DBF大字符字段 [英] DBF Large Char Field

问题描述

我有一个我相信是由Clipper创建的数据库文件，但不能肯定地说(我有用于索引的.ntx文件，我知道这是Clipper使用的文件).我正在尝试创建一个C#应用程序，该应用程序将使用System.Data.OleDB命名空间读取此数据库.

I have a database file that I beleive was created with Clipper but can't say for sure (I have .ntx files for indexes which I understand is what Clipper uses). I am trying to create a C# application that will read this database using the System.Data.OleDB namespace.

在大多数情况下，我可以成功读取表的内容，其中一个字段是我无法读取的.此字段称为CTRLNUMS，定义为CHAR(750).我已经阅读了许多通过Google搜索发现的文章，这些文章建议大于255个字符的字段必须通过与正常分配给字符串变量不同的过程来读取.到目前为止，我在找到的方法上还没有成功.

For the most part I can sucessfully read the contents of the tables there is one field that I cannot. This field called CTRLNUMS that is defined as a CHAR(750). I have read various articles found through Google searches that suggest field larger than 255 chars have to be read through a different process than the normal assignment to a string variable. So far I have not been successful in an approach that I have found.

以下是我用来读取表的示例代码片段，其中包括我用来读取CTRLNUMS字段的两个选项.这两个选项都导致返回238个字符，即使该字段中存储了750个字符也是如此.

The following is a sample code snippet I am using to read the table and includes two options I used to read the CTRLNUMS field. Both options resulted in 238 characters being returned even though there is 750 characters stored in the field.

这是我的连接字符串:

Provider = Microsoft.Jet.OLEDB.4.0;数据源= c:\ datadir;扩展属性= DBASE IV;

Provider=Microsoft.Jet.OLEDB.4.0;Data Source=c:\datadir;Extended Properties=DBASE IV;

有人可以告诉我从DBF文件读取较大字段的秘密吗?

Can anyone tell me the secret to reading larger fields from a DBF file?

using (OleDbConnection conn = new OleDbConnection(connectionString))
{
    conn.Open();

    using (OleDbCommand cmd = new OleDbCommand())
    {
        cmd.Connection = conn;
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = string.Format("SELECT ITEM,CTRLNUMS FROM STUFF WHERE ITEM = '{0}'", stuffId);

        using (OleDbDataReader dr = cmd.ExecuteReader())
        {
            if (dr.Read())
            {
                stuff.StuffId = dr["ITEM"].ToString();

                // OPTION 1
                string ctrlNums = dr["CTRLNUMS"].ToString();

                // OPTION 2
                char[] buffer = new char[750];
                int index = 0;
                int readSize = 5;
                while (index < 750)
                {
                    long charsRead = dr.GetChars(dr.GetOrdinal("CTRLNUMS"), index, buffer, index, readSize);

                    index += (int)charsRead;

                    if (charsRead < readSize)
                    {
                        break;
                    }
                }
            }
        }
    }
}

推荐答案

您可以在此处找到有关DBF结构的描述:

You can find a description of the DBF structure here: http://www.dbf2002.com/dbf-file-format.html

我认为Clipper过去所做的就是修改Field结构，以便在Character字段中，小数位保留该大小的高位字节，因此Character字段的大小实际上是256 * Decimals + Size.

What I think Clipper used to do was modify the Field structure so that, in Character fields, the Decimal Places held the high-order byte of the size, so Character field sizes were really 256*Decimals+Size.

我可能有一个读取dbfs的C#类(本机不是ADO/DAO)，可以对其进行修改以处理这种情况.让我知道您是否有兴趣.

I may have a C# class that reads dbfs (natively, not ADO/DAO), it could be modified to handle this case. Let me know if you're interested.

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