StreamReader.Peek Method (System.IO)

Peek Method

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Microsoft Visual Studio 2005/.NET Framework 2.0

Other versions are also available for the following:

.NET Framework Class Library

StreamReader.Peek Method

Returns the next available character but does not consume it.

Namespace: System.IO
Assembly: mscorlib (in mscorlib.dll)

Syntax

Visual Basic (Declaration)

Public Overrides Function Peek As Integer

Visual Basic (Usage)

Dim instance As StreamReader
Dim returnValue As Integer

returnValue = instance.Peek

public override int Peek ()

C++

public:
virtual int Peek () override

public int Peek ()

JScript

public override function Peek () : int

Return Value

An integer representing the next character to be read, or -1 if no more characters are available or the stream does not support seeking.

Exceptions

Exception type	Condition
IOException	An I/O error occurs.

Remarks

The Peek method returns an integer value in order to determine whether the end of the file, or another error has occurred. This allows a user to first check if the returned value is -1 before casting it to a Char type.

This method overrides Peek.

The current position of the StreamReader object is not changed by Peek. The returned value is -1 if no more characters are currently available.

For an example of using this method, see the Example section. The following table lists examples of other typical or related I/O tasks.

To do this...	See the example in this topic...
Create a text file.	How to: Write Text to a File
Write to a text file.	How to: Write Text to a File
Read from a text file.	How to: Read Text from a File
Append text to a file.	How to: Open and Append to a Log File File.AppendText FileInfo.AppendText
Get the size of a file.	FileInfo.Length
Get the attributes of a file.	File.GetAttributes
Set the attributes of a file.	File.SetAttributes
Determine if a file exists.	File.Exists
Read from a binary file.	How to: Read and Write to a Newly Created Data File
Write to a binary file.	How to: Read and Write to a Newly Created Data File

Example

The following code example reads lines from a file until the end of the file is reached.

Visual Basic

Imports System
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() >= 0
                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

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

C++

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() >= 0 )
         {
            Console::WriteLine( sr->ReadLine() );
         }
      }
      finally
      {
         delete sr;
      }
   }
   catch ( Exception^ e ) 
   {
      Console::WriteLine( "The process failed: {0}", e );
   }
}

import System.*;
import System.IO.*;

class Test
{
    public static void main(String[] args)
    {
        String path = "c:\\temp\\MyTest.txt";

        try {
            if (File.Exists(path)) {
                File.Delete(path);
            }
            StreamWriter sw = new StreamWriter(path);
            try {
                sw.WriteLine("This");
                sw.WriteLine("is some text");
                sw.WriteLine("to test");
                sw.WriteLine("Reading");
            }
            finally {
                sw.Dispose();
            }
            StreamReader sr = new StreamReader(path);
            try {
                while (sr.Peek() >= 0) {
                    Console.WriteLine(sr.ReadLine());
                }
            }
            finally {
                sr.Dispose();
            }
        }
        catch (System.Exception e) {
            Console.WriteLine("The process failed: {0}", e.ToString());
        }
    } //main
} //Test

Platforms

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

Version Information

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

Reference

StreamReader Class
StreamReader Members
System.IO Namespace

Other Resources

File and Stream I/O
How to: Read Text from a File
How to: Write Text to a File