UnauthorizedAccessException

Your C# program has caused an UnauthorizedAccessException. What could cause this error and how could it be fixed? Learn how to handle this kind of exception safely.

This error can be caused by using a path that the operating system does not accept. For example, if we try to write to a system file that is part of the OS, this exception may occur.

Example

The statement in this code that uses StreamWriter is completely correct, but the underlying operating system does not allow modifications to the specified file path.

using System;
using System.IO;

class Program
{
    static void Main()
    {
        try
        {
            // Part 1: try to write a file at a path that cannot be written.
            using (StreamWriter writer = new StreamWriter(@"C:\Windows\notepad.exe"))
            {
            }
        }
        catch (UnauthorizedAccessException ex)
        {
            // Part 2: catch and print the error.
            Console.WriteLine(ex);
        }
    }
}
System.UnauthorizedAccessException: Access to the path 'C:\Windows\notepad.exe' is denied.
   at Microsoft.Win32.SafeHandles.SafeFileHandle.CreateFile...
   ...
   at Program.Main() in C:\Users\...\programs\consoletemp\Program.cs:line 11

Exception class

It is possible to catch UnauthorizedAccessException by just testing for Exception in a catch block. This is probably the easiest way to handle this error.

Summary

UnauthorizedAccessException is not a kind of IOException, but it can be handled by testing for the Exception base class. It indicates the OS does not allow writing to a file location.