如何：打开并追加到日志文件

  • 项目

StreamWriter 和 StreamReader 对流执行字符写入和读取操作。 下面的代码示例打开 log.txt 文件以供输入，或创建该文件（如果尚无文件的话），并将日志信息追加到文件末尾。 然后，示例将文件内容写入标准输出以供显示。

作为此示例的替换方法，可以将信息存储为一个字符串或字符串数组，并使用 File.WriteAllText 或 File.WriteAllLines 方法实现相同的功能。

注意

Visual Basic 用户可以选择使用 Log 类或 FileSystem 类提供的方法和属性，以创建或写入日志文件。

示例

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.

请参阅