Question

我在堆上有内存问题。看我正在尝试做多态，所以我分配了我正在使用的类的多态层次结构的基类的指针数组。但是，我遇到的问题是，当我将堆上的内存分配给指针数组中的指针时，此内存将在稍后的程序中删除。保存对动态分配的内存的引用的指针不会超出范围，但由于某种原因，我指针指向的数据变得无法访问/删除

#include "OverNightPackage.h"
#include "TwoDayPackage.h"
#include <iostream>
#include <string>


using namespace std;

int main()
{
const double overnightextracost = 1.45;
const double flatfee2day = 3.00;
const double costperoz = 1.55;
Package* packagelist[5] = {NULL};
int numpackages = 0;
bool sendanother = true;

string name;
string address;
string city;
string state;
string zip;
double weight;
cout << " Welcome to the package shipper\n\n";
cout << " You will now enter your information\n";
cout << " Please enter your name ";
getline(cin, name);
cout << "\n Please enter your address (ex 5228) \n";
getline(cin, address);
cout << "\n Please enter your city \n";
getline(cin, city);
cout << "\n Please enter your state\n";
getline(cin, state);
cout << "\n Please enter your 5 digit zipcode\n";
getline(cin, zip);

Destination sender(name, address, city, state, zip);

while(sendanother && numpackages < 10)
{
    sendanother = false;
    numpackages++;
    cout << "\n\n You will now enter the package recievers information\n";
    cout << " Please enter recievers name ";
    getline(cin, name);
    cout << "\n Please enter recievers address (ex 5228) \n";
    getline(cin, address);
    cout << "\n Please enter recievers city \n";
    getline(cin, city);
    cout << "\n Please enter recievers state\n";
    getline(cin, state);
    cout << "\n Please enter recievers 5 digit zipcode\n";
    getline(cin, zip);

    Destination receiver(name, address, city, state, zip);

    cout << "\n\n Please enter the weight of your package \n";
    cin >> weight;
    cin.ignore();

    char menuchoice;
    cout << "\n\n\n How would you like to ship your package?\n";
    cout << " Your options are\n 1.) Regular Shipping -- " << costperoz << " cost per ounce\n";
    cout << " 2.) 2 Day Delivery -- " << flatfee2day << " flatfee added\n";
    cout << " 3.) OverNight Delivery -- " << overnightextracost << " added per ounce\n";
    cin >> menuchoice;

    if(menuchoice == '1')
    {
        //static Package * package = new Package(sender, receiver, weight, costperoz);
        packagelist[numpackages] = new Package(sender, receiver, weight, costperoz);
    }
    if(menuchoice == '2')
    {
        //TwoDayPackage * package = new TwoDayPackage(sender, receiver, weight, costperoz, flatfee2day);
        packagelist[numpackages] = new TwoDayPackage(sender, receiver, weight, costperoz, flatfee2day);
    }
    if(menuchoice == '3')
    {
        //static OverNightPackage * package = new OverNightPackage(sender, receiver, weight, costperoz, overnightextracost);
        packagelist[numpackages] = new OverNightPackage(sender, receiver, weight, costperoz, overnightextracost);
    }

    cin.ignore();
    cout << "\n\n Would you like to add another package? Y or N\n\n";
    cin >> menuchoice;

    if(menuchoice == 'Y' || menuchoice == 'y')
            sendanother = true;
    else
        sendanother = false;

    cin.ignore();



}
    cout << " \n\n\n --- Shipment Information Below ---\n\n";

    for(int i = 0; i < numpackages; i++)
    {
        if(packagelist[i] != NULL)
        {
            packagelist[i]->print();
            cout << "\n Shipment Price -- $" << packagelist[i]->calcCost() << "\n\n";
        }

    }




for(int i = 0; i < numpackages; i++)
    delete packagelist[i];

system("pause");
return 0;
}

当我到达结束部分的时候，我循环遍历数组并尝试使用polhymorphic函数，这就是我开始获取内存访问冲突错误的地方（当我排除if（paackagelist [i]！= NULL）时。因此，由于某种原因，我在堆上分配给指针数组的数据超出了范围

Answer 1

与'范围'无关（在这种情况下，不能确定你的意思）。

问题出在numpackages++的位置。在将数据包添加到数组之前递增它，之后应该增加它。

边界检查也是错误的。您的packagelist数组的大小为5，但您在while循环中显示numpackages < 10。这两个值应该是相同的，最好你应该声明一个常量，以确保它们是相同的。

（C ++）堆上的内存变得可访问/被删除

1 个答案: