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Console.Error (Propiedad)


Obtiene el flujo de salida de error estándar.

Espacio de nombres:   System
Ensamblado:  mscorlib (en mscorlib.dll)

Public Shared ReadOnly Property Error As TextWriter

Valor de propiedad

Type: System.IO.TextWriter

Objeto TextWriter que representa el flujo de salida de error estándar.

This standard error stream is set to the console by default. It can be set to another stream with the M:System.Console.SetError(System.IO.TextWriter) method. After the standard error stream is redirected, it can be reacquired by calling the M:System.Console.OpenStandardError method.

In console applications whose informational output is often redirected to a file, the standard error stream available through the P:System.Console.Error property can be used to display information to the console even if output is redirected. The following example displays product tables for 10 numbers at a time starting with 1. After every set of 10 numbers, the P:System.Console.Error property is used to ask the user whether to display the next set. If the standard output is redirected to a file, the user is still asked whether the routine should generate the next set of products.

Module Example
   Public Sub Main()
      Dim increment As Integer = 0
      Dim exitFlag As Boolean = False

      Do While Not exitFlag
         If Console.IsOutputRedirected Then
            Console.Error.WriteLine("Generating multiples of numbers from {0} to {1}",
                                    increment + 1, increment + 10)
         End If
         Console.WriteLine("Generating multiples of numbers from {0} to {1}",
                           increment + 1, increment + 10)
         For ctr As Integer = increment + 1 To increment + 10
            Console.Write("Multiples of {0}: ", ctr)
            For ctr2 As Integer = 1 To 10
               Console.Write("{0}{1}", ctr * ctr2, If(ctr2 = 10, "", ", "))

         increment += 10
         Console.Error.Write("Display multiples of {0} through {1} (y/n)? ",
                             increment + 1, increment + 10)
         Dim response As Char = Console.ReadKey(True).KeyChar
         If Not Console.IsOutputRedirected Then
            Console.CursorTop = Console.CursorTop - 1
         End If
         If Char.ToUpperInvariant(response) = "N" Then exitFlag = True
   End Sub
End Module

The following example is a command line utility named ExpandTabs that replaces tab characters in a text file with four spaces, the value defined by the tabSize variable. It redirects the standard input and output streams to files, but uses the P:System.Console.Error property to write the standard error stream to the console. It can be launched from the command line by supplying the name of the file that contains tab characters and the name of the output file.

Imports System.IO

Public Class ExpandTabs
   Private Const tabSize As Integer = 4
   Private Const usageText As String = "Usage: EXPANDTABSEX inputfile.txt outputfile.txt"

   Public Shared Sub Main(args() As String)
      Dim writer As StreamWriter = Nothing

      If args.Length < 2 Then
         Exit Sub
      End If

         writer = New StreamWriter(args(1))
         Console.SetIn(New StreamReader(args(0)))
      Catch e As IOException
         Exit Sub
      End Try

      Dim i As Integer = Console.Read()
      While i <> -1 
         Dim c As Char = Convert.ToChar(i)
         If c = ControlChars.Tab Then
            Console.Write("".PadRight(tabSize, " "c))
         End If
         i = Console.Read()
      End While

      ' Reacquire the standard output stream so that a
      ' completion message can be displayed.
      Dim standardOutput As New StreamWriter(Console.OpenStandardOutput)
      standardOutput.AutoFlush = True
      Console.WriteLine("EXPANDTABSEX has completed the processing of {0}.", args(0))
   End Sub
End Class

The following example is a simple text file viewer that displays the contents of one or more text files to the console. If there are no command line arguments, or if any files passed as command line arguments do not exist, the example calls the M:System.Console.SetError(System.IO.TextWriter) method to redirect error information to a file, calls the M:System.Console.OpenStandardError method in the process of reacquiring the standard error stream, and indicates that error information was written to a file.

Imports System.IO

Module ViewTextFile
   Public Sub Main()
      Dim args() As String = Environment.GetCommandLineArgs()
      Dim errorOutput As String = ""
      ' Make sure that there is at least one command line argument.
      If args.Length <= 1 Then
         errorOutput += "You must include a filename on the command line." +
      End If

      For ctr As Integer = 1 To args.GetUpperBound(0)
         ' Check whether the file exists.
         If Not File.Exists(args(ctr)) Then
            errorOutput += String.Format("'{0}' does not exist.{1}",
                                         args(ctr), vbCrLf)
            ' Display the contents of the file.
            Dim sr As New StreamReader(args(ctr))
            Dim contents As String = sr.ReadToEnd()
            Console.WriteLine("***** Contents of file '{0}':{1}{1}",
                              args(ctr), vbCrLf)
            Console.WriteLine("*****{0}", vbCrLf)
         End If

      ' Check for error conditions.
      If Not String.IsNullOrEmpty(errorOutput) Then
         ' Write error information to a file.
         Console.SetError(New StreamWriter(".\ViewTextFile.Err.txt"))
         ' Reacquire the standard error stream.
         Dim standardError As New StreamWriter(Console.OpenStandardError())
         standardError.AutoFlush = True
         Console.Error.WriteLine("{0}Error information written to ViewTextFile.Err.txt",
      End If
   End Sub
End Module
' If the example is compiled and run with the following command line:
'     ViewTextFile file1.txt file2.txt
' and neither file1.txt nor file2.txt exist, it displays the
' following output:
'     Error information written to ViewTextFile.Err.txt
' and writes the following text to ViewFileText.Err.txt:
'     'file1.txt' does not exist.
'     'file2.txt' does not exist.

Note that the P:System.IO.StreamWriter.AutoFlush property is set to true before reacquiring the error stream. This ensures that output will be sent to the console immediately rather than buffered.

.NET Framework
Disponible desde 1.1
Disponible desde 2.0
Windows Phone Silverlight
Disponible desde 7.0
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