CODEWITHSUNDEEP
c++oopsyntax
Zeshan Sajid
Zeshan Sajid

Reputation: 559

My C++ code gives error which is not seen in code. Whats the bug?

When I compile this code, it gives a runtime error shown below. But it doesn't tell which line is faulty in my code.

Debug Assertion Failed!

Program: C:\Windows\system32\MSVCP110D.dll
File: c:\program files (x86)\microsoft visual studio 11.0\vc\include\xstring
Line: 1143

Expression: invalid null pointer

For information on how your program can cause an assertion failure, see the Visual C++ documentation on asserts.

(Press Retry to debug the application.)

The following is my C++ code. Consisting one base class: Vehicle and another derived class: Car which is publicly inherited from the base class.

class Vehicle {

private:
    string VehicleNo, color;

public:
    Vehicle():VehicleNo(NULL),color(NULL){};
    string getVehicleNo(){return VehicleNo;}
    string getColor(){return color;}

    void setVehicleNo(){
        //getline(cin,VehicleNo);
        cin>>VehicleNo;
    }

    void setVehicleColor(){cin>>color;}
};



class Car: public Vehicle {

private:
    int distance;

public:
    void setDistance(int x){distance=x;}
    void setCarNo(){setVehicleNo();}
    void setCarColor(){setVehicleColor();}

    int calculateFare(int x){return 5*x;};


    void displayInformation()
    {
        cout<<"Your Car Number is: "<<getVehicleNo()<<endl;
        cout<<"The color of your Car is: "<<getColor()<<endl;
        cout<<"Total fare which you have to pay: "<<calculateFare(distance);

    }


};

int main()
{
    Car c1;
    int distance;
    char choice;

    cout<<"Enter car number: ";
    c1.setCarNo();

    cout<<"\nEnter Car Color: ";
    c1.setCarColor();

    cout<<"\nHow long would you like to go? Enter distance in kilometers: ";
    cin>>distance;
    c1.setDistance(distance);

    cout<<"\n----------------------------------\n";
    c1.displayInformation();
    cout<<"\n----------------------------------\n";

    cout<<"\nDo you want to calculate Fare of different distance (y/Y for yes and another character for No?  ";
    cin>>choice;

    do{

        cout<<"\nHow long would you like to go? Enter distance in Kilometers: ";
        cin>>distance;
        cout<<"\n----------------------------------\n";
        c1.setDistance(distance);

        c1.displayInformation();

        cout<<"\nDo you want to calculate Fare of different distance (y/Y for yes and another character for No?  ";
        cin>>choice;
    } 
    while(choice=='y' || choice=='Y');
}

Upvotes: 0

Views: 129

Answers (2)

Jonathan Mee
Jonathan Mee

Reputation: 38919

C++ provides 9 string constructors: http://en.cppreference.com/w/cpp/string/basic_string/basic_string

Of these 2 of them accept pointers:

  1. basic_string(const CharT* s, size_type count, const Allocator& alloc = Allocator())
  2. basic_string(const CharT* s, const Allocator& alloc = Allocator())

When you call VehicleNo(NULL) and color(NULL) you are only passing a null pointer and not a count to the string constructor so the compiler passes your null argument into option 2. Where s is expected to be:

A pointer to a character string to use as source to initialize the string with

When the string constructor attempts to dereference s to copy it's contents into the string being constructed it segfaults.

What you're trying to construct here is an empty string. C++ already does that when you use the default constructor: string().

A member object's default constructor will be called if no construction is specified in the constructor intialization list. So you won't need to put either VehicleNo or color in the constructor intialization list to construct them as empty strings. Meaning you can use the compiler's generated default constructor, and get rid of your constructor all together.

Upvotes: 4

Tarik Neaj
Tarik Neaj

Reputation: 548

Your problem is this line of code

Vehicle():VehicleNo(NULL),color(NULL){};

VehicleNO and color are of type string. They can't be NULL. Change it to something like this

Vehicle() :VehicleNo(" "), color(" "){};

Upvotes: -1

Related Questions