File.AppendText(String) 方法
定义
重要
一些信息与预发行产品相关，相应产品在发行之前可能会进行重大修改。 对于此处提供的信息，Microsoft 不作任何明示或暗示的担保。
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.StreamWriterPublic 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
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 是零长度字符串，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。
path 为 null。
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
以下示例将文本追加到文件。 如果文件不存在， 方法将创建一个新文件。 但是，驱动器 C 上命名的 temp 目录必须存在，该示例才能成功完成。
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);
}
}
}
}
open System.IO
let path = @"c:\temp\MyTest.txt"
// This text is added only once to the file.
if File.Exists path |> not then
// Create a file to write to.
use 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.
do
use sw = File.AppendText path
sw.WriteLine "This"
sw.WriteLine "is Extra"
sw.WriteLine "Text"
// Open the file to read from.
do
use sr = File.OpenText path
let mutable s = sr.ReadLine()
while isNull s |> not do
printfn $"{s}"
s <- sr.ReadLine()
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 path 文件不存在，则创建该文件。 如果文件确实存在，则向 StreamWriter 文件追加文本写入操作。 允许其他线程在文件打开时读取该文件。
允许 path 参数指定相对路径信息或绝对路径信息。 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，请参阅 GetCurrentDirectory。
参数 path 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。
