c++ - 基本深拷贝(操作重载)

Question

我正在制作一个简单的类 Person，它继承自抽象类 Object。我正处于学习深拷贝的部分，但我似乎无法让这段简单的代码工作:

Person.h

#include <iostream>
#include <cstring>  
#ifndef _PERSON_H_
#define _PERSON_H_
using namespace std;


class Object {
protected:
    //This pure virtual func. sends appropriate  ostream
    //to operator<<'s override. Must be implemented in each
    //derived class accordingly.
    virtual void print(std::ostream&) const =0;
public:
    //Override ostream operator.
    friend ostream& operator<<(ostream& os, const Object& obj);
    friend ostream& operator<<(ostream& os, const Object* obj);
    virtual ~Object();
};

class Person : public Object {
private:
    char* m_name;
    virtual void print(std::ostream& os) const;
    Person(); //What's your default name?
public:
    Person(char* name);
    Person(const Person& p);
    Person& operator=(const Person &rhs);
    virtual ~Person();
};

#endif // _PERSON_H_

Person.cpp

#include "Person.h"


ostream& operator<<(ostream& os, const Object& obj) {
    obj.print(os);
    return os;
}

ostream& operator<<(ostream& os, const Object* obj) {
    obj->print(os);
    return os;
}
Object::~Object() { };

//Standard ctor
Person::Person(char* name) {
    m_name = new char[strlen(name)];
    strncpy(m_name, name, strlen(name));
}
//Copy ctor
Person::Person(const Person& p) {
    m_name = new char[strlen(p.m_name)];
    strncpy(m_name, p.m_name, strlen(p.m_name));
}


//dtor
Person::~Person() {
    delete [] m_name;
}
//operator= overload
Person& Person::operator=(const Person &rhs) {
    if (this == &rhs) return * this; //Self copy check.
    delete [] m_name;
    m_name = new char[strlen(rhs.m_name)];
    strncpy(m_name, rhs.m_name, strlen(rhs.m_name));
    return * this;
}

//private
void Person::print(std::ostream& os) const{
    os << m_name;
}

int main() {
    //Person p1("Anis");
    //Person p2("Bassam");
    Person * p1 = new Person("Anis");
    Person * p2 = new Person("Bassam");
    p1 = p2;
    delete p1; 
    delete p2;
    return 0;
}

输出:

a.out(4839,0x7fff7420b300) malloc: *** error for object 0x7f914b404ad0: pointer being freed was not allocated

gdb BT:

#0  0x00007fff8d7b2282 in __pthread_kill ()
#1  0x00007fff8b5fd4c3 in pthread_kill ()
#2  0x00007fff8e528b73 in abort ()
#3  0x00007fff83739937 in free ()
#4  0x0000000100000b51 in Person::~Person (this=0x1001048e0) at Person.cc:29
#5  0x0000000100000b85 in Person::~Person (this=0x1001048e0) at Person.cc:28
#6  0x0000000100000ba8 in Person::~Person (this=0x1001048e0) at Person.cc:28
#7  0x0000000100000e46 in main () at Person.cc:54

程序在 delete p2; 时崩溃，根据 gdb。在书中他们就这种情况警告了我们，所以我遵循了他们提供的修复方法，即重载 operator= 并确保有复制构造函数。 我错过了什么？提前致谢。

附注我目前只对深层复制问题感兴趣。模板和泛型将在后面的章节中介绍。

Answer 1

在p1=p2之后，两个变量都指向同一个对象。 delete p1 删除这个对象。所以 delete p2 再次尝试删除这个对象。

Operator= 在这里帮不了您，因为您分配的是指针，而不是对象。可能您需要 *p1 = *p2。