How to read a file in reverse order using C++ [duplicate]

Answer 1

Yes, but you basically have to do it manually.

The basic algorithm is as follows:

1. Seek to the end of the file with is.seekg(0, is.end)
2. Determine the file size with is.tellg()
3. Repeatedly seek backwards and read chunks of the file until you reach the front

Answer 2

Just use the seekg and related functions in istream class. Here is a working example. Tested.

#include <fstream>
#include <iostream>

using namespace std;

int main()
{
    ifstream in("file.txt");

    // Get the length of the file
    in.seekg(0, in.end);
    int len = in.tellg();

    // Start reading the file in reverse
    char c;
    while (len--) 
    {
        in.seekg(len, in.beg);
        in >> c;
        cout << c;

    }
}

Answer 3

If the file is small enough so the entire contents easily fit within memory, it will be both far faster and far easier to code to read the file forward into a string and then reversing that string after the fact.

If the contents won't fit in memory, you'll have to use nneonneo's solution. It would probably be best to turn off buffering.