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Table File Structure (.dbc, .dbf, .frx, .lbx, .mnx, .pjx, .scx, .vcx)

  • Article

Visual FoxPro uses tables to store data that defines different file types. The following list includes the file types that are saved as tables:

  • Database (.dbc)

  • Form (.scx)

  • Label (.lbx)

  • Menu (.mnx)

  • Project (.pjx)

  • Report (.frx)

  • Table (.dbf)

  • Visual class library (.vcx)

You can use and browse these files in the same way that you browse any table file because these files are actually tables.

A table file consists 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. The header record starts at file position zero. Data records follow the header, in consecutive bytes, and contain the actual text of the fields.

Note

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.

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.

For information about the table structures of the different file types, see Table Structures of Table Files.

Table Header Record Structure

Byte offset Description

0

File type: 0x01

FoxBASE: 0x02

FoxBASE+/Dbase III plus, no memo: 0x2F

Visual FoxPro: 0x30

Visual FoxPro, autoincrement enabled: 0x31

Visual FoxPro, Varchar, Varbinary, or Blob-enabled: 0x42

dBASE IV SQL table files, no memo: 0x62

dBASE IV SQL system files, no memo: 0x82

FoxBASE+/dBASE III PLUS, with memo: 0x8A

dBASE IV with memo: 0xCA

dBASE IV SQL table files, with memo: 0xF4

FoxPro 2.x (or earlier) with memo: 0xFA

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

28

Table flags: 0x01   file has a structural .cdx 0x02   file has a Memo field 0x04   file is a database (.dbc) This byte can contain the sum of any of the above values. For example, the value 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. One field subrecord exists 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, which is the relative path of an associated database (.dbc) file, information. If the first byte is 0x00, the file is not associated with a database. Therefore, database files always contain 0x00.

Field Subrecords Structure

Byte offset Description

0 – 10

Field name with a maximum of 10 characters. If less than 10, it is padded with null characters (0x00).

11

Field type:

W   -   Blob

C   –   Character

C   –   Character (binary)

Y   –   Currency

B   –   Double

D   –   Date

T   –   DateTime

F   –   Float

G   –   General

I   –   Integer

L   –   Logical

M   –   Memo

M   –   Memo (binary)

N   –   Numeric

P   –   Picture

Q   -   Varbinary

V   -   Varchar

V   -   Varchar (binary)

Note

For each Varchar and Varbinary field, one bit, or "varlength" bit, is allocated in the last system field, which is a hidden field and stores the null status for all fields that can be null. If the Varchar or Varbinary field can be null, the null bit follows the "varlength" bit. If the "varlength" bit is set to 1, the length of the actual field value length is stored in the last byte of the field. Otherwise, if the bit is set to 0, length of the value is equal to the field size.

12 – 15

Displacement of field in record

16

Length of field (in bytes)

17

Number of decimal places

18

Field flags: 0x01   System Column (not visible to user) 0x02   Column can store null values 0x04   Binary column (for CHAR and MEMO only) 0x06   (0x02+0x04) When a field is NULL and binary (Integer, Currency, and Character/Memo fields) 0x0C   Column is autoincrementing

19 - 22

Value of autoincrement Next value

23

Value of autoincrement Step value

24 – 31

Reserved

For information about limitations on characters per record, maximum fields, and so on, see Visual FoxPro System Capacities.

Remarks

Visual FoxPro modifies the table header when you turn on or add autoincrementing for field values.

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

  • DateTime, 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.

See Also

Tasks

How to: Check for Differences in Forms, Reports, and Other Table Files

Reference

Code Pages Supported by Visual FoxPro
Visual FoxPro Data and Field Types
Table Structures of Table Files (.dbc, .frx, .lbx, .mnx, .pjx, .scx, .vcx)
File Extensions and File Types

Other Resources

File Structures