C ++删除文件中的文本行 [英] C++ deleting line of text in a file

问题描述

我的c ++程序有一个问题...我的整个程序是一个数据库的学生的名字，年级和年龄，我有一个问题的功能，当用户想删除1个学生的数据。这里是代码：

I have a problem with my c++ program... My whole program is a database for student names, grades and ages and I have a problem with function when user wants to delete data for 1 student. Here is the code:

void deletestudentdata()
{
    string name, grade, tname;
    int age, x=0; // x - "counter" to check if user entered wrong name

    system("cls");
    cout << "Enter name of the student you want to erase from database" << endl;
    cin >> tname;

    ifstream students("students.txt");
    ofstream temp("temp.txt"); // temp file for input of every student except the one user wants to delete

    while(students >> name >> grade >> age)
    {
        if(tname!=name){ // if there are students with different name, input their data into temp file
            temp << name << ' ' << grade << ' ' << age << endl;
        }
        if(tname==name){ // if user entered correct name, x=1 for later output message that the user data has been deleted
            x=1;
        }
    }
    students.clear(); // clear eof and fail bits
    students.seekg(0, ios::beg);
    students.close();
    temp.close();
    remove("students.txt"); 
    rename("temp.txt","students.txt");
    if(x==0){ // x was set to 0 at start, so if it didn't change, it means user entered the wrong name
        cout << "There is no student with name you entered." << endl;
    }
    else{ // x is not 0, it means user entered the correct name, print message that students data has been deleted
        cout << "Student data has been deleted." << endl;
    }
}

它可以工作，但问题是我进入学生数据，当我想通过此功能删除它不删除它，我首先必须关闭程序，然后重新打开程序，然后调用该函数，所以它删除学生的数据。

It works, but the problem is that I enter student data and when I want to delete it via this function it doesn't delete it, I first have to close the program and then reopen the program and then call that function so it deletes students data.

如何更改它，以便我可以在输入后立即删除学生数据，而无需先关闭程序？

How can I change it so I can delete students data right after inputing, without having to close the program first?

推荐答案

像这样。它的eaiser显示的代码比解释。

Like this. Its eaiser to show the code than to explaine.

#include <string>
#include <vector>
#include <fstream>
#include <iostream>
using namespace std;




void displaystudentdata()
{
   string name, grade, tname;
    int age, x=0; // x - "counter" to check if user entered wrong name

    system("cls");

    ifstream students("students.txt");


    cout<<"-------------------------------------------------------------------\n\n";
    while(students >> name >> grade >> age)
    {

        cout<<"Name= "<<name <<", Grade= "<< grade <<" , Age= " <<age<<"\n";
    }
    students.clear(); // clear eof and fail bits
    students.seekg(0, ios::beg);
     students.close();
}

void deletestudentdata()
{
    string name, grade, tname;
    int age, x=0; // x - "counter" to check if user entered wrong name



    ifstream students("students.txt");
    ofstream temp("temp.txt"); // temp file for input of every student except the one user wants to delete


    cout<<"-------------------------------------------------------------------\n\n";

    cout << "Enter name of the student you want to erase from database >" << endl;
    cin >> tname;

    //ifstream students("students.txt");
    //ofstream temp("temp.txt"); // temp file for input of every student except the one user wants to delete

    while(students >> name >> grade >> age)
    {
        if(tname!=name){ // if there are students with different name, input their data into temp file
            temp << name << ' ' << grade << ' ' << age << endl;
        }
        if(tname==name){ // if user entered correct name, x=1 for later output message that the user data has been deleted
            x=1;
        }
    }
    students.clear(); // clear eof and fail bits
    students.seekg(0, ios::beg);
    students.close();
    temp.close();
    remove("students.txt"); 
    rename("temp.txt","students.txt");
    if(x==0){ // x was set to 0 at start, so if it didn't change, it means user entered the wrong name
        cout << "There is no student with name you entered." << endl;
    }
    else{ // x is not 0, it means user entered the correct name, print message that students data has been deleted
        cout << "Student data has been deleted." << endl;
    }
}


int main(void)
{



  displaystudentdata();
  deletestudentdata();
  displaystudentdata();
  cout << "Student data has been deleted. \n\n" << endl;
  cout<<" \nPress any key to continue\n";
  cin.ignore();
  cin.get();

   return 0;
}

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