How to read a text file reversely with iterator in C#

Question

I need to process a large file, around 400K lines and 200 M. But sometimes I have to process from bottom up. How can I use iterator (yield return) here? Basically I don\'t l

Answer 1

Attention: this approach doesn't work (explained in EDIT)

You could use File.ReadLines to get lines iterator

foreach (var line in File.ReadLines(@"C:\temp\ReverseRead.txt").Reverse())
{
    if (noNeedToReadFurther)
        break;

    // process line here
    Console.WriteLine(line);
}

EDIT:

After reading applejacks01's comment, I run some tests and it does look like .Reverse() actually loads whole file.

I used File.ReadLines() to print first line of a 40MB file - memory usage of console app was 5MB. Then, used File.ReadLines().Reverse() to print last line of same file - memory usage was 95MB.

Conclusion

Whatever `Reverse()' is doing, it is not a good choice for reading bottom of a big file.