COUT打印后崩溃对象的getter

Question

基本上我的代码崩溃，我不能找出原因，我已经使用的代码:: Blocks的调试器，但对我来说没有任何帮助。它会在打印出属性的正确数据后崩溃[4]。我知道这不是实现这一目标的最佳方式，但是对于需要展示可以完成的多种方式的课程而言，我的问题是它显示“河桂餐厅”后崩溃，无法找出原因。

const int MAX_PROPERTIES = 5; 

int main(void) { 
    Property properties[MAX_PROPERTIES]; 
    Rentals tempRent; 

    tempRent = Rentals(); 
    tempRent.setBond(10000); 
    tempRent.setMonthlyRent(700); 

    tempRent.setOwner("River Kwai Restaurant"); 
    tempRent.setAddress("3 Bishopton Road"); 
    tempRent.setSuburb("Footscray"); 
    tempRent.setPostcode(5000); 

    properties[4] = tempRent; 
    tempRent.~Rentals(); 

    cout << properties[4].getOwner() << endl; 


    return 0; 
} 

Property::Property(){ 
    owner = "NULL"; 
    address = "NULL"; 
    suburb = "NULL"; 
    postcode = 0; 
} 

Property::Property(string theOwner, string theAddress, 
        string theSuburb, int thepostCode): 
        owner(theOwner), address(theAddress), 
        suburb(theSuburb), postcode(thepostCode){} 

Property::~Property() {} 

Rentals::Rentals(string theOwner, string theAddress, string theSuburb, 
        int thePostCode, double theBond, double theMonthlyRent): 
        Property(theOwner, theAddress, theSuburb, thePostCode), 
        bond(theBond), monthlyRent(theMonthlyRent){} 

Rentals::Rentals() : Property() { 
    owner = "NULL"; 
    address = "NULL"; 
    suburb = "NULL"; 
    postcode = 0; 
    bond = 0; 
    monthlyRent = 0; 
} 

Rentals::~Rentals() {} 

注：删除析构函数确实解决了它，但我想知道为什么？应该析构函数不会影响属性[4]，因为它已经被初始化了？

也就是说相关的代码，但我会后，如果需要下面的整个代码/头文件。

#include "property_a.h" 
#include "rentals.h" 
#include "commercial.h" 
#include "sales.h" 

const int MAX_PROPERTIES = 5; 

int main(void) { 
    Property properties[MAX_PROPERTIES]; 
    Rentals tempRent; 

    properties[0] = Commercial("Notting Hill McDonalds", 
           "4 Gardiner Road", "Notting Hill", 5000, 
           "Li3000"); 

    properties[1] = Rentals("Janet Dalgleish", "30 Firhill Court", 
          "Mary Hill", 4000, 500.00, 300.00); 

    properties[2] = Sales("Robert Burns", "3 Ayr Court", "Irvine", 4000, 
         "10/10/2015", 700000); 

    properties[3] = Property(); 
    properties[3] = properties[0]; 


    tempRent = Rentals(); 
    tempRent.setBond(10000); 
    tempRent.setMonthlyRent(700); 

    tempRent.setOwner("River Kwai Restaurant"); 
    tempRent.setAddress("3 Bishopton Road"); 
    tempRent.setSuburb("Footscray"); 
    tempRent.setPostcode(5000); 

    properties[4] = tempRent; 

    cout << properties[4].getOwner() << endl; 


    return 0; 
} 

Property::Property(){ 
    owner = "NULL"; 
    address = "NULL"; 
    suburb = "NULL"; 
    postcode = 0; 
} 

Property::Property(string theOwner, string theAddress, 
        string theSuburb, int thepostCode): 
        owner(theOwner), address(theAddress), 
        suburb(theSuburb), postcode(thepostCode){} 

Property::~Property() {} 

Commercial::Commercial() : Property() { 
    owner = "NULL"; 
    address = "NULL"; 
    suburb = "NULL"; 
    postcode = 0; 
    license = "NULL"; 
} 

Commercial::Commercial(string theOwner, string theAddress, 
         string theSuburb, int thepostCode, 
         string theLicense): Property(theOwner, theAddress, 
         theSuburb, thepostCode), license(theLicense) {} 

Commercial::~Commercial() {} 

Rentals::Rentals(string theOwner, string theAddress, string theSuburb, 
        int thePostCode, double theBond, double theMonthlyRent): 
        Property(theOwner, theAddress, theSuburb, thePostCode), 
        bond(theBond), monthlyRent(theMonthlyRent){} 

Rentals::Rentals() : Property() { 
    owner = "NULL"; 
    address = "NULL"; 
    suburb = "NULL"; 
    postcode = 0; 
    bond = 0; 
    monthlyRent = 0; 
} 

Rentals::~Rentals() {} 

Sales::Sales(string theOwner, string theAddress, string theSuburb, 
       int thepostCode, string theAuctionDate, double thePrice): 
       Property(theOwner, theAddress, theSuburb, thepostCode), 
       auctionDate(theAuctionDate), price(thePrice) {} 

Sales::Sales() : Property() { 
    owner = "NULL"; 
    address = "NULL"; 
    suburb = "NULL"; 
    postcode = 0; 
    auctionDate = "NULL"; 
    price = 0; 
} 

Sales::~Sales() {} 

物业头

#ifndef __PROPERTY_A_H__ 
#define __PROPERTY_A_H__ 


/*TODO REQUIRED HEADER FILES AND NAMESPACES*/ 
#include <string> 
#include "utility1.h" 


class Property 
{ 
protected: 
    string owner; 
    string address; 
    string suburb; 
    int postcode; 

public: 
    Property(); 
    Property(string theOwner, string theAddress, string theSuburb, int thepostCode); 
    virtual ~Property(); 

    string getOwner() const {return owner;}; //Note the use of const 
    string getAddress() const {return address;}; 
    string getSuburb() const {return suburb;}; 
    int getPostcode() const {return postcode;}; 

    void setOwner(string newOwner) {owner = newOwner;}; 
    void setAddress(string newAddress) {address = newAddress;}; 
    void setSuburb(string newSuburb) {suburb = newSuburb;}; 
    void setPostcode(int newPostcode) {postcode = newPostcode;}; 
}; 
#endif 

出租头

#ifndef __RENTALS_H__ 
#define __RENTALS_H__ 


#include "property_a.h" 

class Rentals : public Property 
{ 
protected: 
    double bond; 
    double monthlyRent; 

public: 
    Rentals(); 
    Rentals(string theOwner, string theAddress, string theSuburb, 
       int thepostCode, double theBond, double theMonthlyRent); 
    ~Rentals() ; 

    double getBond() const {return bond;}; //Note the use of const 

    void setBond(double theBond) {bond = theBond;}; 

    double getMonthlyRent() const {return monthlyRent;}; //Note the use of const 

    void setMonthlyRent(double theMonthlyRent) {monthlyRent = theMonthlyRent;}; 


}; 

#endif 

Answer 1

另一位评论者建议您查找object slicing.这并不说明问题，但是你可以通过添加一些调试语句，更具体地看到它您的代码：

std::cout << "Size of properties: " << sizeof(properties) << std::endl; 
std::cout << "Size of properties[4]: " << sizeof(properties[4]) <<std::endl; 
std::cout << "Size of tmpRent: "<< sizeof(tempRent) <<std::endl; 

输出看起来是这样的：

Size of properties: 440 
Size of properties[4]: 88 
Size of tmpRent: 104 

它看起来像一个属性元素是不是大到足以容纳你的子类的元素......这是怎么回事？

在声明Properties properties[5]，你正在声明类型属性的对象的数组，并将其分配的存储器的连续块。实际上，你可以看到，通过打印地址：

std::cout << "Start of properties: " << &properties <<std::endl; 
std::cout << "Address of properties[0]: " << &properties[0] << std::endl; 
std::cout << "Address of properties[1]: " << &properties[1] << std::endl; 
std::cout << "Address of properties[2]: " << &properties[2] << std::endl; 
std::cout << "Address of properties[3]: " << &properties[3] << std::endl; 
std::cout << "Address of properties[4]: " << &properties[4] << std::endl; 

在我的机器，我得到：

Start of properties: 0x7fff5a4c6070 
Address of properties[0]: 0x7fff5a4c6070 
Address of properties[1]: 0x7fff5a4c60c8 
Address of properties[2]: 0x7fff5a4c6120 
Address of properties[3]: 0x7fff5a4c6178 
Address of properties[4]: 0x7fff5a4c61d0 

这些都是很大的数字，但你可以看到，地址是由将0x58或88字节增加为数组中的每个元素。当你分配属性[4]时，C++将属性[4]作为指针处理，并将104字节复制到指向的位置。赋值属性[4] = tempRent相当于memcpy(&tempRent, &properties[4], 104)。 C++只是假设你有足够的内存来存放对象（这是104字节）。但是在内存块结束之前只剩下88个字节。您的分配将覆盖阵列的末尾并破坏下一段内存。该程序可能会崩溃在任何时候，它可能会显示损坏的数据，或者它可能看起来完全正常工作（因为它，当我在我的Mac上运行它。）