读取随机访问文件 [英] Reading Random Access Files

问题描述

我正在使用VB2008.
我继承自VB6，一直在使用随机访问文件，这些文件对结构化数据使用起来非常简单.
所以我的代码如下:

I am using VB2008.
Inherited from VB6, I have been using random access files which are really simple to use with structured data.
So I have this code below:

Dim f As Integer = FreeFile(), m As s_MailingList
FileOpen(f, MailFile, OpenMode.Random, OpenAccess.ReadWrite,OpenShare.LockRead, Len(m))
MailK = CInt(LOF(f)) \ Len(m)
ReDim Mail(MailK)
For i as Integer = 0 To MailK
   FileGet(f, Mail(i), i + 1)
Next i
FileClose(f)

它运行完美，但是我想使用.NET方法，这也可以运行:

it works perfectly, but I wanted to use .NET methods and this also works:

Dim fs As New FileStream(MailFile, FileMode.Open)
Using sr As New BinaryReader(fs)
   Dim b() As Byte = sr.ReadBytes(416)
''     do work to get into structure
   sr.Close()
End Using

我检查了第一行，它是正确的.我需要编写循环等.因此，我似乎基于Microsoft代码尝试了此操作，因为它似乎更简单:

I checked the first line and it is correct. I need to write loop etc. So I tried this based on Microsoft code as it seems simpler:

Using Reader As New Microsoft.VisualBasic.FileIO.TextFieldParser(MailFile)
    Reader.TextFieldType = FileIO.FieldType.FixedWidth
    Reader.SetFieldWidths(1, 40, 40, 40, 40, 40, 40, 20, 20, 20, 20, 20, 60, 5, 4, 1, 2, 1, 1)
    Dim currentrow() As String
    While Not Reader.EndOfData
        Try
            currentrow = Reader.ReadFields()
        Catch ex As Microsoft.VisualBasic.FileIO.MalformedLineException
            MsgBox(ex.Message , "is not valid and will be skipped.")
        End Try
   End While
End Using

最后的代码无法读取该行. FieldWidths总计为416.

有任何想法吗?

The last code fails to read the line. The FieldWidths add up to 416.

Any ideas?

推荐答案

确定吗?
仅累加非零单位:1 + 5 + 4 + 1 + 2 + 1 +1.
你有16点吗?
因为我得到一个奇数...

Are you sure?
Add up just the non-zero units: 1 + 5 + 4 + 1 + 2 + 1 + 1.
Do you get 16?
Because I get an odd number...

我写了这似乎有用.

I wrote this which seems to work.

Public Class OpenRandomFiles
   Private fs As FileStream, sr As BinaryReader
   Friend Sub New(ByVal fPath As String)
      fs = New FileStream(fPath, FileMode.Open, FileAccess.Read, FileShare.Read)
      sr = New BinaryReader(fs)
   End Sub
   Friend Sub Dispose()
      sr.Close()
      fs.Dispose()
   End Sub
#Region " Properties "
   Private fCount As Integer
   Friend ReadOnly Property Count() As Integer
      Get
         Return fCount
      End Get
   End Property
   Private fStrings() As String
   Friend ReadOnly Property Strings() As String()
      Get
         Return fStrings
      End Get
   End Property
   Private fWidths(), wCount As Integer
   Friend WriteOnly Property Widths() As Integer()
      Set(ByVal value As Integer())
         fWidths = value
         wCount = UBound(fWidths)
         ReDim fStrings(wCount)
         Dim w As Integer = 0
         For i As Integer = 0 To wCount
            w += fWidths(i)
         Next
         fCount = CInt(fs.Length \ w - 1)
      End Set
   End Property
#End Region
   Friend Function ReadLine() As Boolean
      Try
         For i As Integer = 0 To wCount
            Dim b() As Byte = sr.ReadBytes(fWidths(i))
            fStrings(i) = ""
            For k as Integer = 0 To UBound(b)
               fStrings(i) = Chr(b(k))
            Next k
         Next
         Return False
      Catch ex As Exception
         Return True
      End Try
   End Function
End Class

像这样

It works like this

Dim l() As Integer = {1, 40, 40, 40, 40, 40, 40, 20, 20, 20, 20, 20, 60, 5, 4, 1, 2, 1, 1}
Dim f As New OpenRandomFiles(MailFile)
f.Widths = l
MailK = f.Count
ReDim Mail(MailK)
For i As Integer = 0 To MailK
   f.ReadLine()
   Dim s() As String = f.Strings
   With Mail(i)
      .Flag = Asc(s(0))
      .Name = s(1)
      .Spare1 = FnAsc(s(14))
      .Spare2 = Asc(s(15))
    End With
Next
f.Dispose()

首先，您声明的字段宽度为 415 而不是416.
您说最后的代码无法读取该行"，但这是什么意思?它是否显示您的错误MessageBox或从未调用过ReadFields()行，表明存在EndOfData条件.

如果显示错误框，内部异常是否会提供有关原因的更精确信息?

Firstly, the field widths are 415 NOT 416 as you state.
You say "The last code fails to read the line" but what does that mean? Does it show your error MessageBox or is the ReadFields() line never called, indicating that there is an EndOfData condition.

If your error box is displayed does the inner exception give more precise information about the cause?

这篇关于读取随机访问文件的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！