StreamReader.Peek 方法

定义

命名空间:

System.IO

程序集:

System.Runtime.dll

Source:

StreamReader.cs

返回下一个可用字符，但不使用它。

public:
 override int Peek();

public override int Peek ();

override this.Peek : unit -> int

Public Overrides Function Peek () As Integer

返回

Int32

为表示下一个要读取的字符的整数，或者，如果没有要读取的字符或该流不支持查找，则为 -1。

例外

IOException

出现 I/O 错误。

示例

下面的代码示例从文件中读取行，直到到达文件的末尾。

using namespace System;
using namespace System::IO;

int main()
{
   String^ path = "c:\\temp\\MyTest.txt";
   try
   {
      if ( File::Exists( path ) )
      {
         File::Delete( path );
      }
      StreamWriter^ sw = gcnew StreamWriter( path );
      try
      {
         sw->WriteLine( "This" );
         sw->WriteLine( "is some text" );
         sw->WriteLine( "to test" );
         sw->WriteLine( "Reading" );
      }
      finally
      {
         delete sw;
      }

      StreamReader^ sr = gcnew StreamReader( path );
      try
      {
         while ( sr->Peek() > -1 )
         {
            Console::WriteLine( sr->ReadLine() );
         }
      }
      finally
      {
         delete sr;
      }
   }
   catch ( Exception^ e )
   {
      Console::WriteLine( "The process failed: {0}", e );
   }
}

using System;
using System.IO;

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

        try
        {
            if (File.Exists(path))
            {
                File.Delete(path);
            }

            using (StreamWriter sw = new StreamWriter(path))
            {
                sw.WriteLine("This");
                sw.WriteLine("is some text");
                sw.WriteLine("to test");
                sw.WriteLine("Reading");
            }

            using (StreamReader sr = new StreamReader(path))
            {

                while (sr.Peek() > -1)
                {
                    Console.WriteLine(sr.ReadLine());
                }
            }
        }
        catch (Exception e)
        {
            Console.WriteLine("The process failed: {0}", e.ToString());
        }
    }
}

Imports System.IO
Imports System.Text

Public Class Test

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

        Try
            If File.Exists(path) Then
                File.Delete(path)
            End If

            Dim sw As StreamWriter = New StreamWriter(path)
            sw.WriteLine("This")
            sw.WriteLine("is some text")
            sw.WriteLine("to test")
            sw.WriteLine("Reading")
            sw.Close()

            Dim sr As StreamReader = New StreamReader(path)

            Do While sr.Peek() > -1
                Console.WriteLine(sr.ReadLine())
            Loop
            sr.Close()
        Catch e As Exception
            Console.WriteLine("The process failed: {0}", e.ToString())
        End Try
    End Sub
End Class

注解

方法 Peek 返回一个整数值，以确定文件末尾是否发生了另一个错误。 这样，用户就可以先检查返回的值为 -1，然后再将其强制转换为Char类型。

此方法重写 TextReader.Peek。

对象的当前位置 StreamReader 不会由 Peek更改。

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