如何删除文本文件中存储的数据？
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【中文标题】如何删除文本文件中存储的数据？【英文标题】：How to delete stored data in a text file? 【发布时间】：2021-04-22 11:50:55 【问题描述】：感谢@RemyLebeau，下面的代码基于我原来的代码进行了修改以修复错误。 它很棒，但是出现了一个新问题，当我想使用菜单中的选项 4 删除学生数据时，在输入他们的 ID 后，它说他们的数据已被删除，但事实并非如此。在控制台的末尾，标准错误流 (cerr) 下的消息“从文件读取数据时出错” 不断出现。我所有修复它的尝试都失败了。 error_display
//Project on Student Management
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;
struct Course
string courseName;
string grade;
string status;
;
class Student
int id;
int year;
float cgpa;
vector<Course> courses;
string academic_advisor;
public:
Student();
void getData();
void showData() const;
int getID() const return id;
friend ostream& operator<<(ostream &out, const Student &s);
friend istream& operator>>(istream &in, Student &s);
;
void writeStr(ostream &out, const string &str)
size_t size = str.size();
out.write((char*)&size, sizeof(size));
if (size)
out.write(str.c_str(), size);
void readStr(istream &in, string &str)
str.clear();
size_t size;
if (in.read((char*)&size, sizeof(size)))
if (size > 0)
str.resize(size);
in.read(&str[0], size);
ostream& operator<<(ostream &out, const Course &c)
writeStr(out, c.courseName);
writeStr(out, c.grade);
writeStr(out, c.status);
return out;
istream& operator>>(istream &in, Course &c)
readStr(in, c.courseName);
readStr(in, c.grade);
readStr(in, c.status);
return in;
ostream& operator<<(ostream &out, const Student &s)
out.write((char*)&s.id, sizeof(s.id));
out.write((char*)&s.year, sizeof(s.year));
out.write((char*)&s.cgpa, sizeof(s.cgpa));
writeStr(out, s.academic_advisor);
size_t NumberOfcourses = s.courses.size();
out.write((char*)&NumberOfcourses, sizeof(NumberOfcourses));
for(int i = 0; i < NumberOfcourses; ++i)
if (!(out << s.courses[i]))
break;
return out;
istream& operator>>(istream &in, Student &s)
s.courses.clear();
in.read((char*)&s.id, sizeof(s.id));
in.read((char*)&s.year, sizeof(s.year));
in.read((char*)&s.cgpa, sizeof(s.cgpa));
readStr(in, s.academic_advisor);
size_t NumberOfcourses;
if (in.read((char*)&NumberOfcourses, sizeof(NumberOfcourses)))
s.courses.reserve(NumberOfcourses);
Course c;
for(size_t i = 0; i < NumberOfcourses; ++i)
if (in >> c)
s.courses.push_back(c);
else
break;
return in;
Student::Student()
id = 0;
year = 0;
cgpa = 0.0f;
void Student::getData()
courses.clear();
cout << "\n\nEnter Student Details......\n";
cout << "Enter ID No. : "; cin >> id;
cout << "Enter Intake Year of the Student: "; cin >> year;
cout << "Enter number of Taken courses: ";
size_t NumberOfcourses;
cin >> NumberOfcourses;
cin.ignore();
courses.reserve(NumberOfcourses);
Course c;
for(int a = 0; a < NumberOfcourses; ++a)
cout << "\nEnter Subject Name: ";
getline(cin, c.courseName);
cout << "Enter Grade of Subject: ";
getline(cin, c.grade);
cout << "Enter Subject Status: ";
getline(cin, c.status);
courses.push_back(c);
cout << "Enter student CGPA: ";
cin >> cgpa;
cin.ignore();
cout << endl;
cout << "Enter Name of Academic Advisor of Student: ";
getline(cin, academic_advisor);
void Student::showData() const
cout << "\n\n.......Student Details......\n";
cout << "ID No. : " << id << endl;
cout << "Intake Year : " << year << endl;
cout << "Subjects Taken in Previous Semester : " << endl;
for(size_t t = 0; t < courses.size(); ++t)
cout << "\t" << courses[t].courseName << ": " << courses[t].grade << " (" << courses[t].status << ") ";
cout << endl;
cout << "CGPA : " << cgpa << endl;
cout << "Name of academic advisor of Student : " << academic_advisor << endl;
cout << endl;
void addData()
Student s;
s.getData();
ofstream fout("Students.txt", ios::binary|ios::app);
if (fout << s)
cout << "\n\nData Successfully Saved to File....\n";
else
cerr << "\n\nError Saving Data to File!\n";
void displayData()
ifstream fin("Students.txt", ios::binary);
Student s;
while (fin >> s)
s.showData();
if (fin)
cout << "\n\nData Reading from File Successfully Done....\n";
else
cerr << "\n\nError Reading Data from File!\n";
void searchData()
int n;
cout << "Enter ID Number you want to search for : ";
cin >> n;
ifstream fin("Students.txt", ios::binary);
Student s;
bool flag = false;
while (fin >> s)
if (n == s.getID())
cout << "The Details of ID No. " << n << " are: \n";
s.showData();
flag = true;
break;
if (fin)
if (!flag)
cout << "The ID No. " << n << " not found....\n\n";
cout << "\n\nData Reading from File Successfully Done....\n";
else
cerr << "\n\nError Reading Data from File!\n";
void deleteData()
int n;
cout << "Enter ID Number you want to delete : ";
cin >> n;
ifstream fin("Students.txt", ios::binary);
ofstream fout("TempStud.txt", ios::binary);
ofstream tout("TrashStud.txt", ios::binary|ios::app);
Student s;
bool flag = false;
while (fin >> s)
if (n == s.getID())
cout << "The Following ID No. " << n << " has been deleted:\n";
s.showData();
tout << s;
flag = true;
else
fout << s;
if (fin)
if (fout)
fin.close();
fout.close();
if (!flag)
cout << "The ID No. " << n << " not found....\n\n";
remove("tempStud.txt");
else
remove("Students.txt");
rename("tempStud.txt", "Students.txt");
cout << "\n\nData Successfully Deleted from File....\n";
else
cerr << "\n\nError Saving Data to File!\n";
else
cerr << "\n\nError Reading Data from File!\n";
void modifyData()
int n;
cout << "Enter ID Number you want to Modify : ";
cin >> n;
ifstream fin("Students.txt", ios::binary);
ofstream fout("TempStud.txt", ios::binary);
Student s;
bool flag = false;
while (fin >> s)
if (n == s.getID())
cout << "The Following ID No. " << n << " will be modified with new data:\n";
s.showData();
cout << "\n\nNow Enter the New Details....\n";
s.getData();
flag = true;
fout << s;
if (fin)
if (fout)
fin.close();
fout.close();
if (!flag)
cout << "The ID No. " << n << " not found....\n\n";
remove("TempStud.txt");
else
remove("Students.txt");
rename("TempStud.txt", "Students.txt");
cout << "\n\nData Successfully Updated in File....\n";
else
cerr << "\n\nError Saving Data to File!\n";
else
cerr << "\n\nError Reading Data from File!\n";
void project()
int ch;
do
system("cls");
cout << "...............STUDENT MANAGEMENT SYSTEM..............\n";
cout << "====================SEGI University=================\n";
cout << "0. Exit from Program\n";
cout << "1. Write Data to File\n";
cout << "2. Read Data From File\n";
cout << "3. Search Data From File\n";
cout << "4. Delete Data From File\n";
cout << "5. Modify Data in File\n";
cout << "Enter your choice : ";
cin >> ch;
system("cls");
switch (ch)
case 1: addData(); break;
case 2: displayData(); break;
case 3: searchData(); break;
case 4: deleteData(); break;
case 5: modifyData(); break;
system("pause");
while (ch != 0);
int main()
project();
【问题讨论】：
我在modifyData() 中看到至少一个关于文件名的错字。我强烈建议使用一个带有名称的全局常量而不是重复它，让编译器完成校对的艰苦工作会容易得多。此外，如果您在 Unix 上工作，文件名中的大小写可能无关紧要，但在 Windows 上却很重要。
当您使用调试器运行代码时，一次一行，您看到显示的代码在做什么？
【参考方案1】：
错误是因为 fin （在 deleteData () 函数中）运行到文件末尾，最后 fin 存储 nullptr （布尔转换为 false）这就是 else 语句运行的原因。很明显 while 循环 中断的原因。 要检查文件是否打开，您可以使用 if(fin.is_open()) 用于 fin 并类似地用于 fout，例如 if(fout.is_open())
【讨论】：
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