How to skip reading text file in C# without using looping

Question

1.00/5 (1 vote)

See more:

How to skip reading log/text files line. Suppose today my log file having 1000 nos of line. I have read it completely already. So i need to keep that line no as bookmarks and i am able to get that line no as well. And next day my log file change and added 2000 no of lines. So i don't want to read it from start i need to read it from 1001 to 2000. So how to do that without using any looping because if i am using looping then its again reading from start to end. Please help me on this.

Posted 16-Mar-15 1:38am

SanSkun

Add a Solution

Comments

Nathan Minier 16-Mar-15 7:50am

You could add a little metadata to the file, maybe a header with a "lastLineRead" property so that you know where it was left off the previous day.

That'd require some thought as to certain logging mechanisms, such as clearing, but would work as you're describing.

[no name] 16-Mar-15 13:15pm

Read this: http://stackoverflow.com/a/21307627/4320056

2 solutions

Solution 2

Solution 1:
Rename the log file before you read it, e.g. by adding the date into the filename, and then read it. The new entries then get logged into a new empty log file. That way you won't have to track anything.

Solution 2:
When reading the log file you probably use a StreamReader and call ReadLine() repeatedly in a loop? You can get the byte-position of the StreamReader in the file via StreamReader.BaseStream.Position. I'm not 100% sure that this matches the end of the last line read exactly but if it doesn't it will be "very close". Save that position somewhere - in an extra file or in a database - and when you open the logfile the next time, seek the BaseStream ahead to that position before starting to ReadLine().

Posted 16-Mar-15 1:53am

manchanx

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Hardeep Saggi · Accepted Answer · 2015-03-16T01:48:00

Solution 1

You can use this:

C#

var lines = File.ReadLines(ofd.FileName);
foreach (string line in lines.Skip(8))
    Trace.WriteLine(line);

XML

Because the File.ReadLines returns an IEnumerable<string>, the lines are only loaded when iterated.

Also check File.ReadLines Method http://msdn.microsoft.com/en-us/library/dd383503.aspx

Happy coding Hours ;_)

Posted 16-Mar-15 1:48am

Hardeep Saggi

Comments

[no name] 16-Mar-15 8:30am

"Because the File.ReadLines returns an IEnumerable<string>, the lines are only loaded when iterated."

..Yes - only loaded when iterated. What happens when you .Skip() ?

[no name] 16-Mar-15 13:14pm

Read this: http://stackoverflow.com/a/21307627/4320056

Mario Z 16-Mar-15 16:53pm

I don't get how this answer got upvoted and @manchanx downvoted, that doesn't make any sense because this is plain wrong.
Yes it is true that with ReadLines lines are only loaded when iterated, but what do you think that Skip method does, not iterate through lines?

This is literally how Skip extension method looks:

using (IEnumerator<tsource> e = source.GetEnumerator())
{
while (count > 0 && e.MoveNext()) count--;
if (count <= 0)
while (e.MoveNext()) yield return e.Current;
}

In other words you will read each and every single line and each line will create appropriated string value.
The @manchanx second suggestion is a direction to the right path.