VB.如何设置最大字节写入流写入器与缓冲区

Question

我有一个流写入器，从一个文件读取并写入到另一个在中间的缓冲区…我使用fseek来查找字节位置，但是，它从字节位置写入到文件结束，我希望它从字节位置写入到x字节。我该如何指定呢?此外，文件可能很大，所以数学必须通过int64…下面是代码:

 Dim bytesRead As Integer
        Dim buffer(4096) As Byte
        Using inFile As New System.IO.FileStream("c:some pathfolderfile1.ext", IO.FileMode.Open, IO.FileAccess.Read)
  inFile.Seek(s, SeekOrigin.Current)
            Using outFile As New System.IO.FileStream("c:some pathfolderfile2.ext", IO.FileMode.Create, IO.FileAccess.Write)
                Do
                    bytesRead = inFile.Read(buffer, 0, buffer.Length)
                    If bytesRead > 0 Then
                        outFile.Write(buffer, 0, bytesRead)
                    End If
                Loop While bytesRead > 0
            End Using
        End Using

Answer 1

正如@Hans所说，您需要跟踪到目前为止已读取的字节总数，这是每次调用read()所返回的值;把它累加到一个变量里。您还需要考虑要读取的最后一个"块"，因为它可能小于缓冲区的大小。这个过程可能看起来像…

    Dim StartAt As Int64 = 2000
    Dim NumBytesToCopy As Int64 = 10000
    Dim TotalBytesCopied As Int64 = 0
    Dim bytesRead As Integer
    Dim buffer(4096) As Byte
    Using inFile As New System.IO.FileStream("c:some pathfolderfile1.ext", IO.FileMode.Open, IO.FileAccess.Read)
        inFile.Seek(StartAt, IO.SeekOrigin.Begin)
        Using outFile As New System.IO.FileStream("c:some pathfolderfile2.ext", IO.FileMode.Create, IO.FileAccess.Write)
            Do
                If NumBytesToCopy - TotalBytesCopied < buffer.Length Then
                    ReDim buffer(NumBytesToCopy - TotalBytesCopied)
                End If
                bytesRead = inFile.Read(buffer, 0, buffer.Length)
                If bytesRead > 0 Then
                    outFile.Write(buffer, 0, bytesRead)
                    TotalBytesCopied = TotalBytesCopied + bytesRead
                End If
            Loop While bytesRead > 0 AndAlso TotalBytesCopied < NumBytesToCopy
        End Using
    End Using