对象未从文件中读取确切数据 [英] Object Not Read Exact Data From File

问题描述

我想从文件中读取数据，但是当我将其写入文件时，它成功地写入了文件，但是当我从文件中删除时，我给了我垃圾值.请Plz找到我无法检测到它无法读取的错误?
以下是我在vc ++中的代码

I want to read data from file but when i write it on file it wrote on file successfully but when i rem from file i give me garbage value. Plz find the Bug That i could n''t detect how it not read?
The following is my code in vc++

// reading_from_file.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include<iostream>
#include<conio.h>
#include<fstream>
using namespace std;
struct node
{
	int Id;
	node*next;
	node()
	{
		next=NULL;
	}
};
struct node1
{
	int id;
};
class LL
{
	node*first;

public:
	LL()
	{
		first=NULL;
	}
	void add(node*t)
	{
		if(first==NULL)
		{
			first=new node();
			first->Id=t->Id;
			first->next=NULL;
		}
		else
		{
			node*temp;
			temp=first;
			while(temp->next!=NULL)
				temp=temp->next;
			node*last=new  node();
			last->Id=t->Id;
			last->next=0;
			temp->next=last;
		}
	}
	void show()
	{
		node*tfirst=first;
		while(tfirst!=NULL)
		{
			cout<<"ID "<<tfirst->Id<<endl;
			tfirst=tfirst->next;
		}
	}
};
int _tmain(int argc, _TCHAR* argv[])
{
	node*insert=new node();
	LL obj;
	node1 ob;
	fstream fs;
	int i=1;
	fs.seekg(0);
	fs.open("Malik.txt",ios::in|ios::out|ios::binary|ios::app);
	while(!fs.eof())
	{
		fs.read(reinterpret_cast<char*>(&ob),sizeof(node1));
		cout<<"vALUE "<<(ob.id)<<endl;
		insert->Id=ob.id;
		obj.add(insert);
	}
	//while(i)
	//{
	//	//cout<<"Enter Key ";
	//	for(;i<=10;i++)
	//	{//cin>>insert->Id;	
	//		insert->Id=i*5;
	//		obj.add(insert);		
	//		fs.write(reinterpret_cast<char*>(&obj),sizeof(LL));
	//	}//cout<<"Press 0 To Terminate";
	//	//cin>>i;
	//}
	fs.close();
	//system("cls");
	obj.show();
	return 0;
}

推荐答案

没有看到您要写入文件的位置，我无法提出修复建议，但是我可以提出替代方案. 序列化 [ ^ ].这个想法是每个类/结构都负责保存/恢复自己的数据，这实际上简化了事情.

Without seeing where you are writing to the file, I can''t suggest a fix, however I can suggest an alternative. Serialization[^]. The idea is that each class/struct is responsible for saving/restoring its own data, which really simplifies things.

#include <stdio.h>

#include "stdafx.h"
#include<iostream>
#include<conio.h>
#include<fstream>

using namespace std;
 
struct node {
	node *next;
	int Id;
	/*This is an initialiser list, which is only valid in a constructor
	It has the same effect as "next = NULL; Id = id;", only it is a touch faster*/
	node(int id) : next(NULL), Id(id) { } //Add a parameter in here for the value to make construction neater when you make it
	void serialize(ostream &s) {
		//recursively write to file
		s.write((char *)&Id, sizeof(Id));
		if (next != NULL) {
			next->serialize(s);
		}
	}
	static node *unserialize(istream &s) {
		//recursively read from file
		int i;
		s.read((char *)&i, sizeof(i));
		if (s.eof()) {
			return NULL;
		}
		node *n = new node(i);
		n->next = unserialize(s);
		return n;
	}
};
 
class LL {
	node* first;
	//This allows us to add directly to the end of the list, instead of iterating through each element.
	//When you start getting a few hundred elements in the list you will notice the difference
	node* last;
 
public:
	LL() : first(NULL), last(NULL) { } //Another initialiser list
	~LL() {
		//Clean up the memory
		node *n = first;
		while (n != NULL) {
			node *del = n;
			n = n->next;
			delete del;
		}
	}

	void add(int i) {
		if(first == NULL) {
			first = new node(i);
			last = first;
		} else {
			//Isn't this easier?
			node *temp = new node(i);
			last->next = temp;
			last = temp;
		}
	}
	void show() {
		node *tfirst = first;
		while (tfirst != NULL) {
			cout<<"ID "<<tfirst->Id<<endl;
			tfirst = tfirst->next;
		}
	}
	void serialize(ostream &s) {
		if (first != NULL) {
			first->serialize(s);
		}
	}
	static LL *unserialize(istream &s) {
		LL *ll = new LL();
		ll->first = node::unserialize(s);
		ll->last = ll->first;
		return ll;
	}
};

int _tmain(int argc, _TCHAR* argv[]) {
	LL *ll = new LL();
	ll->add(1);
	ll->add(2);
	ll->add(4);
	ll->add(3);
	cout << "Original list:" << endl;
	ll->show();
	fstream fs;
	//NOTE: This opens the file for appending.
	//The original contents will remain in the file, and this will be added to the end
	fs.open("Malik.txt", ios::out|ios::binary|ios::app);
	ll->serialize(fs);
	delete ll;
	fs.close();
	fs.open("Malik.txt", ios::in|ios::binary|ios::app);
	cout << "Saved list:" << endl;
	ll = LL::unserialize(fs);
	ll->show();
	delete ll;
	fs.close();
	return 0;
}

另外，您可以使用模板 [

Also, you could use Templates[^] for this, which would make it a little more dynamic, if you need lists of multiple data types.

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