My data show up 2 twice whil use function? Operation file C++ - Case: Delete Specific Line in c++

Question

I got a task that is: Write a simple program that can be used to delete data on one one line specified in a file with the following steps:  Manually create a file containing:

i.  Fill from line 1
ii. Fill from line 2
ii. Fill from line 3
iv. Fill in line 4

 Display the entire contents of the file.  Appears the choice of how many rows to delete.  Delete data in the selected row.  Display the entire contents of the file.

I have created the program as below:

#include <iostream>
#include <string>
#include <fstream>
using namespace std;
// Function Prototipe
void garis();
void show_databefore();
void show_data();
void del_line(const char *file_name, int n);
// Variable Declaration
int n;
ifstream myFile;
string output,buffer;
// Main Function
int main(){
    cout << "Show data and delete specific line Program " << endl;
    garis ();
    cout << "The Data " << endl;
    show_databefore();
    garis();
    
    cout << "Select the Rows of data you want to delete: ";
    cin >> n;
    cout << "\nBefore " << endl;
    // If Case after input n
    if((0 < n) && (n < 100)){
        del_line("data1.txt", n);  // this process will delete the row that has been selected.
    } else {
        cout << "Error" << endl;} 
    show_data(); // when calling this function. Display on the console, data is displayed 2 times.
    return 0;
}


//Function to delete data in the row that has been selected
void del_line(const char *file_name, int n){    
  ifstream fin(file_name);    
  ofstream fout;                
  fout.open("temp.txt", ios::out); 
  
  char ch; 
  int line = 1;            
  while(fin.get(ch)) 
  {      
    if(ch == '\n') 
      line++; 
     
    if(line != n)      
      fout<<ch; 
  } 

  fout.close();  
  fin.close();   

  remove(file_name);        
  rename("temp.txt", file_name);  
} 

// Function to display data1.txt to the console
void show_databefore(){
    myFile.open("data1.txt");
    while (!myFile.eof()){
        getline(myFile,buffer);
        output.append("\n" + buffer); 
    }
    cout << output << endl;
    myFile.close(); 
}
// Function to display data1.txt to the console  T
// This fuction actually same as show_databefore. 
void show_data(){
    myFile.open("data1.txt");
    while (!myFile.eof()){
        getline(myFile,buffer);
        output.append("\n" + buffer); 
    }
    cout << output;
    myFile.close(); 
}
//Function to provide a boundary line.
void garis(){
    cout << "======================================================= " << endl << endl;
}

When I run my program it works, but when I bring up data to the console, my data appears 2 times and I've tried the method without using the function. However, the result remains the same.

Here is the result

Can anyone help me? Or maybe there's an easier way to build my program? Thank you

Answer 1

This code is bugged in two different ways

void show_data(){
    myFile.open("data1.txt");
    while (!myFile.eof()){
        getline(myFile,buffer);
        output.append("\n" + buffer); 
    }
    cout << output;
    myFile.close(); 
}

The first bug is the incorrect use of eof. The second bug is the use of the global variable output. The code assumes that the variable is an empty string when the function is entered, but because it's a global variable there is no way to ensure this. Here's a fixed version, the global variable is now a local variable and the eof problem has been fixed.

void show_data(){
    string output; // local variable
    myFile.open("data1.txt");
    while (getline(myFile,buffer)){
        output.append("\n" + buffer); 
    }
    cout << output;
    myFile.close(); 
}

Don't needlessly use global variables, they are a huge source of bugs, as well as many other problems. There are several others in your code. They should all be removed.