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

  • Článek

Visual FoxPro uses tables to store data that defines different file types. The file types that are saved as table files are:

  • Table (.dbf)
  • Database (.dbc)
  • Form (.scx)
  • Label (.lbx)
  • Menu (.mnx)
  • Project (.pjx)
  • Report (.frx)
  • Visual Class Library (.vcx)

Because these files are actually tables, you can use and browse them in the same way that you browse any .dbf file.

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 records1 follow the header (in consecutive bytes) and contain the actual text of the fields.

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

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.

Table Header Record Structure

Byte offset Description
0 Type of file
0x02   FoxBASE
0x03   FoxBASE+/dBASE III PLUS, no memo
0x30   Visual FoxPro
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   FoxBASE
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)
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.

1 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.

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))
11 Field Type:
C   –   Character
Y   –   Currency
N   –   Numeric
F   –   Float
D   –   Date
T   –   DateTime
B   –   Double
I   –   Integer
L   –   Logical
M   –   Memo
G   –   General
C   –   Character (binary)
M   –   Memo (binary)
P   –   Picture
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)
19 – 32 Reserved

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

Remarks

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

Code Pages Supported by Visual FoxPro | Data and Field Types | Table Structures of Table Files (.dbc, .frx, .lbx, .mnx, .pjx, .scx, .vcx) | Visual FoxPro System Capacities. | Checking for Differences in Forms, Reports, and Other Table Files | File Extensions and File Types