Don't we need permission to post stuff ripped out of the help file?
Nope - you are allowed to quote excerpts from copyrighted works - rule of thumb: up to 10%. -- CFK
I'm not sure this measures up to "Fair Use", since it is available online anyway. *Note...PDF file http://www.loc.gov/copyright/fls/fl102.pdf besides we aren't in Kansas,we are in Canada, their rules apply... Scott
Online help for "Table File Structure"
A table file is made up of a header record and data records. The header record defines the structure of the table and contains any other information related to the table. It starts at file position zero. The data records* follow the header (in consecutive bytes) and contain the actual text of the fields.
The length of a record (in bytes) is determined by summing the defined lengths of all fields. Integers in table files are stored with the least significant byte first.
*The data in the data file starts at the position indicated in bytes 8 to 9 of the header record. Data records begin with a delete flag byte. If this byte is an ASCII space (0x20) the record is not deleted; if the first byte is an asterisk (0x2A) the record is deleted. The data from the fields named in the field subrecords follows the delete flag.
Table Header Record Structure
|0||Type of file:
0x02 - Fox BASE
0x03 - FoxBASE+/dBASE III PLUS, no memo
0x30 - Visual FoxPro
0x31 - Visual FoxPro, autoincrement enabled
0x32 - Visual FoxPro, Varchar, Varbinary, or Blob-enabled
0x43 - dBASE IV SQL table files, no memo
0x63 - dBASE IV SQL system files, no memo
0x83 - FoxBASE+/dBASE III PLUS, with memo
0x8B - dBASE IV with memo
0xCB - dBASE IV SQL table files, with memo
0xF5 - FoxPro 2.x (or earlier) with memo
0xFB - Fox BASE
|1 � 3||Last update (YYMMDD) |
|4 � 7||Number of records in file |
|8 � 9||Position of first data record |
|10 � 11||Length of one data record (including delete flag) |
|12 � 27||Reserved |
0x01 - file has a structural .cdx
0x02 - file has a Memo field
0x04 - file is a database (.dbc)
Note that this byte can contain the sum of
any of the above values. For example, 0x03
indicates the table has a structural .cdx
and a Memo field.
|29||Code page mark |
|30 � 31||Reserved, contains 0x00 |
|32 � n||Field subrecords|
The number of fields determines the number of field subrecords. There is one field subrecord for each field in the table.
|n+1||Header record terminator (0x0D)|
|n+2 to n+264||A 263-byte range that contains the backlink information (the relative path of an associated database (.dbc)). If the first byte is 0x00 then the file is not associated with a database. Hence, database files themselves always contain 0x00.|
Field Subrecords Structure
|Byte offset ||Description|
|0 � 10
||Field name (maximum of 10 characters; if less than 10, it is padded with null character (0x00))
C 0x43 Character
Y 0x59 Currency
N 0x4E Numeric
F 0x46 Float
D 0x44 Date
T 0x54 Date Time
B 0x42 Double
I 0x49 Integer
L 0x4C Logical
M 0x4D Memo
G 0x47 General
C 0x43 Character (binary)
M 0x4D Memo (binary)
P 0x50 Picture
Q 0x51 Varbinary
V 0x56 Varchar
V 0x56 Varchar (binary)
W 0x57 Blob
|12 � 15
||Displacement of field in record
||Length of field (in bytes)
||Number of decimal places
0x01 System Column (not visible to user)
0x02 Column can store null values
0x04 Binary column (for CHAR and MEMO only)
|19 � 32
For information about limitations on characters per record, maximum fields, and so on, see Visual FoxPro System Capacities.
Visual FoxPro does not modify the header of a file that has been saved to a FoxPro 2.x file format unless one of the following features has been added to the file:
- Null value support
- Date Time, Currency, and Double data types
- CHAR or MEMO field is marked as Binary
- A table is added to a database (.dbc) file
Tip You can use the following formula to return the number of fields in a table file:
(x � 296/32). In the formula,
x is the position of the first record (bytes 8 to 9 in the table header record), 296 is 263 (backlink info) + 1 (header record terminator) + 32 (first field subrecord), and 32 is the length of a field subrecord.
Q: Is it possible to change table format from VFP to Fox2x without using VFP, by simple file manipulation if the table doesn't use new VFP features?
A: Yes it can be done by overriding the first byte (offset 0) of the table header with appropriate value.
Category Reference Category Data
( Topic last updated: 2010.03.29 12:17:33 PM )