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WAP to print the content of a file in reverse order

C++ Code Example — File Handling Programs

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WAP to print the content of a file in reverse order

Objective

Write a C++ program to print the contents of a file in reverse order.

Algorithm / Approach

  1. Open a file using ifstream.
  2. Move the internal file pointer to the very end of the file: in.seekg(0, ios::end).
  3. Get the total size of the file in bytes: size = in.tellg().
  4. Loop j from 1 to size.
  5. Move the pointer backward one step at a time from the end: in.seekg(-j, ios::end).
  6. Read and print the character at that specific location.
main.cpp 
#include<iostream>
#include<fstream>
using namespace std;
class Test {
 public:
 void rev() {
  char c;
  char name[10];
  ifstream in;
  cout<<"Enter File Name: ";
  cin.getline(name,10);
  in.open(name,ios::in);
  if(!in){
   cout<<"File doesn't exists";
  }
  else {
    in.seekg(0,ios::end);
   int size=in.tellg();

      for (int j=1; j<=size; j++){
          in.seekg(-j, ios::end);
          c=in.get();
          cout<< c;
         }
   }
 in.close();
 }
};
int main() {
 Test t;
 t.rev();
 return 0;
}

Expected Output

Enter File Name: apps.txt
srennigeB rof depoleveD

Explanation of the Program

  • Every open file has an invisible "pointer" that tracks where the next read/write operation will happen.
  • The seekg() (Seek Get) function allows us to manually move this pointer anywhere in the file. tellg() (Tell Get) tells us exactly where the pointer currently is. By moving the pointer backwards from the end (ios::end) and reading one character at a time, we can read the file in reverse.

Complexity

Time Complexity O(n)
Space Complexity O(1)
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