Array Console.WriteLine File For IEnumerable StreamReader

`File.ReadLines`

Large files present complications. If we read their entire contents into memory, we must store it all. This can make programs less efficient.

With ReadLines, we read in a line at a time. This reduces memory usage. For large files, File.ReadLines() is often a better choice—smaller files may be slower overall.

Example

ReadLines() returns an IEnumerable. It reads in a line from the file, and then returns that string. We use it in a For-Each loop—the loop ends when there are no more unread lines.

Here This program reads the data from a "file.txt" that is located in the same directory as the VB.NET executable.

And It displays that data to the screen with Console.WriteLine. Each String can be used in any way.

Imports System.IO

Module Module1
    Sub Main()
        ' Loop over lines in file.
        For Each line As String In File.ReadLines("file.txt")
            ' Display the line.
            Console.WriteLine("-- {0}", line)
        Next
    End Sub
End Module-- This is a text line.
-- This is a second line.

Discussion

For small files, using a Function like File.ReadAllLines is sometimes faster. The memory cost of storing the entire file in memory at once is low.

Tip File.ReadAllLines stores the entire file contents in a String array. File.ReadLines does not.

However For large files, using a Function like File.ReadLines becomes superior. The memory pressure is reduced. Fewer garbage collections occur.

Important For small files, though, the overhead of the enumerator may be more expensive.

Also Some programs require a String array for further processing. In these cases, using ReadAllLines is better.

A summary

File.ReadLines() loads each line of a file into a String. It does not process the entire file at once. Its effect can be duplicated with StreamReader and its ReadLine Function.