在C#中，内存流（MemoryStream）默认是不可扩展的，即在写入大量数据时可能会导致内存不足的问题。解决这个问题的一种方法是使用可扩展内存流（ExpandableMemoryStream），它是一个自定义的内存流类，可以根据需要动态扩展内存大小。
下面是一个简单的可扩展内存流的示例代码：
public class ExpandableMemoryStream : Stream { private byte[] buffer; private int position; private int length; public ExpandableMemoryStream() { buffer = new byte[4096]; // 初始大小为4KB position = 0; length = 0; } public override bool CanRead => true; public override bool CanSeek => true; public override bool CanWrite => true; public override long Length => length; public override long Position { get => position; set => position = (int)value; } public override void Flush() { // 无需实现 } public override int Read(byte[] buffer, int offset, int count) { int bytesRead = Math.Min(count, length - position); Array.Copy(this.buffer, position, buffer, offset, bytesRead); position += bytesRead; return bytesRead; } public override long Seek(long offset, SeekOrigin origin) { switch (origin) { case SeekOrigin.Begin: position = (int)offset; break; case SeekOrigin.Current: position += (int)offset; break; case SeekOrigin.End: position = length - (int)offset; break; } return position; } public override void SetLength(long value) { if (value <= length) { length = (int)value; if (position > length) position = length; } else { int newSize = (int)value; byte[] newBuffer = new byte[newSize]; Array.Copy(buffer, newBuffer, length); buffer = newBuffer; length = newSize; } } public override void Write(byte[] buffer, int offset, int count) { int newPosition = position + count; if (newPosition > this.buffer.Length) { int newSize = Math.Max(newPosition, this.buffer.Length * 2); byte[] newBuffer = new byte[newSize]; Array.Copy(this.buffer, newBuffer, position); this.buffer = newBuffer; } Array.Copy(buffer, offset, this.buffer, position, count); position = newPosition; length = Math.Max(position, length); } } 使用可扩展内存流时，可以像使用内存流一样进行读写操作，但不用担心内存不足的问题。当写入的数据量超过当前内存大小时，可扩展内存流会自动扩展内存大小，以适应更多的数据。
ExpandableMemoryStream stream = new ExpandableMemoryStream(); byte[] data = new byte[8192]; // 假设有8KB数据需要写入 stream.Write(data, 0, data.Length); // 读取数据 byte[] buffer = new byte[4096]; int bytesRead = stream.Read(buffer, 0, buffer.Length); 这样，就能够解决C#内存流不可扩展的问题。
