We Keep Coding

C#: How to read a file that's in use by another process

There is one text file in hard drive which continuously writing by some application XYZ.
Now, from application ABC, I am trying to read the file, but I am getting error,
the process cannot access the file because it is being used by another process
Note - I don't have control over XYZ application, still is there any way to read the file from application ABC?
byte[] data = File.ReadAllBytes(File.FullName)

Access the file in read mode so that you will not get this error.
Try this solution
How do I open an already opened file with a .net StreamReader?

How to close a file after creating it

I am coding in C# for the first time and encountering this.
I use the function File.WriteAllBytes(OutputFileName, dest); which is creating a file on the disk and when my application tries to open the same file using file.Open giving me an exception Access to Path Denied. Please help me to get rid of this. I am on Windows 7, not running as administrator.
Thank you.

The file is closed. It is denied for other reasons. Check the path, or maybe you could open it with FileMode File.Open(path, FileMode.Open). Otherwise check your permissions.
Given a byte array and a file path, this method opens the specified file, writes the contents of the byte array to the file, and then closes the file.
Source

The method WriteAllBytes closes the file after writing the byte array to the file so I guess your problem lies elsewhere.
Definition:
Creates a new file, writes the specified byte array to the file, and then closes the file. If the target file already exists, it is overwritten.
More reading on the method: File.WriteAllBytes Method
Robert was ahead of me.. :)

A couple of things spring to mind:
Where are you saving the file to? Windows 7 seems to picky about saving to the root of C:\ these days.
Permissions issue.

How to detect real-time change of text files?

I am stating to write a little PC tool to read log files using c# or java. The log files will be in .txt format. An application is running and writing logs, and I want my tool to open the log at the same time and refresh automatically when a new line is written to the log file.
My challenge is, how do I detect the log file changes so that my tool will have real-time displaying ability? This is a general question but pseudo codes will be greatly appreciated!

You can use the FileSystemWatcher class (MSDN page). Be careful though, if you try to open the file while the other process is writing the file you will probably be denied access.

There's a bunch of this questions here, and answers too:
Reading file content changes in .NET
Your target is FileStream object, I suppose.

I would poll the file and check it's metadata for the last changed date, or if you're using .NET, you could use the FileSystemWatcher class

How to detect a file is in use?

I had searched a lot of examples, but none work perfect for me. I am using C#.
My application need to remove the files in folder, only when the file is closed.
The try-catch File.Open(...) method only works for certain filetype like doc, xls, ppt, pdf, mp3 etc, but not work for txt, zip, html etc...

The behavior your are seeing doesn't have anything to do with the file's extension or contents. It has to do with the way the associated applications treat those files. For example, Notepad, Internet Explorer, etc will not hold a lock on an opened file once the contents are read. That's why .txt and .html files are able to be opened.
Microsoft Office, virtually all media players, etc will hold a lock on the file. In the case of Office, it's doing so to make sure other programs don't delete/move the file out from under it. In the case of a media player, the files are usually too big to be read into memory completely. That's why those file types are locked when in use.
In other words, those files that appear to not be in use aren't actually in use. The program read the data from the file and close it and now it's done with it. There's really no easy way to determine whether or not another program has a particular file open if it no longer has an open handle to the file.

Open the file in the binary mode File.Open(...) will work for all files.

Try opening the file in write mode, I think there is something to specify that the lock is exculsive..but for some reason if your thread dies..dunno if that lock will be released automatically...

all you need is to delete the file that is not in use ... rigth ... Simply ignore the exception thrown by File.Delete. Since it will not delete the file that is in use ..
try
{
File.Delete(path);
}
catch(Exception e)
{
// ignore ... or whatever action
}
you can also catch specific exceptions to take specific action ... like IOException for file in use, UnauthorizedAccessException for read only files and permission issues etc ...
Checking file for opening and then trying to delete may still through exception as file may have been opened by some process between checking and deleting operations ..

Write to file that is open in Excel

Suppose I have a program running that periodically adds information to a .CSV file. Is there a way to write to the file while it is already open in Excel? Obviously the changes wouldn't be noticed until the file was re-opened in Excel, but as it stands right now, I'm catching IOException and just starting a new .csv file if the current one is already open.

Excel seems to open the file in exclusive mode, so the only way I can think of would be to write your changes to a temporary file, and then use FileSystemWatcher to see when the file is closed, and overwrite the file.
Not a very good idea, as you could lose data. The whole reason excel locks the file is so that you don't accidentally overwrite changes made in excel.

It sounds like the file is locked. I doubt you will be able to write to that file if it is open in another process.

As a former (and sort of current) VB Programmer, I can tell you Jared is correct - there is no way to do this directly. You can try to copy the file first, make your edits, then attempt to save the file back to its original location until the locked file becomes free. You should be able to copy that file, even while locked.

What about using Excel's object model and automating the addition of the data into the open spreadsheet? You'd probably need to prompt the user somehow to let them know what was happening.