如何直接读取dbf/dbt文件？

Question

有谁知道如何直接从dBase .DBF/.DBT文件集中读取数据？

详情：

我试图根据规格的dBase的DBF/DBT文件写一个解析器。

DBF文件相对简单，MEMO字段中的值是该字段的数据应该始于dbt文件中的顺序块编号。

DBT文件在规范中没有深入定义。当我解析DBT文件时（根据规范由连续块组成[每个大小为512字节]，块0是头块），我看到散布在记录数据之间的额外字节数据（有些看起来像“垃圾”二进制数据，有些看起来像数据库中的其他表名）。对于一些包含字母/数字的额外数据，它试图只读取几乎不可能的块的记录数据。在我能看到的规格中没有对这些奇怪数据的清晰定义。我假设它可能是某种标题数据，但它似乎没有固定的字节宽度，甚至不出现在每个块的相同位置。

此外，DBF文件的备注字段中的顺序块编号并不总是与实际数据对齐。即dbf中的记录2表示它从块2开始，但实际上在dbt文件中从块6开始。

有没有人知道关于DBT文件结构的更多信息？也许我失踪的东西？

代码示例（VB.Net）：

' Holds information about data in the header .dbf file. 
Public Class HeaderFileClass 
    Public Property AccountNo As String  ' 6 bytes 
    Public Property BlockNumber As String '10 bytes 
    Public Property DateInfo As String  '8 bytes 
    Public Property EditBy As String  '3 bytes 
    Public Sub New() 
     AccountNo = String.Empty 
     BlockNumber = String.Empty 
     DateInfo = String.Empty 
     EditBy = String.Empty 
    End Sub 
    Public Sub New(newAcctNo As String, newBlockNo As String, newDateInf As String, newEditBy As String) 
     AccountNo = newAcctNo 
     BlockNumber = newBlockNo 
     DateInfo = newDateInf 
     EditBy = newEditBy 
    End Sub 
End Class 
' Strips a byte array of anything but alpha-numerics, space, or line feed. 
Private Function CleanBytes(ByRef bytes As Byte()) As Byte() 
    Dim newBytes As Byte() 
    Dim BLOCKSIZE As Integer = 512 
    Dim j As Integer = 0 
    Dim strOut As String = String.Empty 
    ReDim newBytes(BLOCKSIZE) 
    newBytes.Initialize() 
    For Each i As Byte In bytes 
     Dim intVal As Integer = Convert.ToInt32(i) 
     If (intVal >= 32 And intVal <= 126) Or intVal = 10 Then 
      newBytes(j) = i 
      j += 1 
     End If 
    Next 
    Return newBytes 
End Function 
Private Sub ParseFile() 
    Dim fileName As String = "C:\dbbackup\Schalls\Schalls_CleanLegacy\Schall_Clean_DATA\PATNOTES"  ' data location. 
    Dim BLOCKSIZE As Integer = 512     ' Default block size. 
    Dim bytes As Byte() = Nothing     ' bytes to be read from dbt file. 
    Dim buffer As Char()       ' buffer to use for reading dbf file. 
    Dim hList As New List(Of HeaderFileClass)  ' DBF header data storage. 
    Dim lstData As New List(Of Byte())    ' DBT block data storage. 
    ReDim buffer(28)        ' Set size of buffer array. 

    'header file load 
    Using inFile As New StreamReader(File.Open(fileName & ".DBF", FileMode.Open)) 
     ' read DBF header lines. 
     inFile.ReadLine() 
     inFile.ReadLine() 

     ' read DBF data. 
     While inFile.Read(buffer, 0, 28) > 0 
      Dim strBuf As New String(buffer) 
      Dim acctNo As String = strBuf.Substring(0, 7) 
      Dim blockNo As String = strBuf.Substring(7, 10).Trim 
      Dim dateInfo As String = strBuf.Substring(17, 8) 
      Dim editBy As String = strBuf.Substring(25, 3) 
      hList.Add(New HeaderFileClass(acctNo, blockNo, dateInfo, editBy)) 
     End While 
    End Using 


    'memo file load 
    Using inFile As New BinaryReader(File.Open(fileName & ".DBT", FileMode.Open)) 
     ' read data sequentially by blocksize. 
     Do 
      bytes = inFile.ReadBytes(BLOCKSIZE) 
      If bytes.Length > 0 Then 
       lstData.Add(bytes) 
      End If 
     Loop While bytes.Length > 0 
    End Using 

    If hList.Count > 2 Then 
     For i As Integer = 0 To hList.Count - 2 
      Dim h As HeaderFileClass = hList(i)    ' get data for the current record from the header file data. (contains block number to start) 
      Dim h2 As HeaderFileClass = hList(i + 1)  ' get the next data for the current record. (contains next starting block number) 
      Dim intFrom As Integer = CInt(h.BlockNumber) ' starting block number. 
      Dim intTo As Integer = CInt(h2.BlockNumber)  ' next record's starting block number. 
      Dim sbStr As New System.Text.StringBuilder  ' output string. 

      ' read the bytes, ensure they are text data, 
      For j As Integer = intFrom To intTo - 1 
       sbStr.Append(System.Text.Encoding.ASCII.GetString(CleanBytes(lstData(j)))) 
      Next 
      Debug.Print(sbStr.ToString) 
     Next 
    End If 
End Sub 

Answer 1

您需要使用OLEDB，例如：

Imports System.Data.OleDb 
Public Class Form1 
    Private FileName As String = IO.Path.Combine(Application.StartupPath, "Customer.dbf") 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load 
     If IO.File.Exists(FileName) Then 
      Dim Builder As New OleDbConnectionStringBuilder With 
       { 
        .DataSource = IO.Path.GetDirectoryName(FileName), 
        .Provider = "Microsoft.Jet.OLEDB.4.0" 
       } 
      Builder.Add("Extended Properties", "dBase III") 
      Using cn As New OleDb.OleDbConnection With {.ConnectionString = Builder.ConnectionString} 
       Using cmd As New OleDbCommand With {.Connection = cn} 
        cmd.CommandText = "SELECT * FROM " & IO.Path.GetFileName(FileName) 
        cn.Open() 
        Dim dt As New DataTable 
        dt.Load(cmd.ExecuteReader) 
       End Using 
      End Using 
     End If 
    End Sub 
End Class