Access violation writing location error when i try to read from file

this is where i write to a file ->

void Supermarket_Billing_System::Add_and_WriteNewProduct(Product P)
{
    ofstream fl;
    fl.open("ProductList", ios::out | ios::binary);
    fl.write((char *) &P, sizeof(P));
    fl.close();
}

this is where i read from a file ->

void Supermarket_Billing_System::Read_DisplayProductFromProductList()
{
    Product P;
    int x;
    ifstream fp;
    fp.open("ProductList", ios::in);
    fp.seekg(0, ios::beg);
    fp.read((char *) &P, sizeof(P));
    x = P.GetProduct_qty();
    fp.close();
}

Product class looks like this ->

class Product
{
private:
     long int Product_no;
     std::string Product_name;
     double Product_price;
     int Product_qty;
     double Product_tax;
     double Product_dis;

public:

    //Constructor
    Product();
    Product(long int, string, double, int, double, double);

    //All Getters methods
    long int GetProduct_no();
    string GetProduct_name();
    double GetProduct_price();
    int GetProduct_qty();
    double GetProduct_tax();
    double GetProduct_dis();

    //All Setters methods
    void SetProduct_no(long int);
    void SetProduct_name(string);
    void SetProduct_price(double);
    void SetProduct_qty(int);
    void SetProduct_tax(double);
    void SetProduct_dis(double);

    void Accept_Product();
    void Accept_ProductForBilling();
    void Display_Product();
};

When i try to read from the file by calling Read_DisplayProductFromProductList() it gives me error ->

Unhandled exception at 0x6803ad54 (msvcp100d.dll) in Supermarket_Billing_System.exe: 0xC0000005: Access violation writing location 0xfeeefeee.

Your Product class is not trivially copyable due to the std::string member; you are not writing the actual string that Product_name holds in your write method, only the binary representation of a std::string, and the internal string pointer will almost certainly point to an invalid location when you read. Either way attempting to perform a bytewise copy of a non-trivially copyable class is undefined behavior.

You also haven't passed the binary flag when you open your file for reading

fp.open("ProductList", ios::in);

which will cause issues on Windows if there are any \r\n (0x0A 0x0D) sequences in the file you are reading.

You will either need to use a char array for your string, or manually handle the serialization of each member. The simplest way would be to use stream friend functions to write your object to a plain text file