Como: abrir e anexar a um arquivo de logHow to: Open and append to a log file

StreamWriter e StreamReader gravam caracteres e leem caracteres de fluxos.StreamWriter and StreamReader write characters to and read characters from streams. O exemplo de código a seguir abre o arquivo log.txt para a entrada ou cria o arquivo caso ele ainda não exista e acrescenta informações de log ao final do arquivo.The following code example opens the log.txt file for input, or creates it if it doesn't exist, and appends log information to the end of the file. Em seguida, o exemplo grava o conteúdo do arquivo na saída padrão para exibição.The example then writes the contents of the file to standard output for display.

Como alternativa para esse exemplo, você pode armazenar as informações como uma única cadeia de caracteres ou uma matriz de cadeia de caracteres e usar o método File.WriteAllText ou File.WriteAllLines para obter a mesma funcionalidade.As an alternative to this example, you could store the information as a single string or string array, and use the File.WriteAllText or File.WriteAllLines method to achieve the same functionality.

Observação

Os usuários do Visual Basic podem optar por usar os métodos e propriedades fornecidas pela classe Log ou pela classe FileSystem para criar ou gravar em arquivos de log.Visual Basic users may choose to use the methods and properties provided by the Log class or FileSystem class for creating or writing to log files.

ExemploExample

using System;
using System.IO;

class DirAppend
{
    public static void Main()
    {
        using (StreamWriter w = File.AppendText("log.txt"))
        {
            Log("Test1", w);
            Log("Test2", w);
        }

        using (StreamReader r = File.OpenText("log.txt"))
        {
            DumpLog(r);
        }
    }

    public static void Log(string logMessage, TextWriter w)
    {
        w.Write("\r\nLog Entry : ");
        w.WriteLine($"{DateTime.Now.ToLongTimeString()} {DateTime.Now.ToLongDateString()}");
        w.WriteLine("  :");
        w.WriteLine($"  :{logMessage}");
        w.WriteLine ("-------------------------------");
    }

    public static void DumpLog(StreamReader r)
    {
        string line;
        while ((line = r.ReadLine()) != null)
        {
            Console.WriteLine(line);
        }
    }
}
// The example creates a file named "log.txt" and writes the following lines to it,
// or appends them to the existing "log.txt" file:

// Log Entry : <current long time string> <current long date string>
//  :
//  :Test1
// -------------------------------

// Log Entry : <current long time string> <current long date string>
//  :
//  :Test2
// -------------------------------

// It then writes the contents of "log.txt" to the console.
Imports System.IO

Class DirAppend
    Public Shared Sub Main()
        Using w As StreamWriter = File.AppendText("log.txt")
            Log("Test1", w)
            Log("Test2", w)
        End Using

        Using r As StreamReader = File.OpenText("log.txt")
            DumpLog(r)
        End Using
    End Sub

    Public Shared Sub Log(logMessage As String, w As TextWriter)
        w.Write(vbCrLf + "Log Entry : ")
        w.WriteLine($"{DateTime.Now.ToLongTimeString()} {DateTime.Now.ToLongDateString()}")
        w.WriteLine("  :")
        w.WriteLine($"  :{logMessage}")
        w.WriteLine("-------------------------------")
    End Sub

    Public Shared Sub DumpLog(r As StreamReader)
        Dim line As String
        line = r.ReadLine()
        While Not (line Is Nothing)
            Console.WriteLine(line)
            line = r.ReadLine()
        End While
    End Sub
End Class

' The example creates a file named "log.txt" and writes the following lines to it,
' or appends them to the existing "log.txt" file:

' Log Entry : <current long time string> <current long date string>
'  :
'  :Test1
' -------------------------------

' Log Entry : <current long time string> <current long date string>
'  :
'  :Test2
' -------------------------------

' It then writes the contents of "log.txt" to the console.

Confira tambémSee also