如何：打开并追加到日志文件
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.
