Ignoring exceptions

Question

I have some code which ignores a specific exception.

try
{
    foreach (FileInfo fi in di.GetFiles())
    {
        collection.Add(fi.Name);
    }
    foreach (DirectoryInfo d in di.GetDirectories())
    {
        populateItems(collection, d);
    }
}
catch (UnauthorizedAccessException ex)
{
   //ignore and move onto next directory
}

of course this results in a compile time warning as ex is unused. Is there some standard accept noop which should be used to remove this warning?

Answer 1

Just rewrite it as

catch (UnauthorizedAccessException) {}

Answer 2

I usually do

Debug.WriteLine(ex.message)

(that way I can just set a breakpoint in the exception, if needed, too)

Answer 3

As Dave M. and tvanfosson said, you want to rewrite it as

catch (UnauthorizedAccessException) {}

The bigger question that should be asked, however, is why you are catching an exception on ignoring it (commonly called swallowing the exception)? This is generally a bad idea as it can (and usually does) hide problems in the application at runtime that can lead to very strange results and a difficult time debugging them.

Answer 4

Even though I'm a Java developer (not C#), @Scott Dorman is absolutely right. Why are you "swallowing the exception"? Better yet, what could throw the UnauthorizedAccessException? Here are common-sense possibilities:

1. The file doesn't exist
2. The directory doesn't exist
3. The current thread of control does not have the correct security privileges. In the *nix world, the current thread may be in the wrong group or the wrong user.
4. The disk crashed
5. The file's ACL is set to write only but not read. Likewise, for the directory.

The above of course is an incomplete list.

Answer 5

Assuming the comment in your original code is an accurate description of what you're trying to do, I think you want to write it like this:

foreach (FileInfo fi in di.GetFiles())
{
    //TODO:  what exceptions should be handled here?
    collection.Add(fi.Name);
}

// populate collection for each directory we have authorized access to
foreach (DirectoryInfo d in di.GetDirectories())
{
    try
    {
        populateItems(collection, d);
    }
    catch (UnauthorizedAccessException)
    {
        //ignore and move onto next directory
    }
}

And then you need to work on that TODO item.

Answer 6

I agree with the people who say it's probably a bad idea to simply ignore the exception. If you're not going to re-throw it then at the very least log it somewhere. I've written small tools that process a list of files where I didn't want errors on individual files to crash the whole program, and in such cases I would print a warning message so I could see which files were skipped.

The only time I personally ever catch an exception without naming it, as in catch(xxxException), is if I'm going to react to it in some way and then re-throw it so that I can catch it in some outer routine. E.g.:

try
{
    // do something
    // ...
}
catch(UnauthorizedAccessException)
{
    // react to this exception in some way
    // ...

    // let _someone_ know the exception happened
    throw;
}