C接口,继承,多态

发布时间：2020-12-16 06:53:25 所属栏目：百科来源：网络整理

导读：想象一下这种情况： interface I1：m1(),由C1类实现接口I2：m2(),由C2类实现 interface I3：m3(),由C3类实现我想定义带参数arg的函数. void f1(I1 arg) { use m1()}void f2([I1,I2] arg) { use m1() and m2()}void f3([I2,I3] arg) { use m2() and m3()}

想象一下这种情况：

> interface I1：m1(),由C1类实现
>接口I2：m2(),由C2类实现
> interface I3：m3(),由C3类实现

我想定义带参数arg的函数.

void f1(I1 arg) {
    use m1()
}

void f2([I1,I2] arg) {
    use m1() and m2()
}

void f3([I2,I3] arg) {
    use m2() and m3()
}

然后我想定义：

>一个“联合”接口I123,它具有所有方法,由C123实现
>“union”类C123,它继承现有类C1,C2,C3中的已实现方法.

然后我想实例化C123并将其与f1,f2,f3一起使用.

C123 obj;

f1(obj);
f2(obj);
f3(obj);

问题

>这可能在C？
>没有接口可以吗？例如.函数f2取[C1,C2]而不是[I1,I2].

代码

#include <string>
#include <iostream>

using namespace std;

class C1 {
protected:
  int i;
public:
  int getI() const { return i; }
  void setI(int i_) { i = i_; }
};

class C2 {
protected:
  string s;
public:
  string getS() const { return s; }
  void setS(string s_) { s = s_; }
};

class C3 {
protected:
  float f;
public:
  float getF() const { return f; }
  void setF(float f_) { f = f_; }
};

class C23 : public C2,public C3 {};
class C123 : public C1,public C2,public C3 {};

void f3(C23 arg) {
  arg.setS(to_string(arg.getF()));
}


int main() {

  C123 obj;

  f3(obj);

  std::cout << obj.getS();
}

错误消息

a.cc: In function ‘int main()’:
a.cc:42:9: error: could not convert ‘obj’ from ‘C123’ to ‘C23’
   f3(obj);

解决方法

Is this possible in C++?

是的,可以在C中做到这一点.

Example solution using interfaces

#include <string>
#include <iostream>

using namespace std;

class I1 {
public:
    virtual int getI() const = 0;
    virtual void setI(int i) = 0;
};

class I2 {
public:
    virtual string getS() const = 0;
    virtual void setS(string s) = 0;
};

class I3 {
public:
    virtual float getF() const = 0;
    virtual void setF(float f) = 0;
};

class C1 : public I1 {
protected:
    int i;
public:
    int getI() const { return i; }
    void setI(int i_) { i = i_; }
};

class C12 : public I1,public I2 {
protected:
    int i;
    string s;
public:
    int getI() const { return i; }
    void setI(int i_) { i = i_; }
    string getS() const { return s; }
    void setS(string s_) { s = s_; }
};

class C123 : public I1,public I2,public I3 {
protected:
    int i;
    string s;
    float f;
public:
    int getI() const { return i; }
    void setI(int i_) { i = i_; }
    string getS() const { return s; }
    void setS(string s_) { s = s_; }
    float getF() const { return f; }
    void setF(float f_) { f = f_; }
};

template<class T>
void f1(const T& c1)
{
    cout << "f1:n";
    cout << "  getI: " << c1.getI() << endl;
}

template<class T>
void f2(const T& c12)
{
    cout << "f2:n";
    cout << "  getI: " << c12.getI() << endl;
    cout << "  getS: " << c12.getS() << endl;
}

template<class T>
void f3(const T& c23)
{
    cout << "f3:n";
    cout << "  getS: " << c23.getS() << endl;
    cout << "  getF: " << c23.getF() << endl;
}

void test()
{
    C1 c1;
    c1.setI(1);
    f1(c1);

    cout << "n===== " << endl;

    C12 c12;
    c12.setI(12);
    c12.setS("str12");
    f1(c12);
    f2(c12);

    cout << "n===== " << endl;

    C123 c123;
    c123.setI(123);
    c123.setF(1.23f);
    c123.setS("str123");
    f1(c123);
    f2(c123);
    f3(c123);

    cout << "n===== " << endl;
}

int main()
{
    test();
}

Is it possible without interfaces? Eg. function f2 would take [C1,C2] instead of [I1,I2].

是的,没有接口就可以做到这一点.

Solution using virtual inheritance (without using interfaces)：

#include <string>
#include <iostream>

using namespace std;

class C1 {
protected:
    int i;
public:
    int getI() const { return i; }
    void setI(int i_) { i = i_; }
};

class C2 {
protected:
    string s;
public:
    string getS() const { return s; }
    void setS(string s_) { s = s_; }
};

class C3 {
protected:
    float f;
public:
    float getF() const { return f; }
    void setF(float f_) { f = f_; }
};

class C12 : public virtual C1,public virtual C2
{
};

class C23 : public virtual C2,public virtual C3
{
};

class C123 : public virtual C1,public virtual C12,public virtual C23
{
};


void f1(const C1& c1)
{
    cout << "f1:n";
    cout << "  getI: " << c1.getI() << endl;
}

void f2(const C12& c12)
{
    cout << "f2:n";
    cout << "  getI: " << c12.getI() << endl;
    cout << "  getS: " << c12.getS() << endl;
}

void f3(const C23& c23)
{
    cout << "f3:n";
    cout << "  getS: " << c23.getS() << endl;
    cout << "  getF: " << c23.getF() << endl;
}

void test()
{
    C1 c1;
    c1.setI(1);
    f1(c1);

    cout << "n===== " << endl;

    C12 c12;
    c12.setI(12);
    c12.setS("str12");
    f1(c12);
    f2(c12);

    cout << "n===== " << endl;

    C123 c123;
    c123.setI(123);
    c123.setF(1.23f);
    c123.setS("str123");
    f1(c123);
    f2(c123);
    f3(c123);

    cout << "n===== " << endl;
}

int main()
{
    test();
}

一些解释.如果你需要你的f2只采用C1和C2(没有C3)那么它必须是在C1和C2上都继承的单独类型. f3也是如此.然后,如果您遵循该逻辑并在不使用虚拟继承的情况下创建类C12和C23,那么现在应该从C12和C23继承的C123将以C2的多个副本结束,当您调用f2和f3时,您将获得不同的值GETS.虚拟继承确保继承层次结构中只有一个类的副本.

a “union” class C123 which inherits implemented methods from existing classes C1,C3

Solution that use virtual inheritance and interfaces

#include <string>
#include <iostream>

using namespace std;

class I1 {
public:
    virtual int getI() const = 0;
    virtual void setI(int i) = 0;
};

class I2 {
public:
    virtual string getS() const = 0;
    virtual void setS(string s) = 0;
};

class I3 {
public:
    virtual float getF() const = 0;
    virtual void setF(float f) = 0;
};

class I12 : virtual public I1,virtual public I2 {};
class I23 : virtual public I2,virtual public I3 {};
class I123 : virtual public I12,virtual public I23 {};

class C1 : virtual public I1 {
protected:
    int i;
public:
    int getI() const { return i; }
    void setI(int i_) { i = i_; }
};

class C2 : virtual public I2 {
protected:
    string s;
public:
    string getS() const { return s; }
    void setS(string s_) { s = s_; }
};

class C3 : virtual public I3 {
protected:
    float f;
public:
    float getF() const { return f; }
    void setF(float f_) { f = f_; }
};

class C12 : public I12,public C1,public C2 {};
class C123 : public I123,public C3 {};

void f1(const I1& c1)
{
    cout << "f1:n";
    cout << "  getI: " << c1.getI() << endl;
}

void f2(const I12& c12)
{
    cout << "f2:n";
    cout << "  getI: " << c12.getI() << endl;
    cout << "  getS: " << c12.getS() << endl;
}

void f3(const I123& c23)
{
    cout << "f3:n";
    cout << "  getS: " << c23.getS() << endl;
    cout << "  getF: " << c23.getF() << endl;
}

void test()
{
    C1 c1;
    c1.setI(1);
    f1(c1);

    cout << "n===== " << endl;

    C12 c12;
    c12.setI(12);
    c12.setS("str12");
    f1(c12);
    f2(c12);

    cout << "n===== " << endl;

    C123 c123;
    c123.setI(123);
    c123.setF(1.23f);
    c123.setS("str123");
    f1(c123);
    f2(c123);
    f3(c123);

    cout << "n===== " << endl;
}

int main()
{
    test();
}

所有解决方案都应产生此输出：

f1:
  getI: 1

=====
f1:
  getI: 12
f2:
  getI: 12
  getS: str12

=====
f1:
  getI: 123
f2:
  getI: 123
  getS: str123
f3:
  getS: str123
  getF: 1.23

=====

（编辑：李大同）

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