C++学习笔记基础篇29——多态性与虚函数

虚函数

使用基类之指针，指向派生类的对象，调用虚函数的时候，最后调用的是派生类的函数！

程序1虚函数使用举例

#include <iostream> #include <string> using namespace std; enum EStudentType { EStudentType_Error = 0, EStudentType_Xiao = 1, EStudentType_Zhong = 2, }; class CStudent { public: char *p_name; char sex; int num; int age; static int master; EStudentType type; virtual void shangke() { cout << "CStudent" << endl; } CStudent(){ type = EStudentType_Error; }; CStudent(char* pname, char t_sex, int t_num, int t_age) :sex(t_sex), num(t_num), age(t_age) { type = EStudentType_Error; p_name = NULL; int n_len = 0; if (pname) { n_len = strlen(pname); } if (n_len > 0) { p_name = new char[n_len + 1]; memset(p_name, 0, n_len + 1); strcpy(p_name, pname); } } CStudent(const CStudent& stud) { type = EStudentType_Error; int n_len = 0; n_len = strlen(stud.p_name); p_name = new char[n_len + 1]; memset(p_name, 0, n_len + 1); strcpy(p_name, stud.p_name); num = stud.num; age = stud.age; sex = stud.sex; } CStudent& operator=(const CStudent& stud) { type = EStudentType_Error; int n_len = 0; n_len = strlen(stud.p_name); p_name = new char[n_len + 1]; memset(p_name, 0, n_len + 1); strcpy(p_name, stud.p_name); num = stud.num; age = stud.age; sex = stud.sex; return *this; } bool operator==(const CStudent& stud) { int n_len = 0; n_len = strlen(stud.p_name); if ((num == stud.num) && (age == stud.age) && (sex == stud.sex) && (*p_name == *stud.p_name)) { for (int i = 0; i < n_len;i++) { if (*(p_name+i )!= *(stud.p_name+i)) { return false; } } return true; } else { return false; } } ~CStudent(); }; CStudent::~CStudent() { if (p_name) { delete[] p_name; p_name = NULL; } } int CStudent::master = 0; class CXiaoStudent : public CStudent { public: int yuwen_score; int shuxue_score; int english_score; void shangke() { cout << "CXiaoStudent" << endl; } CXiaoStudent() : CStudent("zhangsan", 'm', 1001, 20) { yuwen_score = 2; shuxue_score = 0; english_score = 0; type = EStudentType_Xiao; } ~CXiaoStudent() { cout <<"析构了" << endl; } }; class CZhongStudent : public CXiaoStudent { public: int wuli_score; int huaxue_score; void shangke() { cout << "CZhongStudent" << endl; } CZhongStudent() { type = EStudentType_Zhong; wuli_score = 0; huaxue_score = 0; } ~CZhongStudent() { cout << "析构了" << endl; } }; void average_age(CStudent* p_arr_stud, int n_size) { if (!p_arr_stud || n_size <= 0) return; int total_age = 0; EStudentType type = p_arr_stud[0].type; for (int idx = 0; idx < n_size; ++idx) { switch (type) { case EStudentType_Xiao: total_age += ((CXiaoStudent*)p_arr_stud)[idx].age; break; case EStudentType_Zhong: total_age += ((CZhongStudent*)p_arr_stud)[idx].age; break; default: break; } } int aver_age = total_age / n_size; switch (type) { case EStudentType_Xiao: cout << "小学生的平均年龄是：" << aver_age << endl; break; case EStudentType_Zhong: cout << "中学生的平均年龄是：" << aver_age << endl; break; default: break; } } int main(int argc, char* argv[]) { CZhongStudent stud_zhong; stud_zhong.shangke(); CStudent *pStud = &stud_zhong; pStud->shangke(); system("pause"); return 0; }

例子2不同的狗

#include<iostream>; using namespace std; class CDog { public: int num; virtual void wangwang() { cout << "wangwang"<< endl; } CDog(){}; ~CDog(){ cout << "CDong析构了" << endl; }; }; class jinmao :public CDog { public: void wangwang() { cout << "jinmaowangwang" << endl; } jinmao(){}; ~jinmao(){ cout << "jinmao析构了" << endl; }; }; class jiwawa :public CDog { public: void wangwang() { cout << "jiwawawangwang" << endl; } jiwawa(){}; ~jiwawa(){ cout << "jiwawa析构了" << endl; }; }; class zhangao :public CDog { public: void wangwang() { cout << "zhangaowangwang" << endl; } zhangao(){}; ~zhangao(){ cout << "zhangao析构了" << endl; }; }; int main(int argc,char* argv[]) { jinmao wang1; wang1.wangwang(); jiwawa wang2; wang2.wangwang(); zhangao wang3; wang3.wangwang(); CDog* Pwang1; Pwang1 = &wang1; Pwang1->wangwang(); CDog* Pwang2; Pwang2 = &wang2; Pwang2->wangwang(); CDog* Pwang3; Pwang3 = &wang3; Pwang3->wangwang(); system("pause"); return 0; }