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Reverse the content of a file and store it in another

  • Difficulty Level : Hard
  • Last Updated : 16 Jul, 2020

The article explains how to store the reverse of the first text file’s data to a second text file. In this post, it has been assumed that there is no text in the first text file. So we will write some text in a first text file by passing data to reverse function and then in reverse function we will copy the reverse of its data to another text file.

Prerequisite:
In text file the data is stored in the ASCII format and the data can be read in the text editor with each alphabet in the file given a specific index in the memory similar to that of an array

Example:

// Sample input 1 
Input to the reverse function:
reverse

Output:
esrever

// Sample input 2
Input to the reverse function:  
Geeks For Geeks

Output:
skeeG roF skeeG

Approach:
Step 1: Calling reverse function with text that is needed to be contained in the first text file i.e. passing sample input of text file.
Working of Reverse function
Step 2: Opening file in writing mode and writing “str” into first text file here: in file Geeks.txt
Step 3: Storing the location of end of first text file in the variable “pos” and the closing the file.
Step 4: Opening first text file in reading mode and placing the reading pointer at position pos.
Step 5: Opening new text file “Geeks2.txt” in writing mode.
Step 6: Reading first text file character by character from the end and storing each character to the second text file.
Step 7: Shifting the read pointer one alphabet backwards in the text file.
Step 8: Closing the text files.
Step 9: Reading second text file (you can skip it if not necessary).

**name of first text file ="Geeks.txt"
**name of second text file="Geeks2.txt"

Example:




#include <conio.h>
#include <fstream.h>
#include <iostream.h>
#include <stdio.h>
  
// function to perform the task
// accepts the parameter str as the text to
// be stored in text file
void reverse(char str[])
{
    char ch;
    ofstream ofs;
  
    // created text file
    ofs.open("Geeks.txt", ios::out);
  
    for (int i = 0; str[i] != '\0'; i++) {
        // writing into the file
        ofs.put(str[i]);
    }
  
    // storing the position of  end of the file
    int pos = ofs.tellp();
    ofs.close();
  
    // object for reading the contents of the
    // first text file
    ifstream ifs;
    ifs.open("Geeks.txt", ios::in);
  
    // object for writing in to the text file 2
    ofstream ofs1;
    ofs1.open("Geeks2.txt", ios::out);
  
    // putting the read pointer to the last alphabet
    // of the file
    ifs.seekg(--pos);
  
    while (pos >= 0) {
        // reading from the file 1
        ifs.get(ch);
  
        // writing to the file 2
        ofs1.put(ch);
  
        /* shifting read pointer position one 
        alphabet backwards in the text file */
        pos--;
  
        ifs.seekg(pos);
    }
  
    ifs.close();
    ofs1.close();
  
    ifstream ifs1;
    ifs1.open("Geeks2.txt", ios::in);
  
    // file.eof() checks the end of the text file
    while (!ifs1.eof()) {
        ifs1.get(ch);
        cout << ch;
    }
    ifs1.close();
}
  
// Driver code
int main()
{
    clrscr();
  
    // sample input 1
    cout << "example 1: (Geeks For Geeks) \n";
  
    // passing first text file's text
    // through reverse function
    reverse("Geeks For Geeks");
  
    // sample input 2
    cout << "\n example 2:(reverse)\n";
    reverse("reverse");
  
    getch();
    return 0;
}

Output:

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