无法正确将 FileStream 读入 byte[]

Question

我有一些 C# 代码要调用为 TF(true,"C:\input.txt","C:\noexistsyet.file")，但是当我运行它时，它会在 FileStream.Read() 上中断，因为它会将文件的最后一块读入缓冲区，得到一个索引越界 @987654323 @。

对我来说，代码似乎合乎逻辑，尝试写入缓冲区时没有溢出。我以为我已经用rdlen 和_chunk 进行了所有设置，但也许我看错了。有什么帮助吗？

我的错误：ArgumentException was unhandled: Offset and length were out of bounds for the array or count is greater than the number of elements from index to the end of the source collection.

public static bool TF(bool tf, string filepath, string output)
    {
        long _chunk = 16 * 1024; //buffer count
        long total_size = 0
        long rdlen = 0;
        long wrlen = 0;
        long full_chunks = 0;
        long end_remain_buf_len = 0;
        FileInfo fi = new FileInfo(filepath);
        total_size = fi.Length;
        full_chunks = total_size / _chunk;
        end_remain_buf_len = total_size % _chunk;
        fi = null;
        FileStream fs = new FileStream(filepath, FileMode.Open);
        FileStream fw = new FileStream(output, FileMode.Create);
        for (long chunk_pass = 0; chunk_pass < full_chunks; chunk_pass++)
        {
            int chunk = (int)_chunk * ((tf) ? (1 / 3) : 3); //buffer count for xbuffer
            byte[] buffer = new byte[_chunk];
            byte[] xbuffer = new byte[(buffer.Length * ((tf) ? (1 / 3) : 3))];
            //Read chunk of file into buffer
            fs.Read(buffer, (int)rdlen, (int)_chunk); //ERROR occurs here
            //xbuffer = do stuff to make it *3 longer or *(1/3) shorter;
            //Write xbuffer into chunk of completed file
            fw.Write(xbuffer, (int)wrlen, chunk);
            //Keep track of location in file, for index/offset
            rdlen += _chunk;
            wrlen += chunk;
        }
        if (end_remain_buf_len > 0)
        {
                byte[] buffer = new byte[end_remain_buf_len];
                byte[] xbuffer = new byte[(buffer.Length * ((tf) ? (1 / 3) : 3))];
                fs.Read(buffer, (int)rdlen, (int)end_remain_buf_len); //error here too
                //xbuffer = do stuff to make it *3 longer or *(1/3) shorter;
                fw.Write(xbuffer, (int)wrlen, (int)end_remain_buf_len * ((tf) ? (1 / 3) : 3));
                rdlen += end_remain_buf_len;
                wrlen += chunk;
        }
        //Close opened files
        fs.Close();
        fw.Close();
        return false; //no functionality yet lol
    }

Answer 1

Stream（FileStream 的基类）的Read() 方法返回一个int，表示读取的字节数，0 表示没有更多字节要读取，所以你甚至不用需要事先知道文件大小：

public static void CopyFileChunked(int chunkSize, string filepath, string output)
{
    byte[] chunk = new byte[chunkSize];

    using (FileStream reader = new FileStream(filepath, FileMode.Open))
    using (FileStream writer = new FileStream(output, FileMode.Create))
    {
        int bytes;
        while ((bytes = reader.Read(chunk , 0, chunkSize)) > 0)
        {
            writer.Write(chunk, 0, bytes);
        }
    }
}

甚至File.Copy() 也可以解决问题，如果您可以让框架决定块大小。

Answer 2

我认为它在这条线上失败了：

  fw.Write(xbuffer, (int)wrlen, chunk);

您将 xbuffer 声明为

 byte[] xbuffer = new byte[(buffer.Length * ((tf) ? (1 / 3) : 3))];

由于1 / 3 是一个整数除法，它返回0。并且您声明xbuffer 的大小为0，因此错误。您可以通过将操作数之一转换为浮点类型或使用文字来修复它。但是你仍然需要将结果转换回整数。

 byte[] xbuffer = new byte[(int)(buffer.Length * ((tf) ? (1m / 3) : 3))];

chunk 声明中也存在同样的问题。