FileStream.CanWrite 属性

定义

命名空间:

System.IO

程序集:

System.Runtime.dll

Source:

FileStream.cs

获取一个值，该值指示当前流是否支持写入。

public:
 virtual property bool CanWrite { bool get(); };

public override bool CanWrite { get; }

member this.CanWrite : bool

Public Overrides ReadOnly Property CanWrite As Boolean

属性值

Boolean

如果流支持写入，则为 true；如果流已关闭或是通过只读访问方式打开的，则为 false。

示例

以下示例使用 CanWrite 属性检查流是否支持写入。

using namespace System;
using namespace System::IO;
using namespace System::Text;

int main()
{
   String^ path = "c:\\temp\\MyTest.txt";
   
   // Ensure that the file is readonly.
   File::SetAttributes( path, static_cast<FileAttributes>(File::GetAttributes( path ) | FileAttributes::ReadOnly) );
   
   //Create the file.
   FileStream^ fs = gcnew FileStream( path,FileMode::OpenOrCreate,FileAccess::Read );
   try
   {
      if ( fs->CanWrite )
      {
         Console::WriteLine( "The stream for file {0} is writable.", path );
      }
      else
      {
         Console::WriteLine( "The stream for file {0} is not writable.", path );
      }
   }
   finally
   {
      if ( fs )
         delete (IDisposable^)fs;
   }
}

using System;
using System.IO;
using System.Text;

class Test
{
    
    public static void Main()
    {
        string path = @"c:\temp\MyTest.txt";

        // Ensure that the file is readonly.
        File.SetAttributes(path, File.GetAttributes(path) | FileAttributes.ReadOnly);

        //Create the file.
        using (FileStream fs = new FileStream (path, FileMode.OpenOrCreate, FileAccess.Read))
        {
            if (fs.CanWrite)
            {
                Console.WriteLine("The stream for file {0} is writable.", path);
            }
            else
            {
                Console.WriteLine("The stream for file {0} is not writable.", path);
            }
        }
    }
}

open System.IO

let path = @"c:\temp\MyTest.txt"

// Ensure that the file is readonly.
File.SetAttributes(path, File.GetAttributes path ||| FileAttributes.ReadOnly)

//Create the file.
do
    use fs = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Read)

    if fs.CanWrite then
        printfn $"The stream for file {path} is writable."

    else
        printfn $"The stream for file {path} is not writable."

Imports System.IO

Public Class Test

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

        'Ensure that the file is readonly.
        File.SetAttributes(path, File.GetAttributes(path) Or FileAttributes.ReadOnly)

        'Create the file.
        Dim fs As FileStream = New FileStream(path, FileMode.OpenOrCreate, FileAccess.Read)

        If fs.CanWrite Then
            Console.WriteLine("The stream connected to {0} is writable.", path)
        Else
            Console.WriteLine("The stream connected to {0} is not writable.", path)
        End If
        fs.Close()
    End Sub
End Class

下面是使用 CanWrite 属性的示例。 此代码的输出为“MyFile.txt 可写”。若要获取输出消息“MyFile.txt 可以写入和读取”。，请将 FileAccess 构造函数中的 FileStream 参数更改为 ReadWrite 。

using namespace System;
using namespace System::IO;
int main( void )
{
   FileStream^ fs = gcnew FileStream( "MyFile.txt",FileMode::OpenOrCreate,FileAccess::Write );
   if ( fs->CanRead && fs->CanWrite )
   {
      Console::WriteLine( "MyFile.txt can be both written to and read from." );
   }
   else
   {
      Console::WriteLine( "MyFile.txt is writable." );
   }

   return 0;
}

using System;
using System.IO;

class TestRW
{
    public static void Main(String[] args)
    {
        FileStream fs = new FileStream("MyFile.txt", FileMode.OpenOrCreate, FileAccess.Write);
        if (fs.CanRead && fs.CanWrite)
        {
            Console.WriteLine("MyFile.txt can be both written to and read from.");
        }
        else if (fs.CanWrite)
        {
            Console.WriteLine("MyFile.txt is writable.");
        }
    }
}

open System.IO

let fs = new FileStream("MyFile.txt", FileMode.OpenOrCreate, FileAccess.Write)

if fs.CanRead && fs.CanWrite then
    printfn "MyFile.txt can be both written to and read from."
elif fs.CanWrite then
    printfn "MyFile.txt is writable."

Imports System.IO

Class TestRW
    Public Shared Sub Main()
        Dim fs As New FileStream("MyFile.txt", FileMode.OpenOrCreate, FileAccess.Write)

        If fs.CanRead And fs.CanWrite Then
            Console.WriteLine("MyFile.txt can be both written to and read from.")
        ElseIf fs.CanWrite Then
            Console.WriteLine("MyFile.txt is writable.")
        End If
    End Sub
End Class

注解

如果派生自 Stream 的类不支持写入，则对 SetLength、 Write、 BeginWrite或 WriteByte 的调用将 NotSupportedException引发 。

如果流关闭，则此属性返回 false。

另请参阅

• 文件和流 I/O
• 如何：从文件中读取文本
• 如何：将文本写入文件