C# FileStream.Read 没有读取最后一个块

Question

我将二进制文件逐块读取为十六进制。

用FileStream.Read和File.ReadAllBytes

不一样

FileSteram.Read

int limit = 0;
if (openFileDlg.FileName.Length > 0)
{
    fileName = openFileDlg.FileName;
    FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read);
    fsLen = (int)fs.Length;
    int count = 0;
    limit = 100;
    byte[] read_buff = new byte[limit];
    StringBuilder sb = new StringBuilder();
    while ( (count = fs.Read(read_buff, 0, limit)) > 0)
    {
         foreach (byte b in read_buff)
         {
            sb.Append(Convert.ToString(b, 16).PadLeft(2, '0'));
         }

    }
    rtxb_bin.AppendText(sb.ToString() + "\n");
}

File.ReadAllBytes

if (openFileDlg.FileName.Length > 0)
{
        fileName = openFileDlg.FileName;
        byte[] fileBytes = File.ReadAllBytes(fileName);
        StringBuilder sb2 = new StringBuilder();

        foreach (byte b2 in fileBytes)
        {
            sb2.Append(Convert.ToString(b2, 16).PadLeft(2, '0'));
        }
        rtxb_allbin.AppendText(sb2.ToString());
 }

案例 1，结果是...

    ........04c0020f00452a00421346108129844f2138448500208020250405250043188510812e0

案例 2 是

      .......04c0020f00452a00421346108129844f2138448500208020250405250043188510812e044f212cc48120c24125404f2069c2c0008bff35f8f401efbd17047

FileStream.Read 在“12e0”之后没有读取缺少“44f212cc48120c24125404f2069c2c0008bff35f8f401efbd17047”

如何使用 FileStream.Read 读取所有字节？

为什么 FileStream.Read 不读取最后一个块？

Answer 1

您需要更新偏移量和计数。

Sintaxis

public override int Read(
    byte[] array,
    int offset,
    int count
)

Example

public static byte[] ReadFile(string filePath)
{
  byte[] buffer;
  FileStream fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read);
  try
  {
    int length = (int)fileStream.Length;  // get file length
    buffer = new byte[length];            // create buffer
    int count;                            // actual number of bytes read
    int sum = 0;                          // total number of bytes read

    // read until Read method returns 0 (end of the stream has been reached)
    while ((count = fileStream.Read(buffer, sum, length - sum)) > 0)
      sum += count;  // sum is a buffer offset for next reading
  }
  finally
  {
    fileStream.Close();
  }
  return buffer;
}

Reference

Answer 2

很可能您觉得它没有读取最后一个块。假设您有长度为 102 的文件。循环的第一次迭代读取前 100 个字节，一切都很好。但是第二个（最后一个）会发生什么？您将两个字节读入长度为 100 的 read_buff。现在缓冲区包含最后一个块的 2 个字节和前一个（第一个）块的 98 个字节，因为 Read 不会清除缓冲区。然后你继续：

 foreach (byte b in read_buff)
 {
    sb.Append(Convert.ToString(b, 16).PadLeft(2, '0'));
 }

结果，sb 第一个块有 100 个字节，最后一个块有 2 个字节，然后第一个块有 98 个字节。如果你不仔细看，它可能看起来只是跳过了最后一个块，而实际上它重复了前一个块的一部分。

要修复，请使用 count（表示实际读入缓冲区的字节数）仅适用于 read_buff:

的有效部分

for (int i = 0; i < count; i++) {
    sb.Append(Convert.ToString(read_buff[i], 16).PadLeft(2, '0'));
}

Answer 3

   public static void ReadAndProcessLargeFile(string theFilename, long whereToStartReading = 0)
    {
        FileInfo info = new FileInfo(theFilename);
        long fileLength = info.Length;
        long timesToRead = (fileLength / megabyte);
        long ctr = 0;
        long timesRead = 0;

        FileStream fileStram = new FileStream(theFilename, FileMode.Open, FileAccess.Read);
        using (fileStram)
        {
            byte[] buffer = new byte[megabyte];

            fileStram.Seek(whereToStartReading, SeekOrigin.Begin);

            int bytesRead = 0;
            
            //bytesRead = fileStram.Read(buffer, 0, megabyte);
            //ctr = ctr + 1;

            while ((bytesRead = fileStram.Read(buffer, 0, megabyte)) > 0)
            {
                ProcessChunk(buffer, bytesRead);
                buffer = new byte[megabyte]; // This solves last read prob
            }

        }
    }

    private static void ProcessChunk(byte[] buffer, int bytesRead)
    {
        // Do the processing here
        string utfString = Encoding.UTF8.GetString(buffer, 0, bytesRead);
        Console.Write(utfString);
    }

C# FileStream.Read 没有读取最后一个块

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