c++ - 从 C++ 中的类指针对象调用方法(字符串)

Question

以下代码会产生一个运行时错误，其中类的调用方法不会产生任何结果。

MAIN.cpp :

#include "carClass.h"
#include <fstream>
#include <iostream>
#include <string>
#include <iostream>
#include <iomanip>

using namespace std;

string VIN;
int miles;
string dealer;
int price;

int main(int argc, char** argv) {

    char command;
    ifstream infile;
    ofstream outfile;

    //Checks if the data file exists

    infile.open("base.txt", ifstream::in);
    outfile.open("base.txt", ios_base::app);

    cout << "Enter a command:" << endl;
    cin >> command;
    while (command != 'q') 
    {
        switch (command) 
        {       
            case 'a':
            {
                cin >> command;
                if (command == 'c') 
                {
                 //Gets user input
                    cin >> VIN >> miles >> dealer >> price;

                 //Creates new pointer variable with the user data
                    Car* vehicule = new Car(VIN, miles, dealer, price);
                    VIN=vehicule->getVin();                     
                    cout << "vehicule object VIN is: " << VIN;
                    //end of for loop
                }//end of if loop            
            }//end of case loop
            break;
        }//end of switch
        cout << "Enter a command:" << endl;
        cin >> command;
    }//end of while loop
    outfile.close();
    infile.close();
    return 0;
}

Here is where I try to call the method to my object pointer VIN=(*vehicule).getVin();

I also tried vehicule->getVin(); and it did not work

---

Here is where I check if anything was stored and returns blank cout << "vehicule object VIN is: " << VIN;

如果您想在这里看到源文件和头文件

carClass.cpp :

#include "carClass.h"
#include <string>
#include <iostream>
#include <fstream>
using namespace std;

Car::Car()
{
    string VIN; 
    int mileage=0; 
    string dealership; 
    int price=0;
    string vinCode;
}

Car::Car(string vin, int miles,string carDealer, int dollars)
{
    string VIN=vin; 
    int mileage=miles; 
    string dealership=carDealer; 
    int price=dollars;
    string vinCode = VIN.substr(0,3); 

}

void Car::addToBase(ofstream& file)
{
    file << "c" << endl << VIN << endl << this->mileage << endl <<
            this->dealership << endl << this->price << endl; 
    return;
}

carClass.h :

#ifndef CAR_H
#define CAR_H
#include <string>
#include <iostream>
#include <fstream>
using namespace std;

class Car {
    public:
        Car();
        Car(string, int, string, int);
        void addToBase(ofstream&);
        string getVin(){return VIN;}
        int getMiles(){return mileage;}
        string getDealer(){return dealership;}
        int getPrice(){return price;}
        string getVinCode(){return vinCode;}

    private:
        string VIN;
        int mileage;
        string dealership;
        int price;
        string vinCode;
};  
#endif

Answer 1

正在从 stdin 正确读取变量。问题在于您的构造函数:

Car::Car()
{
    string VIN; // local variable (this and all the other variables)!
    int mileage=0; 
    string dealership; 
    int price=0;
    string vinCode;
}

Car::Car(string vin, int miles,string carDealer, int dollars)
{
    string VIN=vin;  // local variable (this and all the other variables)! 
    int mileage=miles; 
    string dealership=carDealer; 
    int price=dollars;
    string vinCode = VIN.substr(0,3); 

}

在它们中你都使用了一个局部变量(即它的作用域是构造函数的作用域)。您应该改用成员变量，如下所示:

Car::Car()
{
    // Default constructor, no need to initialize VIN (though you may want to initialize it to some default value of course) 
    mileage=0; 
    price=0;
}

Car::Car(string vin, int miles,string carDealer, int dollars)
{
    VIN=vin; // VIN is a member variable 
    mileage=miles; 
    dealership=carDealer; 
    price=dollars;
    vinCode = VIN.substr(0,3); 
}