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StreamReader.Read Method (Char[], Int32, Int32)

.NET Framework 3.5

Other Versions

Updated: December 2010

Reads a specified maximum number of characters from the current stream into a buffer, beginning at the specified index.

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

Syntax

C++

JScript

Copy

public override int Read(
	char[] buffer,
	int index,
	int count
)

Parameters

buffer: Type: System.Char[]
When this method returns, contains the specified character array with the values between index and (index + count - 1) replaced by the characters read from the current source.

index: Type: System.Int32
The index of buffer at which to begin writing.

count: Type: System.Int32
The maximum number of characters to read.

Return Value

Type: System.Int32
The number of characters that have been read, or 0 if at the end of the stream and no data was read. The number will be less than or equal to the count parameter, depending on whether the data is available within the stream.

Exceptions

Exception	Condition
ArgumentException	The buffer length minus index is less than count.
ArgumentNullException	buffer is null.
ArgumentOutOfRangeException	index or count is negative.
IOException	An I/O error occurs, such as the stream is closed.

Remarks

This method overrides Read.

This method returns an integer so that it can return 0 if the end of the stream has been reached.

When using the Read method, it is more efficient to use a buffer that is the same size as the internal buffer of the stream, where the internal buffer is set to your desired block size, and to always read less than the block size. If the size of the internal buffer was unspecified when the stream was constructed, its default size is 4 kilobytes (4096 bytes). If you manipulate the position of the underlying stream after reading data into the buffer, the position of the underlying stream might not match the position of the internal buffer. To reset the internal buffer, call the DiscardBufferedData method; however, this method slows performance and should be called only when absolutely necessary.

This method returns after either the number of characters specified by the count parameter are read, or the end of the file is reached. ReadBlock is a blocking version of Read.

For a list of common I/O tasks, see Common I/O Tasks.

Examples

The following code example reads five characters at a time until the end of the file is reached.

C++

Copy

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)) 
            {
                //This is an arbitrary size for this example.
                char[] c = null;

                while (sr.Peek() >= 0) 
                {
                    c = new char[5];
                    sr.Read(c, 0, c.Length);
                    //The output will look odd, because
                    //only five characters are read at a time.
                    Console.WriteLine(c);
                }
            }
        } 
        catch (Exception e) 
        {
            Console.WriteLine("The process failed: {0}", e.ToString());
        }
    }
}

Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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

Version Information