防止对象切片- c++
Preventing Object Slicing - C++
我正在尝试创建Person对象的矢量。但是，我真的想要存储从Person基类派生的Adult、Professor和Student对象。在问这个问题之后，我了解到我的问题是在对象拼接中，它会将派生类保存为Person类，因为这就是向量的含义。我试图修改代码来纠正这种情况，但我仍然遇到一些错误，需要一些额外的帮助。谢谢!
下面是我的main.cpp代码:#include "Person.h"
#include "Professor.h"
#include "Student.h"
#include "Adult.h"
#include <vector>
#include <string>
#include <iostream>
using namespace std;
template<typename T> void addPerson(vector<Person *> &personVector) {
cout << "DEBUG" << endl;
personVector.push_back(new T());
}
void addFriend(vector<Person *> &personVector) {
bool loop = true;
while (loop) {
cout << "nWhich Person would you like to create? " << endl;
cout << " 1. Professor" << endl;
cout << " 2. Student" << endl;
cout << " 3. Adult" << endl;
int caseVar;
cin >> caseVar;
switch (caseVar) {
case 1:
addPerson<Professor>(personVector);
// old incorrect line: addPerson<Professor *>(personVector);
loop = false;
break;
case 2:
addPerson<Student>(personVector);
// old incorrect line: addPerson<Student *>(personVector);
loop = false;
break;
case 3:
addPerson<Adult>(personVector);
// old incorrect line: addPerson<Adult *>(personVector);
loop = false;
break;
default: cout << "Unknown Entry Please Try Again." << endl;
}
}
}
void displayFriends(vector<Person *> &personVector) {
if (personVector.size() > 1) {
for (unsigned i = 0; personVector.size() > i; i++)
cout << i+1 << ". " << personVector[i]->getName() << endl;
cout << "DEBUG" << endl;
}
}
void viewFriend(vector<Person *> &personVector) {
if (personVector.size() > 1) {
displayFriends(personVector);
cout << "Which # friend would you like to view? ";
int num;
cin >> num;
personVector[num-1]->coutPerson();
} else if (personVector.size() == 1) {
personVector[0]->coutPerson();
} else {
cout << "No friends to View." << endl;
}
}
void deleteElementFromArray(int element, vector<Person *> &personVector) {
vector<Person *> newPersonVector;
for (unsigned i = 0; personVector.size() > i; i++)
if (i != element - 1)
newPersonVector.push_back(personVector[i]);
personVector = newPersonVector;
}
void removeFriend(vector<Person *> &personVector) {
if (personVector.size() > 1) {
displayFriends(personVector);
cout << "Which # friend would you like to remove? ";
unsigned num;
cin >> num;
if (num <= personVector.size())
deleteElementFromArray(num, personVector);
else
cout << "Invalid Selection" << endl;
} else if (personVector.size() == 1) {
cout << "Removed one and only friend" << endl;
} else {
cout << "No friends to Remove." << endl;
}
}
int main() {
vector<Person *> personVector;
// Run Main Menu
cout << "Friends with Stuff" << endl;
cout << "Adding 5 friends to the list" << endl;
personVector.push_back(new Person("James"));
personVector.push_back(new Person("Martin"));
personVector.push_back(new Person("Sammi"));
personVector.push_back(new Person("Donny"));
personVector.push_back(new Person("Ronald"));
bool loop = true;
while (loop) {
cout << "nWhat would you like to do? " << endl;
cout << " 1. Add New Friend" << endl;
cout << " 2. View Friend" << endl;
cout << " 3. Remove Friend" << endl;
cout << " 4. Clear Friends" << endl;
cout << " 5. Get Object" << endl;
cout << " 6. Exit" << endl;
int caseVar;
cin >> caseVar;
switch (caseVar) {
case 1:
addFriend(personVector);
break;
case 2:
viewFriend(personVector);
break;
case 3:
removeFriend(personVector);
break;
case 4:
personVector.clear();
break;
case 5:
break;
case 6:
loop = false;
break;
default: cout << "Unknown Entry Please Try Again." << endl;
}
}
}
我得到以下错误
InitializeBuildStatus:
1> Touching "DebugFPVisualStudio.unsuccessfulbuild".
1>ClCompile:
1> main.cpp
1>\cs1cs_studentsmlindahl15cs172final projectfpvisualstudiomain.cpp(12): error C2664: 'void std::vector<_Ty>::push_back(_Ty &&)' : cannot convert parameter 1 from 'Professor **' to 'Person *&&'
1> with
1> [
1> _Ty=Person *
1> ]
1> Reason: cannot convert from 'Professor **' to 'Person *'
1> Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
1> \cs1cs_studentsmlindahl15cs172final projectfpvisualstudiomain.cpp(26) : see reference to function template instantiation 'void addPerson<Professor*>(std::vector<_Ty>)' being compiled
1> with
1> [
1> _Ty=Person *
1> ]
1>\cs1cs_studentsmlindahl15cs172final projectfpvisualstudiomain.cpp(12): error C2664: 'void std::vector<_Ty>::push_back(_Ty &&)' : cannot convert parameter 1 from 'Student **' to 'Person *&&'
1> with
1> [
1> _Ty=Person *
1> ]
1> Reason: cannot convert from 'Student **' to 'Person *'
1> Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
1> \cs1cs_studentsmlindahl15cs172final projectfpvisualstudiomain.cpp(30) : see reference to function template instantiation 'void addPerson<Student*>(std::vector<_Ty>)' being compiled
1> with
1> [
1> _Ty=Person *
1> ]
1>\cs1cs_studentsmlindahl15cs172final projectfpvisualstudiomain.cpp(12): error C2664: 'void std::vector<_Ty>::push_back(_Ty &&)' : cannot convert parameter 1 from 'Adult **' to 'Person *&&'
1> with
1> [
1> _Ty=Person *
1> ]
1> Reason: cannot convert from 'Adult **' to 'Person *'
1> Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
1> \cs1cs_studentsmlindahl15cs172final projectfpvisualstudiomain.cpp(34) : see reference to function template instantiation 'void addPerson<Adult*>(std::vector<_Ty>)' being compiled
1> with
1> [
1> _Ty=Person *
1> ]
1>
1>Build FAILED.
1>
1>Time Elapsed 00:00:02.90
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
我相信它是在告诉我代码中有太多的指针。然而，我不明白为什么会这样。我唯一有指针的地方是说向量包含了我需要在每种情况下重复的东西。这些指针是必需的所以我没有对象切片
Person.h
#ifndef PERSON_H
#define PERSON_H
#include <string>
#include "Date.h"
#include "PhoneNumber.h"
using namespace std;
class Person
{
protected:
string name;
Date birthday;
PhoneNumber phoneNumber;
string city, state;
public:
// Constructors
Person();
Person(string name) {
this->name = name;
birthday = Date();
phoneNumber = PhoneNumber("0000000000");
city = "Unknown";
state = "Unknown";
}
// Getter and Setter Methods
string getName();
void setName(string);
Date getBirthday();
// Methods
void coutPerson();
};
#endif
Person.cpp
#include "Person.h"
#include "PhoneNumber.h"
#include "Date.h"
#include <string>
#include <iostream>
using namespace std;
// Constructors
Person::Person() {
cin.ignore();
cout << "Name? ";
getline(cin, name);
cout << "Birthday: " << endl;
birthday.askUserForDate();
phoneNumber.create();
cout << "City? ";
getline(cin, city);
cout << "State? ";
getline(cin, state);
}
// Getter and Setter Methods
string Person::getName() {
return name;
}
void Person::setName(string name) {
this->name = name;
}
void Person::coutPerson() {
cout << name << endl;
birthday.coutDate();
phoneNumber.coutPhoneNumber();
cout << city << ", " << state << endl;
}
// Methods
Student.h
#ifndef STUDENT_H
#define STUDENT_H
#include "Person.h"
using namespace std;
class Student : public Person
{
private:
string dorm;
int dormRoom;
public:
// Constructors
Student();
Student(Student &);
// Getter and Setter Methods
// Methods
void coutPerson();
};
#endif
Student.cpp
#include "Student.h"
#include "Person.h"
#include <string>
#include <iostream>
using namespace std;
// Constructors
Student::Student() {
cin.ignore();
cout << "Dorm? ";
getline(cin, dorm);
cout << "Dorm Room #? ";
cin >> dormRoom;
}
// TODO Copy Constructors
// TODO Deconstructors
// Overload < > ==
Student::Student(Student &student) {
Person::Person(student);
dorm = student.dorm;
dormRoom = student.dormRoom;
}
void Student::coutPerson() {
cout << "DEBUG: Student::coutPerson()" << endl;
Person::coutPerson();
cout << "Dorm Room: " << this->dorm << " " << this->dormRoom << endl;
}
// Methods
你的模板参数是指针，但不应该因为在你的方法中，例如template<typename T> void addPerson(...)，你使用new创建了T的新实例，因此你创建了一个指向一个人的新指针(即new Person*()，这将导致Person***)。
因此，只需将其命名为:addPerson<Professor>(personVector);，它将将new T()转换为new Professor()，从而产生Professor*结果。
void deleteElementFromArray(int element, vector<Person *> personVector) {
vector<Person *> newPersonVector;
for (unsigned i = 0; personVector.size() > i; i++)
if (i != element - 1)
newPersonVector.push_back(personVector[i]);
personVector = newPersonVector;
}
首先，你要删除element - 1，所以要注意你不能传递0(即element在这里是一个基于1的索引)。
第二，将newPersonVector赋值给参数personVector。然而，由于你是按值传递向量(它是复制的)，这个变化在函数之外是不可见的。
你有几个解决方案:
- 删除
personVector中的条目，而不是复制不应该删除的条目。使用personVector.erase(personVector.begin() + element)之类的东西(注意这里的语法可能不太正确，但您应该得到它)。 - 传递指向向量的指针:
void deleteElementFromArray(int element, vector<Person *>* personVector) - 返回新向量并替换旧向量。这样调用就变成了
personVector = removeFriend(personVector);
我个人更喜欢选项1，因为它重用vector，从而减少了复制操作。
您需要删除模板参数中的*。
addPerson<Professor *>(personVector);
取代:
addPerson<Professor>(personVector);
当前，你正在创建一个Professor ** .
更新:并且在您的main()中，您应该使用new Person("Name")创建人员，您现在使用的没有意义，即"获取此类型的地址"正在工作，但这是一个非常糟糕的主意(获取在堆栈上创建的对象的地址)。
personVector.push_back(&Person("James"));
取代:
personVector.push_back(new Person("James"));
Update2:请注意，您负责在某些时候释放您以这种方式分配的内存。
代码
addPerson<Professor *>(personVector);
尝试修改为:
addPerson<Professor>(personVector);
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