FileInfo.CopyTo() throws exception when trying to overwrite file

Question

I have the following piece of code in a .NET 6 app that copies some files to a different destination on the file system:

DirectoryInfo targetDir = GetTargetDir();
foreach (FileInfo fi in GetFilesToCopy())
{
    fi.CopyTo(Path.Combine(targetDir.FullName, fi.Name), true);
}

As you can see, I'm passing true to the .CopyTo() method, so it overwrites the file if it already exists.
However, this seems to not work properly:

If the destination file does NOT exist, the copy works fine
If the destination file DOES exist, however, the copy operation fails and throws a UnauthorizedAccessException with an error message like 'Access to the path 'C:\my destination dir\my destination file.ext' is denied.'

I've checked the method documentation, and it says that that exception is thrown if the destination is a directory or if we're trying to copy to a different drive. However, I'm not doing any of those things (and anyway it doesn't explain why it works if the file does not exist)

I've checked all I could think of, and it all seems in order:

The user running the application has permission to write to that location and is the owner of the existing files
The files are not in use, I can easily delete them using windows explorer or cmd
I've also tried running the code as administrator (even though it shouldn't be needed) but same error occurs

Can anyone tell me why this is happening?

Is the (existing) file read-only? Please check theese two: https://stackoverflow.com/questions/18554108/c-sharp-unauthorizedaccessexception-in-file-copy and https://stackoverflow.com/questions/8821410/why-is-access-to-the-path-denied — nilsK, Jun 08 '22 at 14:17
@nilsK: thanks, that was it, I had to remove the ReadOnly attribute. Do you know why the CopyTo() method sets the ReadOnly attribute when copying a file? Any way to avoid it? — Master_T, Jun 08 '22 at 14:43
If I am not wrong, you are trying to store the file to `C:` root level. To store file at `C:\` root level, you may have to run your process as `An Administrator`. I think if you try to store it under user's folder such as `c:\users\[username]\my_destination_dir\my_destination_file.ext`, then it should work. — S.Mishra, Jun 08 '22 at 14:45
@S.Mishra: no, if you read my question you'll see I've already tried running as admin. The problem was a readonly attribute on the files. — Master_T, Jun 08 '22 at 14:51
@Master_T glad i could help. To your question: no i have no clue. It's a feature? ;) — nilsK, Jun 09 '22 at 14:49
@nilsK: I've done some more research, and apparently it just preserves the origin files' attributes. — Master_T, Jun 09 '22 at 15:40

score 0 · Accepted Answer · answered Jun 08 '22 at 14:50

Apparently the problem was the files have the Read Only attribute (thanks to @nilsK for pointing me in the right direction).

I've resolved this with the following code:

string destFile = Path.Combine(targetDir.FullName, fi.Name);
if (File.Exists(destFile))
{
    File.SetAttributes(destFile, FileAttributes.Normal);
}

fi.CopyTo(destFile, true);

FileInfo.CopyTo() throws exception when trying to overwrite file

1 Answers1