C# Signature:
[DllImport("kernel32.dll")]
static extern uint FormatMessage(uint dwFlags, IntPtr lpSource,
uint dwMessageId, uint dwLanguageId, [Out] StringBuilder lpBuffer,
uint nSize, IntPtr Arguments);
// the version, the sample is built upon:
[DllImport("Kernel32.dll", SetLastError=true)]
static extern uint FormatMessage( uint dwFlags, IntPtr lpSource,
uint dwMessageId, uint dwLanguageId, ref IntPtr lpBuffer,
uint nSize, IntPtr pArguments);
// the parameters can also be passed as a string array:
[DllImport("Kernel32.dll", SetLastError=true)]
static extern uint FormatMessage( uint dwFlags, IntPtr lpSource,
uint dwMessageId, uint dwLanguageId, ref IntPtr lpBuffer,
uint nSize, string[] Arguments);
// see the sample code
[DllImport("kernel32.dll", SetLastError = true)]
static extern uint FormatMessage(uint dwFlags, IntPtr lpSource, uint dwMessageId, uint dwLanguageId, [Out] StringBuilder lpBuffer, uint nSize, string[] Arguments);
VB.NET Signature:
<DllImport("Kernel32.dll", EntryPoint:="FormatMessageW", SetLastError:=True, CharSet:=CharSet.Unicode, CallingConvention:=CallingConvention.StdCall)> _
Public Shared Function FormatMessage(ByVal dwFlags As Integer, ByRef lpSource As IntPtr, ByVal dwMessageId As Integer, ByVal dwLanguageId As Integer, ByRef lpBuffer As [String], ByVal nSize As Integer, ByRef Arguments As IntPtr) As Integer
End Function
User-Defined Types:
None.
Notes:
To have FormatMessage substitute %1, %2, etc. with arguments you pass it, declare FormatMessage with a string[] for the last parameter and just pass a normal C# string array. You need to include FORMAT_MESSAGE_ARGUMENT_ARRAY in the dwFlags parameter for this to work.
Tips & Tricks:
If you are trying use FormatMessage to "decode" an error from Marshal.GetLastWin32Error, go take a look at Marshal.ThrowExceptionForHR (http://msdn.microsoft.com/en-us/library/ckxcyk36(v=VS.80).aspx).
Sample Code:
// from header files
const uint FORMAT_MESSAGE_ALLOCATE_BUFFER = 0x00000100;
const uint FORMAT_MESSAGE_IGNORE_INSERTS = 0x00000200;
const uint FORMAT_MESSAGE_FROM_SYSTEM = 0x00001000;
const uint FORMAT_MESSAGE_ARGUMENT_ARRAY = 0x00002000;
const uint FORMAT_MESSAGE_FROM_HMODULE = 0x00000800;
const uint FORMAT_MESSAGE_FROM_STRING = 0x00000400;
int nLastError= Marshal.GetLastWin32Error();
IntPtr lpMsgBuf= IntPtr.Zero;
uint dwChars= FormatMessage(
FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
IntPtr.Zero,
(uint)nLastError,
0, // Default language
ref lpMsgBuf,
0,
IntPtr.Zero);
if (dwChars==0)
{
// Handle the error.
int le= Marshal.GetLastWin32Error();
return null;
}
string sRet= Marshal.PtrToStringAnsi(lpMsgBuf);
// Free the buffer.
lpMsgBuf= LocalFree( lpMsgBuf );
return sRet;
// add for the forth signature
try
{
StringBuilder msgBuilder = new StringBuilder(101);
string formatExpression = "%1,%2%!";
string[] formatArgs = new string[] { "Hello", "world" };
IntPtr formatPtr = Marshal.StringToHGlobalAnsi(formatExpression);
//must specify the FORMAT_MESSAGE_ARGUMENT_ARRAY flag when pass an array
uint length = FormatMessage(FORMAT_MESSAGE_FROM_STRING | FORMAT_MESSAGE_ARGUMENT_ARRAY, formatPtr, 0, 0, msgBuilder, 101, formatArgs);
if (length == 0)
{
FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, IntPtr.Zero, (uint)Marshal.GetLastWin32Error(), 0, msgBuilder, 101, null);
Console.WriteLine("Error:" + msgBuilder.ToString());
}
else
{
Console.WriteLine("Format result:" + msgBuilder.ToString() + ", length:" + length.ToString());
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
Alternative Managed API:
This functionality is also given by System.ComponentModel.Win32Exception:
string errorMessage = new Win32Exception(Marshal.GetLastWin32Error()).Message;
Console.WriteLine(errorMessage);
Yet the sample might still be useful for messages not provided by the system.
