BinaryReader.ReadBytes(Int32) Metodo

Definizione

Spazio dei nomi:

System.IO

Assembly:

System.Runtime.dll

Origine:

BinaryReader.cs

Legge il numero specificato di byte dal flusso corrente in una matrice di byte e sposta in avanti la posizione corrente in base a tale numero di byte.

public:
 virtual cli::array <System::Byte> ^ ReadBytes(int count);

public virtual byte[] ReadBytes (int count);

abstract member ReadBytes : int -> byte[]
override this.ReadBytes : int -> byte[]

Public Overridable Function ReadBytes (count As Integer) As Byte()

Parametri

count

Int32

Numero di byte da leggere. Questo valore deve essere 0 o un numero non negativo; in caso contrario, si verificherà un'eccezione.

Restituisce

Byte[]

Matrice di byte contenente dati letti dal flusso sottostante. Può essere minore del numero di byte necessari se viene raggiunta la fine del flusso.

Eccezioni

ArgumentException

Il numero dei caratteri decodificati da leggere è maggiore di count. Questa situazione può verificarsi se un decodificatore Unicode restituisce caratteri di fallback o una coppia di surrogati.

IOException

Si è verificato un errore di I/O.

ObjectDisposedException

Il flusso è chiuso.

ArgumentOutOfRangeException

count è negativo.

Esempio

Nell'esempio di codice seguente viene illustrato come scrivere dati binari usando la memoria come archivio di backup e quindi verificare che i dati siano stati scritti correttamente.

using namespace System;
using namespace System::IO;
int main()
{
   const int arrayLength = 1000;
   
   // Create random data to write to the stream.
   array<Byte>^dataArray = gcnew array<Byte>(arrayLength);
   (gcnew Random)->NextBytes( dataArray );
   BinaryWriter^ binWriter = gcnew BinaryWriter( gcnew MemoryStream );
   
   // Write the data to the stream.
   Console::WriteLine(  "Writing the data." );
   binWriter->Write( dataArray );
   
   // Create the reader using the stream from the writer.
   BinaryReader^ binReader = gcnew BinaryReader( binWriter->BaseStream );
   
   // Set the stream position to the beginning of the stream.
   binReader->BaseStream->Position = 0;
   
   // Read and verify the data.
   array<Byte>^verifyArray = binReader->ReadBytes( arrayLength );
   if ( verifyArray->Length != arrayLength )
   {
      Console::WriteLine( "Error writing the data." );
      return  -1;
   }

   for ( int i = 0; i < arrayLength; i++ )
   {
      if ( verifyArray[ i ] != dataArray[ i ] )
      {
         Console::WriteLine( "Error writing the data." );
         return  -1;
      }

   }
   Console::WriteLine( "The data was written and verified." );
}

using System;
using System.IO;

class BinaryRW
{
    static void Main()
    {
        const int arrayLength = 1000;

        // Create random data to write to the stream.
        byte[] dataArray = new byte[arrayLength];
        new Random().NextBytes(dataArray);

        BinaryWriter binWriter = new BinaryWriter(new MemoryStream());

        // Write the data to the stream.
        Console.WriteLine("Writing the data.");
        binWriter.Write(dataArray);

        // Create the reader using the stream from the writer.
        BinaryReader binReader =
            new BinaryReader(binWriter.BaseStream);

        // Set Position to the beginning of the stream.
        binReader.BaseStream.Position = 0;

        // Read and verify the data.
        byte[] verifyArray = binReader.ReadBytes(arrayLength);
        if(verifyArray.Length != arrayLength)
        {
            Console.WriteLine("Error writing the data.");
            return;
        }
        for(int i = 0; i < arrayLength; i++)
        {
            if(verifyArray[i] != dataArray[i])
            {
                Console.WriteLine("Error writing the data.");
                return;
            }
        }
        Console.WriteLine("The data was written and verified.");
    }
}

open System
open System.IO

let arrayLength = 1000

// Create random data to write to the stream.
let dataArray = Array.zeroCreate<byte> arrayLength
Random().NextBytes dataArray

let binWriter = new BinaryWriter(new MemoryStream())

// Write the data to the stream.ch
printfn "Writing the data."
binWriter.Write dataArray

// Create the reader using the stream from the writer.
let binReader = new BinaryReader(binWriter.BaseStream)

// Set Position to the beginning of the stream.
binReader.BaseStream.Position <- 0

// Read and verify the data.
let verifyArray = binReader.ReadBytes arrayLength
if verifyArray.Length <> arrayLength then
    printfn "Error writing the data."
else
    let mutable failed = false
    for i = 0 to arrayLength - 1 do
        if verifyArray[i] <> dataArray[i] then
            printfn "Error writing the data."
            failed <- true
    if not failed then
        printfn "The data was written and verified."

Imports System.IO

Public Class BinaryRW

    Shared Sub Main()
    
        Const upperBound As Integer = 1000

        ' Create random data to write to the stream.
        Dim dataArray(upperBound) As Byte
        Dim randomGenerator As New Random
        randomGenerator.NextBytes(dataArray)

        Dim binWriter As New BinaryWriter(New MemoryStream())

        ' Write the data to the stream.
        Console.WriteLine("Writing the data.")
        binWriter.Write(dataArray)

        ' Create the reader using the stream from the writer.
        Dim binReader As New BinaryReader(binWriter.BaseStream)

        ' Set the stream position to the beginning of the stream.
        binReader.BaseStream.Position = 0

        ' Read and verify the data.
        Dim verifyArray() As Byte = _
            binReader.ReadBytes(dataArray.Length)
        If verifyArray.Length <> dataArray.Length Then
            Console.WriteLine("Error writing the data.")
            Return
        End If
        For i As Integer = 0 To upperBound
            If verifyArray(i) <> dataArray(i) Then
                Console.WriteLine("Error writing the data.")
                Return
            End If
        Next i
        Console.WriteLine("The data was written and verified.")
    
    End Sub
End Class

Questo esempio legge il contenuto di un file e lo visualizza nella console come testo di dump. La fine del file letto viene rilevata quando la lunghezza della Byte matrice restituita da ReadBytes è zero.

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

public class DumpFileSample
{
    private static readonly int CHUNK_SIZE = 1024;
    public static void Main(String[] args)
    {
        if ((args.Length == 0) || !File.Exists(args[0]))
        {
            Console.WriteLine("Please provide an existing file name.");
        }
        else
        {
            using (FileStream fs = new FileStream(args[0], FileMode.Open, FileAccess.Read))
            {
                using (BinaryReader br = new BinaryReader(fs, new ASCIIEncoding()))
                {
                    byte[] chunk;

                    chunk = br.ReadBytes(CHUNK_SIZE);
                    while(chunk.Length > 0)
                    {
                        DumpBytes(chunk, chunk.Length);
                        chunk = br.ReadBytes(CHUNK_SIZE);
                    }
                }
            }
        }
    }

    public static void DumpBytes(byte[] bdata, int len)
    {
        int i;
        int j = 0;
        char dchar;
        // 3 * 16 chars for hex display, 16 chars for text and 8 chars
        // for the 'gutter' int the middle.
        StringBuilder dumptext = new StringBuilder("        ", 16 * 4 + 8);
        for (i = 0; i < len; i++)
        {
            dumptext.Insert(j * 3, String.Format("{0:X2} ", (int)bdata[i]));
            dchar = (char)bdata[i];
            //' replace 'non-printable' chars with a '.'.
            if (Char.IsWhiteSpace(dchar) || Char.IsControl(dchar))
            {
                dchar = '.';
            }
            dumptext.Append(dchar);
            j++;
            if (j == 16)
            {
                Console.WriteLine(dumptext);
                dumptext.Length = 0;
                dumptext.Append("        ");
                j = 0;
            }
        }
        // display the remaining line
        if (j > 0)
        {
            for (i = j; i < 16; i++)
            {
                dumptext.Insert(j * 3, "   ");
            }
            Console.WriteLine(dumptext);
        }
    }
}

open System
open System.IO
open System.Text

let CHUNK_SIZE = 1024

let dumpBytes (bdata: byte[]) len =
    let mutable j = 0
    // 3 * 16 chars for hex display, 16 chars for text and 8 chars
    // for the 'gutter' int the middle.
    let dumptext = StringBuilder("        ", 16 * 4 + 8)
    for i = 0 to len - 1 do
        dumptext.Insert(j * 3, $"{int bdata[i]:X2} ") |> ignore
        let dchar = char bdata[i]
        //' replace 'non-printable' chars with a '.'.
        let dchar = 
            if Char.IsWhiteSpace dchar || Char.IsControl dchar then
                '.'
            else 
                dchar
        dumptext.Append dchar |> ignore
        j <- j + 1
        if j = 16 then
            printfn $"{dumptext}"
            dumptext.Length <- 0
            dumptext.Append "        " |> ignore
            j <- 0
    // display the remaining line
    if j > 0 then
        for i = j to 15 do
            dumptext.Insert(j * 3, "   ") |> ignore
        printfn $"{dumptext}"

[<EntryPoint>]
let main args =
    if args.Length = 0 || File.Exists args[0] |> not then
        printfn "Please provide an existing file name."
    else
        use fs = new FileStream(args[0], FileMode.Open, FileAccess.Read)
        use br = new BinaryReader(fs, ASCIIEncoding())
        
        let mutable chunk = br.ReadBytes CHUNK_SIZE
        while chunk.Length > 0 do
            dumpBytes chunk chunk.Length
            chunk <- br.ReadBytes CHUNK_SIZE
    0

Imports System.IO
Imports System.Text

Module Module1
    Private ReadOnly CHUNK_SIZE As Integer = 1024
    Public Sub Main(args() As String)
        If ((args.Length = 0) OrElse Not File.Exists(args(0))) Then
            Console.WriteLine("Please provide an existing file name.")
        Else
            Using fs As FileStream = New FileStream(args(0), FileMode.Open, FileAccess.Read)
                Using br As New BinaryReader(fs, New ASCIIEncoding())
                    Dim chunk(CHUNK_SIZE) As Byte
                    chunk = br.ReadBytes(CHUNK_SIZE)

                    While chunk.Length > 0
                        DumpBytes(chunk, chunk.Length)
                        chunk = br.ReadBytes(CHUNK_SIZE)
                    End While
                End Using
            End Using
        End If
    End Sub

    Public Sub DumpBytes(bdata() As Byte, len As Integer)
        Dim i As Integer
        Dim j As Integer = 0
        Dim dchar As Char
        ' 3 * 16 chars for hex display, 16 chars for text and 8 chars
        ' for the 'gutter' int the middle.
        Dim dumptext As New StringBuilder("        ", 16 * 4 + 8)
        For i = 0 To len - 1
            dumptext.Insert(j * 3, String.Format("{0:X2} ", CType(bdata(i), Integer)))
            dchar = Convert.ToChar(bdata(i))
            ' replace 'non-printable' chars with a '.'.
            If Char.IsWhiteSpace(dchar) Or Char.IsControl(dchar) Then
                dchar = "."
            End If
            dumptext.Append(dchar)
            j += 1
            If j = 16 Then
                Console.WriteLine(dumptext)
                dumptext.Length = 0
                dumptext.Append("        ")
                j = 0
            End If
        Next i
        ' display the remaining line
        If j > 0 Then
            ' add blank hex spots to align the 'gutter'.
            For i = j To 15
                dumptext.Insert(j * 3, "   ")
            Next i
            Console.WriteLine(dumptext)
        End If
    End Sub

End Module

Commenti

BinaryReader non ripristina la posizione del file dopo un'operazione di lettura non riuscita.

Per un elenco di attività di I/O comuni, vedere Attività di I/O comuni.

Vedi anche

• File e Stream I/O
• Procedura: Leggere testo da un file
• Procedura: Scrivere un testo in un file