即每次复制文件的一小段，以节省总内存开销。当然，本机复制也可以采用.NET内部的System.IO.File.Copy方法。
/// <summary>
/// 复制文件
/// </summary>
/// <param name="fromFile">要复制的文件</param>
/// <param name="toFile">要保存的位置</param>
/// <param name="lengthEachTime">每次复制的长度</param>
private void CopyFile(string fromFile, string toFile, int lengthEachTime)
{
FileStream fileToCopy = new FileStream(fromFile, FileMode.Open, FileAccess.Read);
FileStream copyToFile = new FileStream(toFile, FileMode.Append, FileAccess.Write);
int lengthToCopy;
if (lengthEachTime < fileToCopy.Length)//如果分段拷贝，即每次拷贝内容小于文件总长度
{
byte[] buffer = new byte[lengthEachTime];
int copied = 0;
while (copied <= ((int)fileToCopy.Length - lengthEachTime))//拷贝主体部分
{
lengthToCopy = fileToCopy.Read(buffer, 0, lengthEachTime);
fileToCopy.Flush();
copyToFile.Write(buffer, 0, lengthEachTime);
copyToFile.Flush();
copyToFile.Position = fileToCopy.Position;
copied += lengthToCopy;
}
int left = (int)fileToCopy.Length - copied;//拷贝剩余部分
lengthToCopy = fileToCopy.Read(buffer, 0, left);
fileToCopy.Flush();
copyToFile.Write(buffer, 0, left);
copyToFile.Flush();
}
else//如果整体拷贝，即每次拷贝内容大于文件总长度
{
byte[] buffer = new byte[fileToCopy.Length];
fileToCopy.Read(buffer,0,(int)fileToCopy.Length);
fileToCopy.Flush();
copyToFile.Write(buffer, 0, (int)fileToCopy.Length);
copyToFile.Flush();
}
fileToCopy.Close();
copyToFile.Close();
}