Getting the Windows System Error Code title/description from its hex number

Question

I'm messing around with some windows functions using p/invoke. Occasionally, I get an error code that is not ERROR_SUCCESS (such an odd name).

Is there a way to look these up within the program? Forexample, if I get error 1017. Can I tell the user

The system has attempted to load or restore a file into the registry, but the specified file is not in a registry file format. (ERROR_NOT_REGISTRY_FILE: 0x3F9)

Instead of

Error Code: 1017

Answer 1

You could take the defines from winerror.h at Rensselaer Polytechnic Institute, and put them into an Enum:

public enum Win32ErrorCode : long {      ERROR_SUCCESS = 0L,      NO_ERROR = 0L,      ERROR_INVALID_FUNCTION = 1L,      ERROR_FILE_NOT_FOUND = 2L,      ERROR_PATH_NOT_FOUND = 3L,      ERROR_TOO_MANY_OPEN_FILES = 4L,      ERROR_ACCESS_DENIED = 5L,      etc. } 

Then if your error code is in a variable error_code you would use :

Enum.GetName(typeof(Win32ErrorCode), error_code); 

Answer 2

I'm not sure if there's a niifty .NET wrapper, but you could call the FormatMessage API using P/Invoke.

See this answer for how it would normally be called from native code. Though the question refers to grabbing error codes from HRESULTs, the answer also applies for retreiving codes from the regular OS error codes coming from GetLastError/GetLastWin32Error).

EDIT: Thanks Malfist for pointing me to pinvoke.net, which includes alternative, managed API:

using System.ComponentModel;  string errorMessage = new Win32Exception(Marshal.GetLastWin32Error()).Message; Console.WriteLine(errorMessage);