File.AppendText(String) 方法

定义

创建一个 StreamWriter,它将 UTF-8 编码文本追加到现有文件或新文件(如果指定文件不存在)。

public:
 static System::IO::StreamWriter ^ AppendText(System::String ^ path);
public static System.IO.StreamWriter AppendText (string path);
static member AppendText : string -> System.IO.StreamWriter
Public Shared Function AppendText (path As String) As StreamWriter

参数

path
String

要向其中追加内容的文件的路径。

返回

StreamWriter

一个流写入器,它将 UTF-8 编码文本追加到指定文件或新文件。

例外

调用方没有所要求的权限。

.NET Framework 和 .net Core 版本早于2.1: path 是一个长度为零的字符串,仅包含空格,或包含一个或多个无效字符。 你可以使用 GetInvalidPathChars() 方法查询无效字符。

pathnull

指定的路径和/或文件名超过了系统定义的最大长度。

指定的路径无效(例如,目录不存在或在未映射的驱动器上)。

path 的格式无效。

示例

下面的示例将文本追加到文件中。 如果文件不存在,则方法会创建一个新的文件。 但是, temp 在驱动器 C 上指定的目录必须存在,此示例才能成功完成。

using namespace System;
using namespace System::IO;

int main()
{
   String^ path = "c:\\temp\\MyTest.txt";
   
   // This text is added only once to the file.
   if (  !File::Exists( path ) )
   {
      // Create a file to write to.
      StreamWriter^ sw = File::CreateText( path );
      try
      {
         sw->WriteLine( "Hello" );
         sw->WriteLine( "And" );
         sw->WriteLine( "Welcome" );
      }
      finally
      {
         if ( sw )
            delete (IDisposable^)sw;
      }
   }
   
   // This text is always added, making the file longer over time
   // if it is not deleted.
   StreamWriter^ sw = File::AppendText( path );
   try
   {
      sw->WriteLine( "This" );
      sw->WriteLine( "is Extra" );
      sw->WriteLine( "Text" );
   }
   finally
   {
      if ( sw )
         delete (IDisposable^)sw;
   }
   
   // Open the file to read from.
   StreamReader^ sr = File::OpenText( path );
   try
   {
      String^ s = "";
      while ( s = sr->ReadLine() )
      {
         Console::WriteLine( s );
      }
   }
   finally
   {
      if ( sr )
         delete (IDisposable^)sr;
   }
}
using System;
using System.IO;

class Test
{
    public static void Main()
    {
        string path = @"c:\temp\MyTest.txt";
        // This text is added only once to the file.
        if (!File.Exists(path))
        {
            // Create a file to write to.
            using (StreamWriter sw = File.CreateText(path))
            {
                sw.WriteLine("Hello");
                sw.WriteLine("And");
                sw.WriteLine("Welcome");
            }	
        }

        // This text is always added, making the file longer over time
        // if it is not deleted.
        using (StreamWriter sw = File.AppendText(path))
        {
            sw.WriteLine("This");
            sw.WriteLine("is Extra");
            sw.WriteLine("Text");
        }	

        // Open the file to read from.
        using (StreamReader sr = File.OpenText(path))
        {
            string s = "";
            while ((s = sr.ReadLine()) != null)
            {
                Console.WriteLine(s);
            }
        }
    }
}
Imports System.IO

Public Class Test
  Public Shared Sub Main()
    Dim path As String = "c:\temp\MyTest.txt"

    ' This text is added only once to the file. 
    If Not File.Exists(path) Then
      ' Create a file to write to.
      Using sw As StreamWriter = File.CreateText(path)
        sw.WriteLine("Hello")
        sw.WriteLine("And")
        sw.WriteLine("Welcome")
      End Using
    End If

    ' This text is always added, making the file longer over time 
    ' if it is not deleted.
    Using sw As StreamWriter = File.AppendText(path)
      sw.WriteLine("This")
      sw.WriteLine("is Extra")
      sw.WriteLine("Text")
    End Using

    ' Open the file to read from. 
    Using sr As StreamReader = File.OpenText(path)
      Do While sr.Peek() >= 0
        Console.WriteLine(sr.ReadLine())
      Loop
    End Using

  End Sub
End Class

注解

此方法等效于 StreamWriter(String, Boolean) 构造函数重载。 如果指定的文件 path 不存在,则创建该文件。 如果文件存在,则将操作写入到 StreamWriter 文件中。 允许其他线程在文件打开时读取该文件。

path允许参数指定相对或绝对路径信息。 相对路径信息被解释为相对于当前工作目录。 若要获取当前工作目录,请参见 GetCurrentDirectory

path参数不区分大小写。

有关常见 i/o 任务的列表,请参阅 常见 I/o 任务

适用于

另请参阅