错误C4308：负整数常量转换为无符号类型C加上，我该如何解决这个问题？

Question

我正在尝试访问这里的二进制文件，我有一个名为teacher.dat的文件，它是一个二进制文件。我该如何解决这个问题？

fstream fp;
    Teacher obj;
    int found = 0;
    fp.open("teacher.dat", ios::in | ios::out);
    while (fp.read((char*)&obj, sizeof(obj)) && found == 0)
    {
        if (obj.GetEmail() == email)
        {

            obj.display();
            string password;
            cout << "\nEnter The New password : ";
            cin >> password;
            obj.SetPassword(password);
//Error is indicated here
        int pos = (-1)*sizeof(obj);
            fp.seekp(pos, ios::cur);
            fp.write((char*)&obj, sizeof(obj));
            found = 1;
        }
        else{
            cout << "\a Invalid email !" << endl;
        }
    }

Answer 1

删除

else
{
     cout << "\a Invalid email !" << endl;
}

并写

if (!found)
{
     cout << "\a Invalid email !" << endl;
}

out of while（）循环。

int pos = -1 * (signed)sizeof(obj);