c++ - 读取结构化二进制文件 C++

Question

您好，我刚刚编写了以下程序，通过输入一些信息并在控制台中显示来创建一个 .dat 文件。但在用户提示中，程序在打印“显示记录”后崩溃，我确定读取函数(ItemFile.read(reinterpret_cast (&Item)，sizeof(Item))是错误的，但我被卡住了。感谢帮助。

 struct fileOperation
 {
      string ItemDescription;
      int QuantityAtHand;
      float WholeSaleCost;
      float RetailCost;
      int DateAddedtoInventory;

 };
 void DisplayFiles(fileOperation,fstream);
 fileOperation writtenFileInformation(fileOperation);

 fileOperation writtenFileInformation(fileOperation Item)
 {
    cout<<"Please enter inventory description "<<endl;
    cin>>Item.ItemDescription;
    cout<<"Please enter Quantity description "<<endl;
    cin>>Item.QuantityAtHand;
    cout<<"Please enter the whole sale cost "<<endl;
    cin>>Item.WholeSaleCost;
    cout<<"Please enter the retail sale cost"<<endl;
    cin>>Item.RetailCost;
    cout<<"DataAddedtoInventory "<<endl;
    cin>>Item.DateAddedtoInventory;
    return Item;
}

 int main()
 {
   fileOperation Item;
   fileOperation newObject;
   fileOperation Item1;
   int button;
   bool flag;
   flag=true;
   cout<<"This program perform following operations :"<<endl;
   cout<<"Add new records to the file .(press 1)"<<endl;
   cout<<"Displahy new records to the file .(press 2)"<<endl;
   cout<<"Change any Record to the file (press3)"<<endl;
   fstream ItemFile("inventory1.dat",ios::in|ios::out|ios::binary);
   cin>>button;
   if(button==1)
   {
     while(flag)
     {

        newObject=writtenFileInformation(Item);
        cout<<"you have :";
        ItemFile.write(reinterpret_cast<char *>(&Item),sizeof(Item));
        cout<<"Do you wish to continue"<<endl;
        cin>>button;
        if(button!=1)
        {
            flag=false;
        }
        ItemFile.close();
    }

}
else if(button==2)
{

    cout<<"DisplayRecords "<<endl;
    if(!ItemFile)
    {
        cout<<"Error opening file.program aborting.\n";
        return 0;
    }
    ItemFile.read(reinterpret_cast<char *>(&Item),sizeof(Item));
    while(!ItemFile.eof())
    {
        cout<<"Item description is: "<<Item.ItemDescription<<endl;
        cout<<"Quantity at hand is: "<<Item.QuantityAtHand<<endl;
        cout<<"Whole sale cost is: $"<<Item.WholeSaleCost<<endl;
        cout<<"Retail sale cost is: $"<<Item.RetailCost<<endl;
        cout<<"the data this have been added is "<<Item.DateAddedtoInventory<<endl;
        ItemFile.read(reinterpret_cast<char *>(&Item),sizeof(Item));
     }
    ItemFile.close();
}
}

Answer 1

ItemFile.write(reinterpret_cast<char *>(&Item),sizeof(Item));
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this is wrong

如果对象包含 std::string 对象，则不能逐字节直接持久化对象。它可能会维护一个内部指针，指向堆上动态分配的缓冲区(真正存储字符串数据的地方)，该指针在重新加载后可能会悬空。

你可以做的一件事是明确地获取数据(使用 c_str() 或 data() 成员函数)并将它们写入文件而不是 字符串对象。此外，请注意可移植性问题，例如 int 等多字节类型(可以选择 uint32_t 等固定宽度整数)，如果您的程序旨在在不同平台上运行。