I am accessing an existing dBase IV table (created by another program) containing memos via the Microsoft Jet driver 4.0. In a C# program I am reading data, changing it and writing it back to the table. Reading works fine, writing works fine for all datatypes but memo fields: When the length of the memo field changes more than what appears to be a 512 byte block, the OLEDB driver returns an 'disk or network error' on executing the UPDATE command. Example: If the original memo size is 4323 bytes, the Update command will work fine for a string (LongVarChar) with a length between 4088 bytes and 4600 bytes.

Every string longer or shorter will fail on the disk or network exception. Has anybody had or heard of this behaviour? Every DBF tool I tried so far had no problem changing the memo length. Any help appreciated, thanks! Daffy PS: Also have tried ODBC - same error. Code Snippet dbConn = new System.Data.OleDb.

Technical Information Database TI838D.txt dBASE.DBF File Structure. The data file header structure for dBASE IV 2.0. Language driver ID. Jun 20, 2014 Visual FoxPro data adapter and Language. By a dbase dbf with data, but.

OleDbConnection (); dbConn.ConnectionString = 'Provider=Microsoft.Jet.OLEDB.4.0;Data Source=' + nd.Path + '; Extended Properties=dBASE IV;User ID=Admin;Password=;'; System.Data.OleDb. OleDbCommand myCmd= dbConn.CreateCommand(); dbConn.Open(); myCmd.CommandText = 'UPDATE myTable SET [columnname]= @memoparam WHERE myColumn1 LIKE ' + (( int )intname).ToString( 'd5' ) + ' AND myColumn2 LIKE ' + nd.ObjectNumber.ToString( 'd5' ) + ';'; myCmd.Parameters.Add( new System.Data.OleDb. OleDbParameter ( 'memoparam', System.Data.OleDb. OleDbType.LongVarWChar)); myCmd.Parameters[ 'memoparam' ].Value = writeString; updatedRows = myCmd.ExecuteNonQuery(); dbConn.Close(). The problem with writing to dbase iv files is that the information your looking for is stored in the.dbt for memo fields. When the update statement executes, there is no error, because the field exists, but stores a pointer to a position in the.dbt file.

When executing, the.dbt file is not written to. I've had similar issues trying to update a memo field in a.dbf. Only way I found round it was to open the.dbt file directly, and adjust this. This requires quite a bit of extra coding to make your program be able to read and write in.dbt format. I'm still doing this bit - will post code in vb.net up here when done.

This section may need to be rewritten entirely to comply with Wikipedia's.. The may contain suggestions. (April 2015) The original database was started by in 1978 and was known as Project Vulcan. At the time the file that held the data was a simple table that could have data added, modified, deleted and printed using ASCII characters set. As the product became more popular, the underlying file type.dbf was expanded and additional files were added to increase the capabilities of the database system.

Keep in mind that is an (integrated development environment), a database system, a compiler, and a database application builder. However, underneath all that is the.dbf file, which is the actual data storage mechanism. If you want to understand the structure at a much lower level, review the Level 5 DOS headers section of this article. File architecture overview [ ] Project Vulcan (Level 1) There are no public records on the exact layout of the file the best information at this time is that it was a simple table that allows for adding, deleting, modifying, and printing out ASCII information. It was designed to run on 8-bit machine running. Microsoft Encarta Kids 2017. DBASE II – MS-DOS (Level 2) was the first major release of and offered many advancements above and beyond the simple table structure of the original tables found in Project Vulcan. Growing Object Oriented Software Guided By Tests Ebook on this page. • Still written for 8-bit computing • Increased the number of fields from 16 to 32 • Introduced a SORT routine • 16-bit version finally released in April 1983 version 2.4 dBASE III – MSDOS (Level 2sh) was now completely focused on 16-bit operations and was introduced in 1.0 was released in June 1984.