我正在尝试读取随机访问文件，但是我在第一个文件Error 5 (unable to read beyond end of the stream)上收到以下错误。我不确定我在这里做错了什么，我该如何解决这个问题？
Structure StdSections
'UPGRADE_WARNING: Fixed-length string size must fit in the buffer. Click for more: 'ms-help://MS.VSCC.v90/dv_commoner/local/redirect.htm?keyword="3C1E4426-0B80-443E-B943-0627CD55D48B"'
<VBFixedString(15), System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst:=15)> Public A() As Char 'BEAM --- complete beam designation 15
'UPGRADE_WARNING: Fixed-length string size must fit in the buffer. Click for more: 'ms-help://MS.VSCC.v90/dv_commoner/local/redirect.htm?keyword="3C1E4426-0B80-443E-B943-0627CD55D48B"'
<VBFixedString(2), System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst:=2)> Public B() As Char 'DSG --- shape ie "W" or "C" 2
Dim C As Single 'DN --- nominal depth of section 4
Dim d As Single 'WGT --- weight 4
.
.
.
End structure
''Note 'File1'is the existing RAF and holds complete path!
Dim i,ffr,fLength,lastmembNo as integer
sectionFound = False
Dim std As new StdSections
fLength = Len(std)
If fLength = 0 Then fLength = 168 ' 177
ffr = FreeFile()
FileOpen(ffr, File1, OpenMode.Random, OpenAccess.Read, OpenShare.LockRead, fLength)
lastmembNo = CInt(LOF(ffr)) \ fLength
For i = 1 To lastmembNo
FileGet(ffr, std, i)
>>Error 5 (unable to read beyond end of the stream) <<<
If Trim(memberID) = Trim(std.A) Then
sectionFound = True
end if
next i
答案 0 :(得分：1)
我还没有真正使用VB.NET中的旧OpenFile等文件访问方法，所以我只是在猜测，但在.NET中，许多变量类型的大小都发生了变化。例如一个整数现在是32位（4字节），我认为布尔值是不同的，虽然单个仍然是4个字节。
此外，.NET中的字符串默认为Unicode，而不是ASCII，因此您不能依赖.NET字符串变量中的1个字符= 1个字节。实际上，.NET在运行之前就会在PC上执行“JIT编译”程序，所以你不能像过去那样在内存中真正布局结构。
如果你想切换到新的“Stream”对象，这里有一些代码可以帮助你入门：
Dim strFilename As String = "C:\Junk\Junk.txt"
Dim strTest As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
Call My.Computer.FileSystem.WriteAllText(strFilename, strTest, False)
Dim byt(2) As Byte
Using fs As New FileStream(strFilename, FileMode.Open, FileAccess.ReadWrite, FileShare.ReadWrite)
fs.Seek(16, SeekOrigin.Begin)
fs.Read(byt, 0, 3)
Dim s As String = Chr(byt(0)) & Chr(byt(1)) & Chr(byt(2))
MsgBox(s)
fs.Seek(5, SeekOrigin.Begin)
fs.Write(byt, 0, 3)
End Using
Dim strModded As String = My.Computer.FileSystem.ReadAllText(strFilename)
MsgBox(strModded)
我不会因为保留旧方法而责怪你：使用新方法，你需要定义一个类，然后有一个自定义例程来从Byte（）转换为类的属性。比简单地将文件中的字节加载到内存中更多的工作。
答案 1 :(得分：0)
好的，我认为您应该切换到“.NET方式”，如下所示：
Imports System.IO
Imports System.Xml
Public Class Form1
Public Const gintRecLen_CONST As Integer = 177
Class StdSections2
Private mstrA As String
Public Property A() As String
Get
Return mstrA
End Get
Set(ByVal value As String)
If value.Length <> 15 Then
Throw New Exception("Wrong size")
End If
mstrA = value
End Set
End Property
Private mstrB As String
Public Property B() As String
Get
Return mstrB
End Get
Set(ByVal value As String)
If value.Length <> 2 Then
Throw New Exception("Wrong size")
End If
mstrB = value
End Set
End Property
Public C(39) As Single
Public Shared Function FromBytes(byt() As Byte) As StdSections2
Dim output As New StdSections2
If byt.Length <> gintRecLen_CONST Then
Throw New Exception("Wrong size")
End If
For i As Integer = 0 To 14
output.mstrA &= Chr(byt(i))
Next i
For i As Integer = 15 To 16
output.mstrB &= Chr(byt(i))
Next i
For i As Integer = 0 To 39
Dim bytTemp(3) As Byte
output.C(i) = BitConverter.ToSingle(byt, 17 + 4 * i)
Next i
Return output
End Function
End Class
Sub New()
' This call is required by the designer.
InitializeComponent()
' Add any initialization after the InitializeComponent() call.
End Sub
Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
Dim strFilename As String = "C:\Junk\Junk.txt"
Dim strMemberID As String = "foo"
Dim intRecCount As Integer = CInt(My.Computer.FileSystem.GetFileInfo(strFilename).Length) \ gintRecLen_CONST
Dim blnSectionFound As Boolean = False
Using fs As New FileStream(strFilename, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)
For intRec As Integer = 0 To intRecCount - 1
Dim intRecPos As Integer = gintRecLen_CONST * intRec
fs.Seek(intRecPos, SeekOrigin.Begin)
Dim byt(gintRecLen_CONST - 1) As Byte
fs.Read(byt, 0, gintRecLen_CONST)
Dim ss2 As StdSections2 = StdSections2.FromBytes(byt)
'MsgBox(ss2.A & ":" & ss2.C(3)) 'debugging
If strMemberID.Trim = ss2.A.Trim Then
blnSectionFound = True
Exit For
End If
Next intRec
End Using
MsgBox(blnSectionFound.ToString)
End Sub
End Class
我们定义了一个名为StdSections2的类，它使用.NET字符串和Singles数组。我们到处都使用基于0的数组。我们使用新的FileStream对象加载文件，并使用Seek（）命令查找我们想要的位置。然后我们从文件中加载原始字节，并使用Chr（）和BitConverter.ToSingle（）将原始字节转换为字符串和单个字节。
答案 2 :(得分：0)
我不确定你的例子，但是这个有效：
Public Class Form1
Const maxLenName = 30
Structure person
<VBFixedString(maxLenName)> Dim name As String
Dim age As Byte
End Structure
Private Sub Form1_Load(sender As [Object], e As EventArgs) Handles MyBase.Load
Dim entryIn As New person
Dim recordLen As Integer = Len(entryIn)
Dim entry As person
If FileIO.FileSystem.FileExists("test.raf") Then Kill("test.raf")
FileOpen(1, "test.raf", OpenMode.Random,,, recordLen)
'write
entry.name = LSet("Bill", maxLenName)
entry.age = 25
FilePut(1, entry, 6) 'write to 6th record
'read
Dim nRecords As Integer = LOF(1) \ recordLen
FileGet(1, entryIn, nRecords)
FileClose(1)
Dim personName As String = RTrim(entryIn.name)
Dim personAge As Byte = entryIn.age
MsgBox(personName & "'s age is " & personAge)
End Sub
End Class