有没有办法用C#在C#中创建FileStream
?例如,如果我在偏移100处打开 SomeFile.bin ,Stream.Position
将等于0,但是读取&写入将被100偏移。
我正在为我的公司开发混合文件格式,它将机器可读的二进制数据与现代PC可读的OPC文件(本质上是使用System.IO.Packaging
创建的ZIP文件)相结合。出于性能原因,二进制数据必须出现在文件的顶部。我了解ZIP文件将允许此操作(例如自解压缩档案),但不幸的是内部ZipIOCentralDirectoryBlock
类是hard-coded to reject ZIP files where the first file header doesn't appear at offset 0。为了避免临时文件(因为文件可能大到3.99GB),我想欺骗ZipPackage
认为它处理文件的开头,而实际上它是&# 39;阅读&写在偏移处。
答案 0 :(得分:3)
不确定。这是装饰器模式的完美案例:
基本上你创建了一个
的类Stream
(您正在装饰的抽象类)然后覆盖所有方法和属性,将调用传递给修饰实例。如果方法或属性知道流的位置或长度,则根据需要应用适当的调整。
编辑注意: 看起来您需要装饰抽象流,如下所示(无法在不实际打开文件的情况下创建文件流实例)。
这是装饰器本身的[截断]示例:
class OffsetStreamDecorator : Stream
{
private readonly Stream instance ;
private readonly long offset ;
public static Stream Decorate( Stream instance )
{
if ( instance == null ) throw new ArgumentNullException("instance") ;
FileStream decorator= new OffsetStreamDecorator( instance ) ;
return decorator;
}
private OffsetStreamDecorator( FileStream instance )
{
this.instance = instance ;
this.offset = instance.Position ;
}
#region override methods and properties pertaining to the file position/length to transform the file positon using the instance's offset
public override long Length
{
get { return instance.Length - offset ; }
}
public override void SetLength( long value )
{
instance.SetLength( value + offset );
}
public override long Position
{
get { return instance.Position - this.offset ; }
set { instance.Position = value + this.offset ; }
}
// etc.
#endregion
#region override all other methods and properties as simple pass-through calls to the decorated instance.
public override IAsyncResult BeginRead( byte[] array , int offset , int numBytes , AsyncCallback userCallback , object stateObject )
{
return instance.BeginRead( array , offset , numBytes , userCallback , stateObject );
}
public override IAsyncResult BeginWrite( byte[] array , int offset , int numBytes , AsyncCallback userCallback , object stateObject )
{
return instance.BeginWrite( array , offset , numBytes , userCallback , stateObject );
}
// etc.
#endregion
}
用法非常简单,具体如下:
using ( Stream baseStream = new FileStream( @"c:\foo\bar\somefile.dat" , FileMode.Open , FileAccess.Read , FileShare.Read ) )
{
// establish your offset
baseStream.Seek( 100 , SeekOrigin.Begin ) ;
using ( Stream decoratedStream = OffsetStreamDecorator.Decorate( baseStream ) )
{
// now you have a stream that reports a false position and length
// which you should be able to use anywhere a Stream is accepted.
PassDecoratedStreamToSomethingExpectingAVanillaStream( decoratedStream ) ;
}
}
轻松! (所有涉及的样板除外)