C++继承方式
2022/2/20 22:29:17
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C++类成员访问属性
类成员的访问属性有3种,公有属性,保护属性,私有属性。
其中公有属性的成员在类内和类外均可以直接访问;
保护属性的成员在类内可以访问,类外不可直接访问;
私有属性的成员在类内可以访问,类外不可直接访问;
举例:
类内:
1 class A 2 { 3 private: 4 int a; 5 protected: 6 int b; 7 public: 8 int c; 9 void PrintName() { 10 //3个数据成员在类内均可直接访问 11 cout << a << endl; 12 cout << b << endl; 13 cout << c << endl; 14 } 15 };
类外:
1 int main() 2 { 3 A Object; 4 cout << Object.a << endl; //私有不可直接访问,member "A::a" (declared at line 72) is inaccessible 5 cout << Object.b << endl; //保护不可直接访问,member "A::b" (declared at line 72) is inaccessible 6 cout << Object.c << endl; //公有可以直接访问 7 8 return EXIT_SUCCESS; 9 }
C++继承方式
C++类的继承方式有3种,公有继承(public)、保护继承(protected)、私有继承(private)。
1.公有继承
采用公有继承方式创建的子类,基类中的私有成员对子类来说是不可见的,不能直接访问;基类的保护成员在子类中的访问属性还是protected,基类的公有成员在子类中的访问属性还是public。
在子类中可以直接访问基类的保护和公有成员,但是在类外不可直接访问基类的保护成员。
1 class People 2 { 3 private: 4 int a; //私有成员 5 protected: 6 int b; //保护成员 7 public: 8 int c; //公有成员 9 }; 10 11 /** 12 * 公有继承,基类中的私有成员在子类中不可见,保护成员属性还是保护成员,共有成员属性还是公有成员 13 */ 14 class PublicDerive : public People 15 { 16 void printName() { 17 cout << a << endl; //基类私有不可见,member "People::a" (declared at line 8) is inaccessible 18 cout << b << endl; //基类保护,类内可见,属性保护 19 cout << c << endl; //基类公有,类内可见,属性公有 20 } 21 }; 22 23 int main() 24 { 25 PublicDerive publicDerive; 26 cout << publicDerive.a << endl; //member "People::a" (declared at line 8) is inaccessible 27 cout << publicDerive.b << endl; //member "People::b" (declared at line 10) is inaccessible 28 cout << publicDerive.c << endl; // 29 30 return EXIT_SUCCESS; 31 }
2.保护继承
采用保护继承方式创建的子类,基类中的私有成员对子类来说是不可见的,不可直接访问,基类的保护成员和公共成员在子类中的属性均是protected。
1 class People 2 { 3 private: 4 int a; //私有成员 5 protected: 6 int b; //保护成员 7 public: 8 int c; //公有成员 9 }; 10 11 class ProtectedDerive : protected People 12 { 13 void printName() { 14 cout << a << endl; //基类私有不可见,'People::a': cannot access private member declared in class 'People' 15 cout << b << endl; //基类保护,类内可见,属性保护 16 cout << c << endl; //基类公有,类内可见,属性保护 17 } 18 }; 19 20 int main() 21 { 22 ProtectedDerive protectedDerive; 23 cout << protectedDerive.a << endl; //'People::a': cannot access private member declared in class 'People' 24 cout << protectedDerive.b << endl; //'People::b': cannot access protected member declared in class 'People' 25 cout << protectedDerive.c << endl; //'People::c' not accessible because 'ProtectedDerive' uses 'protected' to inherit from 'People' 26 27 return EXIT_SUCCESS; 28 }
如上代码中,ProtectedDerive中成员b和c的访问属性还不能直观说明,因为类内均可直接访问,类外均不能访问,说明bc属性是保护或者私有。可用如下方式进行验证:
1 class ProtectedDerive2 : public ProtectedDerive 2 { 3 void printName() { 4 cout << a << endl; //基类私有不可见,'People::a': cannot access private member declared in class 'People' 5 cout << b << endl; //基类保护,类内可见,属性保护 6 cout << c << endl; //基类保护,类内可见,属性保护 7 } 8 };
ProtectedDerive2类从ProtectedDerive类继承而来,但是bc属性在ProtectedDerive2类内是可见的。因私有继承,基类属性在子类中不可见,所以保护继承方式中,基类的保护和公有属性在子类中的属性是保护。
3.私有继承
采用私有继承方式创建的子类,基类中的私有成员对子类来说不可见,不可直接访问,保护和公共成员在子类中的属性均为private。
1 class People 2 { 3 private: 4 int a; //私有成员 5 protected: 6 int b; //保护成员 7 public: 8 int c; //公有成员 9 }; 10 11 class PrivateDerive : private People 12 { 13 void printName() 14 { 15 cout << a << endl; //基类私有不可见 16 cout << b << endl; //基类保护,类内可见,属性私有 17 cout << c << endl; //基类公有,类内可见,属性私有 18 } 19 }; 20 21 int main() 22 { 23 24 PrivateDerive privateDerive; 25 cout << privateDerive.a << endl; //'People::a': cannot access private member declared in class 'People' 26 cout << privateDerive.b << endl; //'People::b': cannot access protected member declared in class 'People' 27 cout << privateDerive.c << endl; //'People::c' not accessible because 'ProtectedDerive' uses 'protected' to inherit from 'People' 28 29 return EXIT_SUCCESS; 30 }
如上方式可以知道在子类PrivateDerive中,bc成员可在子类内直接访问,不可在子类外直接访问,其属性为保护或者私有。采用如下方式验证属性:
1 class PrivateDerive2 : public PrivateDerive 2 { 3 void printName() { 4 cout << a << endl; //基类私有,不可见,'People::a': cannot access private member declared in class 'People' 5 cout << b << endl; //基类私有,不可见,'People::b': cannot access inaccessible member declared in class 'People' 6 cout << c << endl; //基类私有,不可见,'People::c' not accessible because 'ProtectedDerive' uses 'private' to inherit from 'People' 7 } 8 };
PrivateDerive2类从PrivateDerive类继承而来,a/b/c三个属性均不可直接在类内访问,说明PrivateDerive的三个属性均是私有。
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