从二进制文件C++更新数据

我正在编写一个简单的程序，它可以对数据进行删除，修改和其他操作。

不幸的是，我在修改二进制文件中的数据时陷入困境。

这是下面的更新记录函数的代码。

当我尝试指向前一个记录时，VS2017会给我下一个错误：

"more then one operator '-' matches these operands"...

请帮忙，

谢谢！！！

#include <iostream>
#include <fstream>
#include <cstring>
#include <stdio.h>
using namespace std;
class Book
{
private:
int bookid;
char title[50];
float price;
public:
Book()
{
bookid = 0;
strcpy(title, "no title");
price = 0;
}
void getDate()
{
cout << "Enter book id, title and price.";
cin >> bookid;
cin.ignore();
cin.getline(title, 49);
cin >> price;
}
void showData()
{
cout << bookid << "  " << title << "  " << price << endl;
}
int storeDate();
void viewAllBooks();
void searchBook(char *);
void deleteBook(char *);
void updateBook(char *);
};
void Book::updateBook(char *t)
{
int pos;
fstream file;
file.open("file.dat", ios::ate | ios::in | ios::out | ios::binary);
file.seekg(0); // read data from the begining of file
file.read((char *)this, sizeof(*this));
while (!file.eof()) // it return 1 so i use not operator to break while loop
{
if (!strcmp(title, t))
{
getDate();
file.seekp(file.tellg() - sizeof(this));
file.write((char *)this, sizeof(*this));
}
file.read((char *)this, sizeof(*this));
}
file.close();
}
void Book::deleteBook(char *t)
{
ifstream fin;
ofstream fout;
fin.open("file.dat", ios::in | ios::binary);
if (!fin.is_open())
{
cout << "File not found" << endl;
}
else
{
fout.open("temp.dat", ios::out | ios::binary);
fin.read((char*)this, sizeof(*this)); // 
while (!fin.eof())
{
if (strcmp(title, t))
{
fout.write((char *)this, sizeof(*this));
}
fin.read((char *)this, sizeof(*this));
}
fin.close();
fout.close();
remove("file.dat");
rename("temp.dat", "file.dat");
}
}
int Book::storeDate()
{
if (bookid == 0 && price == 0)
{
cout << "Book data in not initialized." << endl;
return (0);
}
else
{
// write data on file
ofstream fout;
fout.open("file.dat", ios::app | ios::binary);
fout.write((char*)this, sizeof(*this));
fout.close();
return (1);
}
}
void Book::searchBook(char *t)
{
int count = 0;
ifstream fin;
fin.open("file.dat", ios::in | ios::binary);
if (!fin.is_open())
{
cout << "File not found" << endl;
}
else
{
fin.read((char*)this, sizeof(*this));
while (!fin.eof())
{
if (!strcmp(t, title))
{
showData();
count++;
}
fin.read((char*)this, sizeof(*this));
}
if (count == 0)
{
cout << "No record Found." << endl;
}
fin.close();
}
}
void Book::viewAllBooks()
{
ifstream fin;
fin.open("file.dat", ios::in | ios::binary);
if (!fin.is_open())
{
cout << "File not found" << endl;
}
else
{
// type casting is using here as char
fin.read((char*)this, sizeof(*this));
while (!fin.eof())
{
showData();
fin.read((char*)this, sizeof(*this));
}
fin.close();
}
}
int main()
{
int choice;
char t[50];
Book b1;
cout << "1- Add Book" << endl;
cout << "2- View all Books" << endl;
cout << "3- Find a Book" << endl;
cout << "4- Delete a Book" << endl;
cout << "5- Update Book" << endl;
cout << "Enter choice: ";
cin >> choice;
switch (choice)
{
case 1:
b1.getDate();
b1.storeDate();
break;
case 2:
b1.viewAllBooks();
break;
case 3:
cout << "Enter Book title: ";
cin.ignore();
cin.getline(t, 49);
b1.searchBook(t);
break;
case 4:
cout << "Enter Book title: ";
cin.ignore();
cin.getline(t, 49);
b1.deleteBook(t);
break;
case 5:
cout << "Enter Book title: ";
cin.ignore();
cin.getline(t, 49);
b1.updateBook(t);
break;
default:
cout << "You entered invalid choice." << endl;
break;
}
system("PAUSE");
}