Question

下面的代码显示了用于检索二进制数据的MS帮助示例的一部分

// Read bytes into outByte[] and retain the number of bytes returned.
retval = reader.GetBytes(1, startIndex, outByte, 0, bufferSize);

// Continue while there are bytes beyond the size of the buffer.
while (retval == bufferSize)
{
  writer.Write(outByte);
  writer.Flush();

  // Reposition start index to end of last buffer and fill buffer.
  startIndex += bufferSize;
  retval = reader.GetBytes(1, startIndex, outByte, 0, bufferSize);
}

// Write the remaining buffer.
writer.Write(outByte, 0, (int)retval - 1);
writer.Flush();

当我使用它时，如果输入数据是bufferSize的精确倍数，则最后一次写入计算为-1并引发异常。我做错了什么或示例不正确？我可以在尝试最后一次写入之前测试剩余的数据，但是如果有一个首选的方式来做这个比示例提供的那样我都是耳朵。

由于

Answer 1

如果您正在寻找如何操作，请按以下方式提出建议：

using (var conn = new SqlConnection(myConnectionString))
{
    conn.Open();
    using (var comm = conn.CreateCommand())
    {
        comm.CommandText = "select somedata from Foo";
        using (var rdr = comm.ExecuteReader())
        {
            using (var fs = File.Create(@"C:\temp\myfile.bin"))
            {
                const int BUFFER_SIZE = 2048;
                var buffer = new byte[BUFFER_SIZE];
                long offset = 0L;

                while (rdr.Read())
                {
                    int count;
                    while ((count = (int)rdr.GetBytes(0, offset, buffer, 0, BUFFER_SIZE)) > 0)
                    {
                        fs.Write(buffer, 0, count);
                        offset += count;
                    }
                }
            }
        }
    }
}

MDSN页面上的示例充满了问题 - 我甚至不打算挽救它。

SQLDataReader.GetBytes示例的MS示例是否存在问题

1 个答案: