c++ - 在 C++ 中使用动态内存使程序崩溃

Question

我的程序在标准内存分配下运行良好，但使用动态内存分配会使程序运行异常!它甚至不从主要功能打印任何东西。

在头文件中声明指向alist 的指针，并在类定义(构造函数)中使用new 动态分配内存。已指出女巫程序的代码工作正常。也用了很多couts做测试，无视。谢谢

头文件:

//Vehicle.h
//Author: Ankush Kaul
//Purpose: Declaration of Vehicle class

#ifndef VEHICLE_H
#define VEHICLE_H

#include <string>
#include <fstream>

using namespace std;


class Vehicle
{
public:
    Vehicle(); //default constructor
    Vehicle(ifstream&); //parametrized constructor
    Vehicle(const Vehicle& other); //copy constructor
    ~Vehicle(); // destructor

    //over loaded operators
    Vehicle& operator=(const Vehicle& other); // assignment operator
    bool operator==(const Vehicle& other); // relational operator

    // accessors
    int getVid();
    string getManufact();
    string getColor();
    double getCost();
    int getnumAccessories();
    string getList();

    // 3 functions to access accessory list
    void startAcc();
    string nextAcc();
    bool hasNextAcc();

protected:

private:
    int vId;
    string manufact;
    string color;
    double cost;
    int numAccessories;
    string *alist; // acessory list 
    //string alist[10]; <- WORKS WITH THIS
    int counter; // hidden object used for accessing accesory list
};

#endif // VEHICLE_H

类定义:

//Vehicle.h
//Author: Ankush Kaul
//Purpose: Implementation of Vehicle class

#include "Vehicle.h"
#include <cstdlib>
#include <fstream>
#include <iostream>

using std::atoi;
using std::atof;
using std::ifstream;
using std::cout;


//---------------------------
//Name: Vehicle
//Purpose: default constructor
//Parameters: None
//Return: None
//---------------------------
Vehicle::Vehicle()
{
    vId = 999;
    manufact = color = "";
    cost = numAccessories = 0;
}

//---------------------------
//Name: Vehicle()
//Purpose: Parametrized constructor
//Parameters:
//      fin : input file stream
//Return: None
//---------------------------
Vehicle::Vehicle(ifstream &fin)
{
    string line;

    getline(fin, line);
    vId = atoi(line.c_str());

    getline(fin, line);
    manufact= line;

    getline(fin, line);
    color = line;

    getline(fin, line);
    cost = atof(line.c_str());

    getline(fin, line);
    numAccessories = atoi(line.c_str());

    alist = new string[numAccessories]; <-- WORKS WITHOUT THIS
    cout<<"**";

    for (int i = 0; i < numAccessories; i++)
    {
        getline(fin, line);
        alist[i] = line;
    }

}

//---------------------------
//Name: ~Vehicle
//Purpose: Destructor
//Parameters: None
//Return: None
//---------------------------
Vehicle::~Vehicle()
{
}

//---------------------------
//Name: Vehicle()
//Purpose: Copy constructor
//Parameters:
//      other : Vehicle object passed to copy
//Return: None
//---------------------------
Vehicle::Vehicle(const Vehicle& other)
{
    this->vId = other.vId;
    this->manufact = other.manufact;
    this->color = other.color;
    this->cost = other.cost;
    this->numAccessories = other.numAccessories;

    for ( int i = 0 ; i < other.numAccessories ; i++ )
        this->alist[i] = other.alist[i];
}

//---------------------------
//Name: operator=
//Purpose: Overloading operator
//Parameters:
//      other : Vehicle object passed to assign values
//Return: Vehicle
//---------------------------
Vehicle& Vehicle::operator=(const Vehicle& other)
{
    this->vId = other.vId;
    this->manufact = other.manufact;
    this->color = other.color;
    this->cost = other.cost;
    this-> numAccessories = other.numAccessories;

    for ( int i = 0 ; i < other.numAccessories ; i++ )
        this->alist[i] = other.alist[i];

    return *this;
}

//---------------------------
//Name: operator==
//Purpose: Overloading operator
//Parameters:
//      other : Vehicle object passed to compare
//Return: bool
//---------------------------
bool Vehicle::operator==(const Vehicle& other)
{
    if (this->vId == other.vId &&
         this->manufact == other.manufact &&
          this->color == other.color &&
           this->cost == other.cost &&
            this->numAccessories == other.numAccessories)
    {
        return true;
    }

    return false;
}

//---------------------------
//Name: getVid
//Purpose: gets vId attribute
//Parameters: none
//Return: int
//---------------------------
int Vehicle::getVid()
{
    return vId;
}

//---------------------------
//Name: getManufact
//Purpose: gets manufact attribute
//Parameters: none
//Return: string
//---------------------------
string Vehicle::getManufact()
{
    return manufact;
}

//---------------------------
//Name: getColor
//Purpose: gets color attribute
//Parameters: none
//Return: string
//---------------------------
string Vehicle::getColor()
{
    return color;
}

//---------------------------
//Name: getCost
//Purpose: gets cost attribute
//Parameters: none
//Return: double
//---------------------------
double Vehicle::getCost()
{
    return cost;
}

//---------------------------
//Name: getnumAccessories
//Purpose: gets numAccessories attribute
//Parameters: none
//Return: int
//---------------------------
int Vehicle::getnumAccessories()
{
    return numAccessories;
}

// 3 functions to get accesory list

//---------------------------
//Name: startAcc
//Purpose: sets counter to zero
//Parameters: none
//Return: void
//---------------------------
void Vehicle::startAcc()
{
    counter = 0;
}

//---------------------------
//Name: nextAcc
//Purpose: returns name of accesory
//Parameters: none
//Return: string
//---------------------------
string Vehicle::nextAcc()
{
    return alist[counter++];
}

//---------------------------
//Name: hasNextAcc
//Purpose: checks if all accessory list is read
//Parameters: none
//Return: bool
//--------------------------
bool Vehicle::hasNextAcc()
{
    if ( counter < numAccessories)
        return true;

    return false;
}

主文件:

//main.cpp
//Topic: Project 4 - Vehicle
//Author: Ankush Kaul
//Purpose: Read and display list of Vehicles

#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
#include <iomanip>
#include "Vehicle.h"

using namespace std;

void printVehicle (Vehicle);

int main ()
{

    ifstream fin; // holds input file stream
    string file,line; // file - holds filename, line - holds line read from file

    cout<<"Enter filename : ";
    cout<<"()";
    //cin>>file;
    cout<<"11";
    //fin.open(file.c_str());
    fin.open("vehicle1.txt");
    cout<<"^^";
    // checking if file is sucessfully opened
    if (!fin.is_open())
    {
        cout<<"Error opening file!";
        return 1;
    }
    cout<<"@@";

    //cin.ignore(1000, '\n');
    cout<<"%%";
    getline(fin, line); // reading the first line which contains number of vehicles in the file
    cout<<"!!";
    int count = atoi(line.c_str());
    cout<<"&&";
    Vehicle veh[count]; // defining a array of length = count

    // loop to read details of vehicles from file and store it in the veh[] array
    for (int i = 0; i < count; i++)
    {
        cout<<"##";
        Vehicle newVeh(fin);

        bool duplicate = false; // sets duplicate flag to false

        // loop to check if a duplicate vehicle exists
        for (int k = 0; k < i; k++)
            if (newVeh == veh[k])
            {
                duplicate = true;
                cout<<endl<<"Duplicate Vehicle detected --- ignored!"<<endl;
            }

        if (duplicate)
            continue;

        veh[i] = newVeh;
    }

    // print list of vehicles to the screen by calling printVehicle function
    cout<<endl<<"Vehicle List";

    for (int i = 0; i < count; i++)
    {
    //cout<<endl<<"in loop "<<i<<endl;
    cout<<endl<<"-------------------------";
    printVehicle(veh[i]);
    }

    return 0;
}

//---------------------------
//Name: printVehicle
//Purpose: prints the vehicle details
//Parameters: veh
//Return: void
//---------------------------
void printVehicle(Vehicle veh)
{
    cout<<endl<<"Vin: "<<veh.getVid();
    cout<<endl<<"Manufacturer: "<<veh.getManufact();
    cout<<endl<<"Color: "<<veh.getColor();
    cout<<fixed<<showpoint<<setprecision(2); // output modifier to print decimal with 2 point accuracy
    cout<<endl<<"Cost: "<<veh.getCost();
    cout<<endl<<"Accessory List:"<<endl;

    // printing accessory list
    veh.startAcc();
    while(veh.hasNextAcc())
    {
        string nextAcc = veh.nextAcc();
        cout<<"  "<<nextAcc<<endl;
    }

}

Answer 1

您的复制构造函数和赋值运算符已损坏。您没有为附件列表分配内存。您的复制构造函数应如下所示:

Vehicle::Vehicle(const Vehicle& other)
:
    vId (other.vId),
    manufact (other.manufact),
    color (other.color),
    cost (other.cost),
    numAccessories (other.numAccessories),
    alist (0),
    counter (0)
{
    alist = new string[numAccessories]; 
    for ( int i = 0 ; i < other.numAccessories ; ++i ) {
        alist[i] = other.alist[i];
    }
}

你的赋值运算符应该在分配给它之前类似地分配 alist 。您没有解决的赋值运算符还有另一个问题，即自赋值问题。如果有人执行 vehicle = vehicle; 怎么办？

您的析构函数也不正确。您应该释放由构造函数或赋值运算符分配的内存。

您的比较运算符没有损坏，但它也可能不正确。据推测，您应该测试两辆车是否具有相同的配件，而不是仅仅测试它们是否具有相同数量的配件。