如何解决如何显示我输入到文本文件中的所有数据?
以下是将学生的一些详细信息输入文本文件的代码,用户可以从主菜单中使用选项 2 显示它们。
我的问题在于它应该显示所有“学生选修的课程”的部分。
当我选择显示所有数据时,“使用 the for loop
提到的部分仅显示我在写入文件时输入的最后一个值。
我怎样才能让它显示我所有的条目?
问题出在 showdata
和 displaydata
函数下。
//Project on Student Management
#include<iostream>
#include<fstream>
#include<iomanip>
#include<stdlib.h>
using namespace std;
class Student
{
int id;
int year;
char grade[50];
float cgpa;
int NumberOfcourses;
char courseName[100];
char academic_advisor[100];
char status[100];
public:
void getData();
void showData();
int getID(){return id;}
}s;
void Student::getData()
{
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: ";
cin >> NumberOfcourses;
for(int a=1; a<=s.NumberOfcourses; a++)
{
cout<<"\nEnter Subject Name: ";
cin.ignore();
cin.getline(courseName,100);
cout << "Enter Grade of Subject: ";
cin >> grade;
cout<<"\nEnter Subject Status: ";
cin.ignore();
cin.getline(status,100);
}
cout << "Enter student CGPA: ";
cin >> s.cgpa;
cout << endl;
cout << "Enter Name of Academic Advisor of Student: "; cin.ignore();
cin.getline(s.academic_advisor,100);
}
void Student::showData()
{
cout << "\n\n.......Student Details......\n";
cout << "ID No. : " << id << endl;
cout << "Intake Year : " << year << endl;
cout << "Subjects Taken in PrevIoUs Semester : " << endl;
for(int t=1; t<=NumberOfcourses; t++)
{
cout << "\t" << courseName << ": " << grade << " ("<< status << ") ";
cout << endl;
}
cout << "CGPA : " << cgpa << endl;
cout << "Name of academic advisor of Student : " << academic_advisor << endl;
cout << endl;
}
void addData()
{
ofstream fout;
fout.open("Students.txt",ios::out|ios::app);
s.getData();
fout.write((char*)&s,sizeof(s));
fout.close();
cout<<"\n\nData Successfully Saved to File....\n";
}
void displayData()
{
ifstream fin;
fin.open("Students.txt",ios::in);
while(fin.read((char*)&s,sizeof(s)))
{
s.showData();
}
fin.close();
cout<<"\n\nData Reading from File Successfully Done....\n";
}
void searchData()
{
int n,flag=0;
ifstream fin;
fin.open("Students.txt",ios::in);
cout<<"Enter ID Number you want to search for : ";
cin>>n;
while(fin.read((char*)&s,sizeof(s)))
{
if(n==s.getID())
{
cout<<"The Details of ID No. "<<n<<" are: \n";
s.showData();
flag++;
}
}
fin.close();
if(flag==0)
cout<<"The ID No. "<<n<<" not found....\n\n";
cout<<"\n\nData Reading from File Successfully Done....\n";
}
void deleteData()
{
int n,flag=0;
ifstream fin;
ofstream fout,tout;
fin.open("Students.txt",ios::in);
fout.open("TempStud.txt",ios::out|ios::app);
tout.open("TrashStud.txt",ios::out|ios::app);
cout<<"Enter ID Number you want to delete : ";
cin>>n;
while(fin.read((char*)&s,sizeof(s)))
{
if(n==s.getID())
{
cout<<"The Following ID No. "<< n <<" has been deleted:\n";
s.showData();
tout.write((char*)&s,sizeof(s));
flag++;
}
else
{
fout.write((char*)&s,sizeof(s));
}
}
fout.close();
tout.close();
fin.close();
if(flag==0)
cout<<"The ID No. "<< n <<" not found....\n\n";
remove("Students.dat");
rename("tempStud.txt","Students.txt");
}
void modifyData()
{
int n,flag=0,pos;
fstream fio;
fio.open("Students.txt",ios::in|ios::out);
cout<<"Enter ID Number you want to Modify : ";
cin>>n;
while(fio.read((char*)&s,sizeof(s)))
{
pos=fio.tellg();
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();
fio.seekg(pos-sizeof(s));
fio.write((char*)&s,sizeof(s));
flag++;
}
}
fio.close();
if(flag==0)
cout<<"The ID No. "<<n<<" not found....\n\n";
}
void project()
{
int ch;
do
{
system("cls");
cout<<"...............STUDENT MANAGEMENT SYstem..............\n";
cout<<"======================================================\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);
}
int main()
{
project();
}
解决方法
您的 Student
班级只能保存 1 组课程信息。您的 getData()
循环一遍又一遍地覆盖相同的变量,这就是为什么您只能看到输入的最后一门课程。您需要分配一个数组(或者更好,使用std::vector
)来为每个Student
保存多个课程。
您的代码还有其他问题。
尝试更像这样的事情:
//Project on Student Management
#include <iostream>
#include <fstream>
using namespace std;
struct Course
{
char courseName[100];
char grade[50];
char status[100];
};
class Student
{
int id;
int year;
float cgpa;
int NumberOfcourses;
Course *courses;
char academic_advisor[100];
public:
Student();
~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);
};
ostream& operator<<(ostream &out,const Course &c)
{
out.write(c.courseName,sizeof(c.courseName));
out.write(c.grade,sizeof(c.grade));
out.write(c.status,sizeof(c.status));
return out;
}
istream& operator>>(istream &in,Course &c)
{
in.read(c.courseName,sizeof(c.courseName));
in.read(c.grade,sizeof(c.grade));
in.read(c.status,sizeof(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));
out.write(s.academic_advisor,sizeof(s.academic_advisor));
out.write((char*)&s.NumberOfcourses,sizeof(s.NumberOfcourses));
for(int i = 0; i < s.NumberOfcourses; ++i)
{
out << s.courses[i];
}
return out;
}
istream& operator>>(istream &in,Student &s)
{
delete[] s.courses;
s.courses = NULL;
s.NumberOfcourses = 0;
in.read((char*)&s.id,sizeof(s.id));
in.read((char*)&s.year,sizeof(s.year));
in.read((char*)&s.cgpa,sizeof(s.cgpa));
in.read(s.academic_advisor,sizeof(s.academic_advisor));
int NumberOfcourses;
if (in.read((char*)&NumberOfcourses,sizeof(NumberOfcourses)))
{
s.courses = new Course[NumberOfcourses];
for(int i = 0; i < NumberOfcourses; ++i)
{
if (in >> s.courses[i])
s.NumberOfcourses++;
else
break;
}
}
return in;
}
Student::Student()
{
id = 0;
year = 0;
cgpa = 0.0f;
NumberOfcourses = 0;
courses = NULL;
academic_advisor[0] = '\0';
}
Student::~Student()
{
delete[] courses;
}
void Student::getData()
{
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: ";
cin >> NumberOfcourses;
cin.ignore();
delete[] courses;
courses = new Course[NumberOfcourses];
for(int a = 0; a < NumberOfcourses; ++a)
{
cout << "\nEnter Subject Name: ";
cin.getline(courses[a].courseName,100);
cout << "Enter Grade of Subject: ";
cin.getline(courses[a].grade,50);
cout << "\nEnter Subject Status: ";
cin.getline(courses[a].status,100);
}
cout << "Enter student CGPA: ";
cin >> cgpa;
cin.ignore();
cout << endl;
cout << "Enter Name of Academic Advisor of Student: ";
cin.getline(academic_advisor,100);
}
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(int t = 0; t < NumberOfcourses; ++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)
cerr << "\n\nError Reading Data from File!\n";
else
cout << "\n\nData Reading from File Successfully Done....\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)
{
cerr << "\n\nError Reading Data from File!\n";
}
else
{
if (!flag)
cout << "The ID No. " << n << " not found....\n\n";
cout << "\n\nData Reading from File Successfully Done....\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 << " will be deleted:\n";
s.showData();
tout << s;
flag = true;
}
else
{
fout << s;
}
}
if (!fin)
{
cerr << "\n\nError Reading Data from File!\n";
}
else if (!fout)
{
cerr << "\n\nError Saving Data to File!\n";
}
else
{
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";
}
}
}
void modifyData()
{
int n;
cout << "Enter ID Number you want to Modify : ";
cin >> n;
ifstream fin("Students.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)
{
cerr << "\n\nError Reading Data from File!\n";
}
else if (!fout)
{
cerr << "\n\nError Saving Data to File!\n";
}
else
{
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";
}
}
}
void project()
{
int ch;
do
{
system("cls");
cout << "...............STUDENT MANAGEMENT SYSTEM..............\n";
cout << "======================================================\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();
}
或者:
//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,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,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.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 << "\nEnter Subject Status: ";
getline(cin,c.status);
s.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","Students.txt");
cout << "\n\nData Successfully Updated in File....\n";
}
}
}
void project()
{
int ch;
do
{
system("cls");
cout << "...............STUDENT MANAGEMENT SYSTEM..............\n";
cout << "======================================================\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();
}
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