Question

所以我在这里打破了我的头脑。我一直在上下阅读，我只是无法弄清楚为什么我的程序崩溃，一旦我到达main中的for循环内的setLoan函数。 AM我错过了什么，或者我是否实现了错误的指针？提前致谢。

 #include <string>
#include <iostream>
using namespace std;

//Vehicle Class
class Vehicle {
public:
    Vehicle();
    void setPrice(double a);
    void setMpg(int a);
    double getPrice() const;
    int getMpg() const;
    void printVehicle() const;
    Vehicle(double price, int mpg);
private:
    double price;
    int mpg;
};

//Loan Class
class Loan {
public:
    void setBank(string a);
    void setLoan(double a);
    string getBank() const;
    double getLoan() const;
    void printLoan() const;
    Loan(string bank = "", double loan = 0);
private:
    string bank;
    double loan;
};

//Car Class
class Car : public Vehicle {
public:
    Car(double price = 0, int mpg = 0, string bank = "", double loan = 0, string name = "", int element = 0);
    void setName(string a);
    void setLoan(string b, double l, int element);
    string getName() const;
    void printFull() const;
    void setNbrOfLoans(int a);
    ~Car();
private:
    string name;
    Loan* pLoan;
    int nbrOfLoans;
};

//Main
int main() {
    Car car1(24800, 22, "Citi", 21600, "Mustang", 1);
    Car car2;
    Car* pCar1 = &car1;
    Car* pCar2 = &car2;
    cout << "Enter the price of the car: ";
    double price;
    cin >> price;
    pCar2->setPrice(price);
    cout << "Enter the mpg: ";
    int mpg;
    cin >> mpg;
    pCar2->setMpg(mpg);
    cout << "Enter the name of the car: ";
    string name;
    cin >> name;
    pCar2->setName(name);
    string bank;
    double loan;
    int index;
    cout << "Enter the amount of loans you obtained: ";
    cin >> index;
    pCar2->setNbrOfLoans(index);
    for (int i = 0; i < index; i++)
    {
        cout << "Enter the name of bank " << i + 1 << ": ";
        cin >> bank;
        cout << "Enter the amount of loan " << i + 1 << ": ";
        cin >> loan;
        pCar2->setLoan(bank, loan, i);
    }
    cout << endl;
    pCar1->printFull();
    pCar2->printFull();
    return 0;
}
////////////////////////////////////////////////////////////////////////////////////////
//Vehicle class function definitions
////////////////////////////////////////////////////////////////////////////////////////
Vehicle::Vehicle() {
    price = 0;
    mpg = 0;
}

Vehicle::Vehicle(double price, int mpg) {
    price = price;
    mpg = mpg;
}

void Vehicle::setPrice(double a) {
    price = a;
}

void Vehicle::setMpg(int a) {
    mpg = a;
}

double Vehicle::getPrice() const {
    return price;
}

int Vehicle::getMpg() const {
    return mpg;
}

void Vehicle::printVehicle() const {
    cout << "Price: " << price << endl;
    cout << "MPG: " << mpg << endl;
}

////////////////////////////////////////////////////////////////////////////////////////
//Loan Class function definitions
///////////////////////////////////////////////////////////////////////////////////////

Loan::Loan(string bank, double loan) {
    bank = bank;
    loan = loan;
}

void Loan::setBank(string a) {
    bank = a;
}

void Loan::setLoan(double a) {
    loan = a;
}

string Loan::getBank() const {
    return bank;
}

double Loan::getLoan() const {
    return loan;
}
void Loan::printLoan() const {
    cout << "Bank: " << bank << endl;
    cout << "Loan: " << loan << endl;
}

////////////////////////////////////////////////////////////////////////////////////
//Car Class function definitions
////////////////////////////////////////////////////////////////////////////////////
Car::Car(double price, int mpg, string bank, double loan, string name, int element) : Vehicle(price, mpg)
{
    nbrOfLoans = element;
    Car::name = name;
    pLoan = new Loan[nbrOfLoans];
}


void Car::setName(string a) {
    name = a;
}

void Car::setLoan(string b, double l, int element) {
    pLoan[element].setBank(b);
    cout << " ";
    pLoan[element].setLoan(l);
}

string Car::getName() const {
    return name;
}

void Car::setNbrOfLoans(int a) {
    nbrOfLoans = a;
}

void Car::printFull() const {
    cout << endl << "Name: " << name << endl;
    printVehicle();
    for (int i = 0; i < nbrOfLoans; i++)
    {
        cout << pLoan[i].getBank();
        cout << endl;
        cout << pLoan[i].getLoan();
        cout << endl;
    }
}

Car::~Car() {
    delete[] pLoan;
}

Answer 1

当您为Car::setLoan致电pCar2时，您正在尝试访问大小为零的动态数组。

Car car2;//the nbrOfLoans member is 0 and pLoan is not pointing to anywhere
....
Car* pCar2 = &car2;//the nbrOfLoans member is 0 and pLoan is not pointing to anywhere
...
Car::Car(double price, int mpg, string bank, double loan, string name,    int element) : Vehicle(price, mpg)
{
   ...
   pLoan = new Loan[nbrOfLoans];//doesn't create anything if nbrOfLoans is 0, which is the default
}

当你第一次尝试在第二辆汽车（car2）的构造函数中为pLoan分配内存时，nbrOfLoans的大小为0，所以你的指针没有指向任何东西。之后您尝试通过调用pCar2->setLoan(bank, loan, i);来访问它。

如果您可以使用std::vector会更好，否则您需要在知道它应该保持的大小后创建/调整动态数组的大小，即在获得nbrOfLoans的值Car::setNbrOfLoans之后1}}。

void Car::setNbrOfLoans(int a) {
   nbrOfLoans = a;

   if(pLoan!=NULL)
     delete[] pLoan;

   pLoan = new Loan[nbrOfLoans];
}

有人能够发现我使用这个c ++代码做错了什么吗？

1 个答案: