Question

如何在不将整个文件加载到内存中的情况下，逐段读取任意文件并逐个处理（意味着逐字节或其他一些可提供最佳读取性能的块大小）？处理的一个示例是生成文件的MD5哈希，尽管答案可以应用于任何操作。

我想拥有或写下这个，但如果我能获得现有的代码也很棒。

（C＃）

Answer 1

以下是如何在不将整个内容加载到内存中的情况下以1KB的块读取文件的示例：

const int chunkSize = 1024; // read the file by chunks of 1KB
using (var file = File.OpenRead("foo.dat"))
{
    int bytesRead;
    var buffer = new byte[chunkSize];
    while ((bytesRead = file.Read(buffer, 0, buffer.Length)) > 0)
    {
        // TODO: Process bytesRead number of bytes from the buffer
        // not the entire buffer as the size of the buffer is 1KB
        // whereas the actual number of bytes that are read are 
        // stored in the bytesRead integer.
    }
}

Answer 2

System.IO.FileStream未将文件加载到内存中此流是可搜索的，MD5哈希算法也不必加载流（文件）介绍内存。

请将file_path替换为您的文件路径。

byte[] hash = null;

using (var file = new FileStream(file_path, FileMode.Open))
{
    using (var md5 = new System.Security.Cryptography.MD5CryptoServiceProvider())
    {
        hash = md5.ComputeHash(stream);
    }
}

此处，您的MD5哈希将存储在hash变量中。

Answer 3

   int fullfilesize = 0;// full size of file
    int DefaultReadValue = 10485760; //read 10 mb at a time
    int toRead = 10485760;
    int position =0;

  //  int 
 //   byte[] ByteReadFirst = new byte[10485760];

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        using (var fs = new FileStream(@"filepath", FileMode.Open, FileAccess.Read))
        {
            using (MemoryStream requestStream = new MemoryStream())
            {


                fs.Position = position;

                if (fs.Position >= fullfilesize)
                {
                    MessageBox.Show(" all done");
                    return;
                }
                System.Diagnostics.Debug.WriteLine("file position" + fs.Position);

                if (fullfilesize-position < toRead)
                {
                    toRead = fullfilesize - position;
                    MessageBox.Show("last time");
                }
                System.Diagnostics.Debug.WriteLine("toread" + toRead);
                int    bytesRead;
                byte[] buffer = new byte[toRead];
                int offset = 0;
                position += toRead;
                while (toRead > 0 && (bytesRead = fs.Read(buffer, offset, toRead)) > 0)
                {
                    toRead -= bytesRead;
                    offset += bytesRead;
                }

                toRead = DefaultReadValue;


            }
        }
    }

复制Darin，此方法将读取10mb块直到文件末尾

Answer 4

const int MAX_BUFFER = 1024;
byte[] Buffer = new byte[MAX_BUFFER];
int BytesRead;
using (System.IO.FileStream fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read))
    while ((BytesRead = fileStream.Read(Buffer, 0, MAX_BUFFER)) != 0)
    {
        // Process this chunk starting from offset 0 
        // and continuing for bytesRead bytes!
    }

Answer 5

const long numberOfBytesToReadPerChunk = 1000;//1KB
using (BinaryReader fileData = new BinaryReader(File.OpenRead(aFullFilePath))
    while (fileData.BaseStream.Position - fileData.BaseStream.Length > 0)
        DoSomethingWithAChunkOfBytes(fileData.ReadBytes(numberOfBytesToReadPerChunk));

据我了解此处使用的功能（特别是BinaryReader.ReadBytes），无需跟踪您已阅读的字节数。您只需要知道while循环的长度和当前位置 - 流告诉您。

如何在不将整个文件加载到内存的情况下读取/流式传输文件？

5 个答案: