【发布时间】：2014-12-05 03:52:55
【问题描述】：
我正在编写一个对我的编程课非常重要的程序，但有些东西我不太明白；当我尝试从打开程序后创建的二进制文件中读取时，即使文件在目录中，它也会失败，并且在我尝试擦除文件的内容后，我仍然可以从文件中“读取”它们即使当我在资源管理器中检查时所说的文件是空的。我由此确定，即使我使用的是 BinaryFile.read，它也不是真正从文件中读取，而是从程序本身中存储的变量中读取。如何让我的程序从实际文件中读取？
（请注意，这还不是一个完整的程序，因此注释部分和空函数。）
（另外请注意，由于我班级的性质，我只能使用已经教过的内容（即 fstream 标头中的任何内容以及之前制作基本程序所必需的大多数内容 - 他是让我也使用 stdio.h 中的东西。）
//
// main.cpp
// Binary Program
//
// Created by Henry Fowler on 11/19/14.
// Copyright (c) 2014 Bergen Community College. All rights reserved.
#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>
#include <cstdlib>
#include <math.h>
#include <stdio.h>
using namespace std;
struct Record
{
char Name[20];
char LastName[20];
double Pay;
int Clearance;
int ID;
};
void CreateFile(fstream&); //Working
void CheckExist(fstream&); //Working
void Populate(fstream&,Record[],int&,int&); //Working
void Display(fstream&,Record[],int&,int&); //Working
void Append(fstream&,Record[],int&,int&); //Working
void DeleteFromFile(fstream&,fstream&,Record[],int&,int&);
// void SearchInFile(fstream&,Record[],int&,int&);
// void ModifyRecord(fstream&,Record[],int&,int&);
//void SortFile();
void WipeFile(fstream&);
void DelFile(fstream&);
int main(int argc, const char * argv[])
{
Record EmpRecords[20];
char Binary[] = "BinaryFile.dat";
char Binary2[] = "BinaryFileTemp.dat";
int maxsize; //make sure to set i to max size so you can use it later for things like wiping the file or deleting specific records
fstream BinaryFile;
fstream BinaryFile2;
string InputStr;
// char Read;
//int Choice = 0;
int i = 0;
int choice = 0;
int switchchoice;
CreateFile(BinaryFile); //working
CheckExist(BinaryFile); //working
BinaryFile.close();
while(choice==0)
{
cout << "Options: " << endl;
cout << "End Program (0)" << endl;
cout << "Input new records to file (1)" << endl;
cout << "Display current contents of file (2)" << endl;
cout << "Append a record at the end of the file (3)" << endl;
cout << "Delete a record from the file (4)" << endl;
cout << "Search for a record in the file (5)" << endl;
cout << "Modify a certain record (6)" << endl;
cout << "Sort file (unimplemented)" << endl;
cout << "Wipe contents of file (8)" << endl;
cout << "Please choose an option: ";
cin >> switchchoice;
switch(switchchoice)
{
case 0:
{
cout << "Exiting.";
BinaryFile.close();
system("PAUSE");
return 0;
break;
}
case 1:
{
Populate(BinaryFile, EmpRecords,i,maxsize); //working
break;
}
case 2:
{
Display(BinaryFile, EmpRecords,i,maxsize); //working i think
break;
}
case 3:
{
Append(BinaryFile, EmpRecords,i,maxsize); //working
break;
}
case 4:
{
DeleteFromFile(BinaryFile,BinaryFile2,EmpRecords,i,maxsize); //!
break;
}
case 5:
{
// SearchInFile(BinaryFile, EmpRecords,i,maxsize); //!
break;
}
case 6:
{
// ModifyRecord(BinaryFile, EmpRecords,i,maxsize); //!
break;
}
case 7:
{
cout << "Error, file sorting is currently unimplemented. Please try again.";
break;
}
case 8:
{
WipeFile(BinaryFile);
break;
}
}
}
system("PAUSE");
return 0;
}
void CreateFile(fstream& BinaryFile)
{
BinaryFile.open("BinaryFile.dat", ios::out | ios::binary);
}
void CheckExist(fstream &BinaryFile)
{
if(BinaryFile.good())
{
cout << endl << "File does exist" << endl;
}
else
{
cout << "file named can not be found \n";
system("PAUSE");
}
}
void Populate(fstream &BinaryFile,Record EmpRecords[],int &i, int &maxsize)
{
BinaryFile.open("BinaryFile.dat", ios::out | ios::binary);
int choice = 0;
while(choice==0)
{
cout << "Please input employee first name: ";
cin >> EmpRecords[i].Name;
cout << "Please input employee last name: ";
cin >> EmpRecords[i].LastName;
cout << "Please input Employee Pay: ";
cin >> EmpRecords[i].Pay;
cout << "Please input Employee Clearance (1-10): ";
cin >> EmpRecords[i].Clearance;
cout << "Please input Employee ID (6 numbers, i.e. 122934): ";
cin >> EmpRecords[i].ID;
cout << "Input another employee's information? (0) = yes, (1) = no: ";
cin >> choice;
BinaryFile.write((char *) (&EmpRecords[i]),sizeof(EmpRecords[i]));
i = i+1;
}
maxsize = i;
cout << "i is " << i << endl;
cout << "maxsize is " << maxsize << endl;
BinaryFile.close();
}
void Display(fstream &BinaryFile,Record EmpRecords[],int &i,int &maxsize)
{
BinaryFile.open("BinaryFile.dat", ios::in | ios::binary | ios::app);
int i2 = maxsize;
i = 0;
while(i2>0)
{
BinaryFile.read((char *) (&EmpRecords[i]),sizeof(EmpRecords[i]));
cout << i << endl;
cout << EmpRecords[i].Name << " " << EmpRecords[i].LastName << endl;
cout << "Pay: $" << EmpRecords[i].Pay << endl;
cout << "Clearance: " << EmpRecords[i].Clearance << endl;
cout << "Employee ID: " << EmpRecords[i].ID << endl;
BinaryFile.read((char *) (&EmpRecords[i]),sizeof(EmpRecords[i]));
cout << endl;
i2 = i2-1;
i = i+1;
}
BinaryFile.close();
}
void Append(fstream &BinaryFile,Record EmpRecords[],int &i,int &maxsize)
{
BinaryFile.open("BinaryFile.dat", ios::out|ios::binary|ios::ate|ios::app);
cout << "Please input employee first name: ";
cin >> EmpRecords[maxsize].Name;
cout << "Please input employee last name: ";
cin >> EmpRecords[maxsize].LastName;
cout << "Please input Employee Pay: ";
cin >> EmpRecords[maxsize].Pay;
cout << "Please input Employee Clearance (1-10): ";
cin >> EmpRecords[maxsize].Clearance;
cout << "Please input Employee ID (6 numbers, i.e. 122934): ";
cin >> EmpRecords[maxsize].ID;
cout << "Input another employee's information? (0) = yes, (1) = no: ";
BinaryFile.write((char *) (&EmpRecords[i]),sizeof(EmpRecords[i]));
maxsize = maxsize+1;
cout << "maxsize is " << maxsize << endl;
BinaryFile.close();
}
void DeleteFromFile(fstream &BinaryFile,fstream &BinaryFile2, Record EmpRecords[],int &i,int &maxsize)
{
BinaryFile.open("BinaryFile.dat", ios::out|ios::binary|ios::app);
BinaryFile2.open("BinaryFileTemp.dat", ios::out|ios::binary|ios::app);
int Choice;
cout << "Would you like to delete a file by name or by employee number?" << endl;
cout << "Name (1)" << endl;
cout << "Number (2)" << endl;
cout << "Choice: ";
cin >> Choice;
int i2 = maxsize;
if(Choice==1)
{
cout << "Please input employee first name: ";
// cin >> firstname;
cout << "Please input employee last name: ";
// cin >> lastname;
cout << "Searching...";
int i2 = maxsize;
i = 0;
while(i2>0)
{
BinaryFile.read((char *) (&EmpRecords[i]),sizeof(EmpRecords[i]));
cout << i << endl;
BinaryFile.read((char *) (&EmpRecords[i]),sizeof(EmpRecords[i]));
// if(EmpRecords[i].Name == firstname)
// {
// cout << "Found first name." << endl;
// if (EmpRecords[i].LastName == lastname)
// {
// cout << "Found last name." << endl;
/// }
// }
// else
// {
// cout << "Could not find name.";
// // BinaryFile2.write((char *) (&EmpRecords[i]),sizeof(EmpRecords[i]));
// }
cout << endl;
i2 = i2-1;
i = i+1;
}
}
BinaryFile.close();
if( remove( "BinaryFile.dat" ) != 0 )
cout << endl << "Error deleting file" << endl;
else
{
cout << "File successfully deleted" << endl << endl;
}
int result;
char oldname[]="BinaryFileTemp.dat";
char newname[]="BinaryFile.dat";
result = rename(oldname,newname);
if(result == 0)
cout << "DEBUG: Success" << endl;
else
cout << "DEBUG: Failure" << endl;
}
void WipeFile(fstream &BinaryFile)
{
int sure;
cout << "There is no undoing this action." << endl;
cout << "Continue (1)" << endl;
cout << "Cancel (2)" << endl;
cout << "Wipe file? ";
cin >> sure;
if(sure == 1)
{
cout << "Wiping file.";
BinaryFile.open("BinaryFile.dat", ios::out | ios::binary | ios::trunc);
BinaryFile.close();
}
else
{
cout << "Canceling.";
}
}
void DelFile(fstream &BinaryFile)
{
BinaryFile.close();
if( remove( "BinaryFile.dat" ) != 0 )
cout << endl << "Error deleting file" << endl;
else
{
cout << "File successfully deleted" << endl << endl;
}
}
【问题讨论】：
-
最可能的解释是
BinaryFile.dat没有存储在您认为的位置，您的程序会将文件保存在当前工作目录中。 -
您确实需要更多的错误检查，这样您才能知道文件是否已打开，并且无论您尝试访问它是否已成功读取/写入数据。
-
我可以验证文件在我使用它时是否存在，它是否已创建等等。问题是当我擦除文件时，我在资源管理器中检查它并且文件是空的- 当我在程序中选择显示结果的选项时，它应该是空白的。相反，它会显示我输入的内容，就好像文件中仍有数据一样。
-
我不认为我的程序实际上是从文件中读取，而是从存储在程序本身中的变量中读取，即使文件是打开的。我希望程序停止从自己的值（即数组 Records EmpRecords[20]）中读取，而是从文件的内容中读取。
-
@user657267 - 我可以验证它是否存储在与程序和源代码相同的目录中，而我正在处理它。问题是程序没有从它实际输入到显示函数中的文件中读取 - 它是从自己的内存中读取。我不知道如何解决这个问题。
标签： c++ fstream binaryfiles