Read specific bytes of a file

Question

Is there any way to read specific bytes from a file?

For example, I have the following code to read all the bytes of the file:

byte[] test = File.ReadAllBytes(file);

I want to read the bytes from offset 50 to offset 60 and put them in an array.

Answer 1

Create a BinaryReader, read 10 bytes starting at byte 50:

byte[] test = new byte[10];
using (BinaryReader reader = new BinaryReader(new FileStream(file, FileMode.Open)))
{
    reader.BaseStream.Seek(50, SeekOrigin.Begin);
    reader.Read(test, 0, 10);
}

Answer 2

This should do it

var data = new byte[10];
int actualRead;

using (FileStream fs = new FileStream("c:\\MyFile.bin", FileMode.Open)) {
    fs.Position = 50;
    actualRead = 0;
    do {
        actualRead += fs.Read(data, actualRead, 10-actualRead);
    } while (actualRead != 10 && fs.Position < fs.Length);
}

Upon completion, data would contain 10 bytes between file's offset of 50 and 60, and actualRead would contain a number from 0 to 10, indicating how many bytes were actually read (this is of interest when the file has at least 50 but less than 60 bytes). If the file is less than 50 bytes, you will see EndOfStreamException .

Answer 3

LINQ版本：

byte[] test = File.ReadAllBytes(file).Skip(50).Take(10).ToArray();

Answer 4

You need to:

• seek to the data you want
• call Read repeatedly, checking the return value, until you have all the data you need

For example:

public static byte[] ReadBytes(string path, int offset, int count) {
    using(var file = File.OpenRead(path)) {
        file.Position = offset;
        offset = 0;
        byte[] buffer = new byte[count];
        int read;
        while(count > 0  &&  (read = file.Read(buffer, offset, count)) > 0 )
        {
            offset += read;
            count -= read;
        }
        if(count < 0) throw new EndOfStreamException();
        return buffer;     
    }
}

Answer 5

using System.IO;

public static byte[] ReadFile(string filePath)
{
    byte[] buffer;
    FileStream fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read);
    try
    {
        buffer = new byte[length];            // create buffer
        fileStream.Read(buffer, 50, 10);
     }
     finally
     {
         fileStream.Close();
     }
     return buffer;
 }

Answer 6

You can use filestream to and then call read

string pathSource = @"c:\tests\source.txt";

using (FileStream fsSource = new FileStream(pathSource,
    FileMode.Open, FileAccess.Read))
{

    // Read the source file into a byte array.
    byte[] bytes = new byte[fsSource.Length];
    int numBytesToRead = 10;
    int numBytesRead = 50;
    // Read may return anything from 0 to numBytesToRead.
    int n = fsSource.Read(bytes, numBytesRead, numBytesToRead);
}

Check this example MSDN

Answer 7

byte[] a = new byte[60];
byte[] b = new byte[10];
Array.Copy( a ,50, b , 0 , 10 );