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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?

Unable to save to nul device from ASP.net app

I am having a spot of bother trying to save a dummy file to the nul device in an ASP.Net (.Net 4.5.2) application. When I get the the point where the application tries to save the file, it throws an exception.
The file's path is set to "nul" (sic), and when it is saved I get the following exception message:
Access denied to file "\\\\.\\nul"
Is it possible using .Net (C# in my case) to save a file to the nul device from within a web application?
In case you are wondering, saving the file is merely a trigger for another action. I am not interested in the saved file itself, and I want to avoid the code overhead of having to create and later delete a uniquely named dummy file - hence saving it to the nul device.
TIA

This answer on MSDN suggests you can't do this with the .NET file handling API:
While the Win32 CreateFile method will open devices, alternate streams, etc, somewhere along the line it was decided that the .Net File implementation would be restricted to traditional files. Probably not what you wanted to hear.
social.msdn.microsoft.com/Forums/vstudio/en-US/43163abb-4e82-4a7d-b614-29eb7914bdba/nul-filename-in-net

use the flag that deletes filestream on close...
new FileStream(TempFileName,
FileMode.CreateNew,
FileAccess.ReadWrite,
FileShare.ReadWrite, 512,
FileOptions.DeleteOnClose);

C# Copy a File That is Being Written To

I have read many other posts about this topic, but none appear to solve my problem directly (which surprises me).
Regardless...I wrote a log parser and very simply I am looking to copy a file from a remote machine locally, prior to parsing it. The file I am trying to copy is being written to constantly and I have ‘random’ success in copying it. Sometimes it will work and other times I will get an ‘access is denied’ or FileAccess error. A few other points:
Whenever I use windows explorer to copy the file locally, I never
have a problem copying it (which leads me to believe it’s perfectly
possible to copy the file 100% of the time).
I can always open the file using a text editor in its remove location.
I do not own the file being written to and do not wish to ‘lock’ it in anyway such that the application that is actually writing to this file fails.
Does anyone have any suggestions for how to copy this file?
The current command I am using is:
File.Copy(this.txt_log_file_to_analyze.Text, sLogFileToAnalyze,true);

I guess you'll have to open the file using:
File.Open(this.txt_log_file_to_analyze.Text,FileMode.Open,FileAccess.Read,FileShare.ReadWrite)
and then copy the contents of the file 'manually' i.e.
using (var from = File.Open("path", FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
using (var to = File.OpenWrite("to_path"))
{
from.CopyTo(to);
}
or if .NET 4.5 see How do I copy the contents of one stream to another?
Using the above api, you can specify that you do not want exclusive access to the file.

Keep file restricted from opening it by anyone

I have an application in c#.net in which I have embeded the SWF file in SWFObject from COM Object.
Now after installation, the original SWF file also available in the application root directory. So from that place(application root directory) anyone can access that file. But I want to restrict that file from being opened.
axShockwaveFlash1.Movie = Directory.GetCurrentDirectory() + "\\XYZ.swf";
I did something like this.
So how can I restrict that file in application root directory such that only from my application I can access it..??

You can embed the file into a dll or exe file and play it from there. this way it is not (as a seperate file) in the file system at all.
For details see How to embed and access resources by using Visual C#.

You could save the swf file binary data as static bytes in your code and statically load them and convert back to an swf file. The conversion might take a little while but it only occurs once as you open the program.
Edit:
But k3b's answer is better.

Permissions are based on users, not applications, so the short answer is you can't. However, you can build your own application-specific authentication pretty easily. Have your SWF require specific FlashVars to be set in order to move beyond frame 1. People can still decompile your SWF but this will at least stop most people. Another option is to try to store the data within you binary somehow and load the SWF using a byte-array, see this post for one attempt at that.

Save data in executable

I have a portable executable that saves data to a file in the same folder as the executable. Is there any way that I can save data into the executable itself when I close the app?
This maybe weird, but taking the data with me and only have one file for the exe and data would be great.
Would prefer if this was made with C#, but is not a requisite.

You cannot modify your own EXE to contain stored data in anything approaching an elegant or compact way. First off, the OS obtains a lock on the EXE file while the application contained within is being run. Second, an EXE comes pre-compiled (into MSIL at least), and modification of the file's source data usually requires recompilation to reset various pointers to code handles, or else a SERIOUS knowledge on a very esoteric level about what you're doing to the file.
The generally-accepted methods are the application config file, a resource file, or some custom file you create/read/modify at runtime, like you're doing now. Two files for an application should not be cause for concern

You can, by reserving space through the means of using a string resource and pad it out. You need to do a bit of detective work to find out exactly where in the offset to the executable you wish to dump the data into, but be careful, the file will be "in use", so proceed cautiously with that.

So right now you're using an app.config (and Settings.settings) file?
I believe this is the most compact way to save data close to the .exe.
I would highly doubt you can alter the manifest of the .exe, or any other part of it.
Edit: Apparently, there might be some ways after all: http://www.codeproject.com/KB/msil/reflexil.aspx

There is one way using multiple streams, but only works in NTFS filesystems.
NTFS allows you to define alternative "named" streams in one file. The usual content is in the main = unnamed stream. It has something to do with the extra info you can see when you right click a file and check properties.
Unfortunatly C# has no support for multiple streams, but there are open source pojects that can help you.
See this link for a nice wrapper to read and write multiple streams to one single file in C#

Alternate data streams might work. By using the ::stream syntax you can create a data stream within your exe and read/write data.
Edit:
to create/access an alternate data stream, you will use a different filename. Something like:
applicAtion.exe:settings:$data
this will access a data stream named "settings" within application.exe. To do this you need to add the :settings:$data to the filename when reading or writing to the file. This functionality is provided by ntfs so it shold work in c# and should work when the application is running.
Additional information is available at: http://msdn.microsoft.com/en-us/library/aa364404(VS.85).aspx

If you want to take the data with you and only have one file for the exe and data, .zip them into a self-extracting .exe.

you can add data to end of executable file :
var executableName = Process.GetCurrentProcess().MainModule.FileName;
// rename executable file
var newExecutableName = fullPath.Replace(".exe", "_.exe");
FileInfo fi = new FileInfo(executableName);
fi.MoveTo(newExecutableName);
// make copy of executable file to original name
File.Copy(newExecutableName, executableName);
// write data end of new file
var bytes = Encoding.ASCII.GetBytes("new data...");
using (FileStream file = File.OpenWrite(executableName))
{
file.Seek(0, SeekOrigin.End);
file.Write(bytes, 0, bytes.Length);
}
// we can delete old file when exited