int main()
{
    B temp = Play(5);
    return 0;
}

输出：

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3

constructor by parameter5
destructed
destructed

Play(5)通过隐含类型转换调用B:B(int i)，返回时调用析构函数，temp调用拷贝构造函数。

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#include <iostream>
using namespace std;

class CA
{
public:
    void f()
    {
        cout << "CA f()" << endl;
    }
    virtual void ff()
    {
        cout << "CA ff()" << endl;
        f();
    }
};

class CB : public CA
{
public :
    virtual void f()
    {
        cout << "CB f()" << endl;
    }
    void ff()
    {
        cout << "CB ff()" << endl;
        f();
        CA::ff();
    }
};
class CC : public CB
{
public:
    virtual void f()
    {
        cout << "C f()" << endl;
    }
};

int main()
{
    CB b;
    CA *ap = &b;
    CC c;
    CB &br = c;
    CB *bp = &c;

    ap->f();
    cout << endl;

    b.f();
    cout << endl;

    br.f();
    cout << endl;

    bp->f();
    cout << endl;

    ap->ff();
    cout << endl;

    bp->ff();
    cout << endl;

    return 0;
}

输出：

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CA f()

CB f()

C f()

C f()

CB ff()
CB f()
CA ff()
CA f()

CB ff()
C f()
CA ff()
CA f()

指针和引用都能引发多态。

C++类的特性相关题目

C++类的特性相关题目

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