DBASE .DBF File Structure

by Borland

Please note that the text below is a reproduction of a text file Borland distributed as a file format specification, as such it is both outdated as it has not been changed since 1998 and also is not covered by the Attribution-Share Alike 3.0 licence like the rest of the EDM/2 Wiki but is copyrighted work owned by the Borland Corporation. TI838D.txt  dBASE .DBF File Structure Category  :Database Programming Platform   :All Product   :Delphi  All

Description: Sometimes it is necessary to delve into a dBASE table outside the control of the Borland Database Engine (BDE). For instance, if the .DBT file (that contains memo data) for a given table is irretrievably lost, the file will not be usable because the byte in the file header indicates that there should be a corresponding memo file. This necessitates toggling this byte to indicate no such accompanying memo file. Or, you may just want to write your own data access routine.

Below are the file structures for dBASE table files. Represented are the file structures as used for various versions of dBASE: dBASE III PLUS 1.1, dBASE IV 2.0, dBASE 5.0 for DOS, and dBASE 5.0 for Windows.

The data file header structure for dBASE III PLUS table file.

The table file header:

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Byte Contents    Description -    0     1 byte      Valid dBASE III PLUS table file (03h without a memo                   (.DBT file; 83h with a memo).

1-3  3 bytes     Date of last update; in YYMMDD format. 4-7  32-bit      Number of records in the table. number 8-9  16-bit      Number of bytes in the header. number 10-11 16-bit     Number of bytes in the record. number 12-14 3 bytes    Reserved bytes. 15-27 13 bytes   Reserved for dBASE III PLUS on a LAN. 28-31 4 bytes    Reserved bytes. 32-n 32 bytes    Field descriptor array (the structure of this array is      each        shown below) n+1  1 byte      0Dh stored as the field terminator.

n above is the last byte in the field descriptor array. The size of the array depends on the number of fields in the table file.

Table Field Descriptor Bytes

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Byte Contents    Description -    0-10  11 bytes    Field name in ASCII (zero-filled). 11   1 byte      Field type in ASCII (C, D, L, M, or N). 12-15 4 bytes    Field data address (address is set in memory; not useful                  on disk). 16   1 byte      Field length in binary. 17   1 byte      Field decimal count in binary. 18-19 2 bytes    Reserved for dBASE III PLUS on a LAN. 20   1 byte      Work area ID. 21-22 2 bytes    Reserved for dBASE III PLUS on a LAN. 23   1 byte      SET FIELDS flag. 24-31 1 byte     Reserved bytes.

Table Records

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The records follow the header in the table file. Data records are preceded by one byte, that is, a space (20h) if the record is not deleted, an asterisk (2Ah) if the record is deleted. Fields are packed into records without field separators orrecord terminators. The end of the file is marked by a single byte, with the end-of-file marker, an OEM code page character value of 26 (1Ah). You can input OEM code page data as indicated below.

Allowable Input for dBASE Data Types

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Data Type     Data Input -- --- C (Character) All OEM code page characters. D (Date)      Numbers and a character to separate month, day, and year (stored internally as 8 digits in YYYYMMDD format). N (Numeric)   -. 0 1 2 3 4 5 6 7 8 9 L (Logical)   ? Y y N n T t F f (? when not initialized). M (Memo)      All OEM code page characters (stored internally as 10                digits representing a .DBT block number).

Binary, Memo, and OLE Fields And .DBT Files

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Memo fields store data in .DBT files consisting of blocks numbered sequentially (0, 1, 2, and so on). The size of these blocks are internally set to 512 bytes. The first block in the .DBT file, block 0, is the .DBT file header.

Memo field of each record in the .DBF file contains the number of the block (in OEM code page values) where the field's data actually begins. If a field contains no data, the .DBF file contains blanks (20h) rather than a number.

When data is changed in a field, the block numbers may also change and the number in the .DBF may be changed to reflect the new location.

This information is from the Using dBASE III PLUS manual, Appendix C.

The data file header structure for dBASE IV 2.0 table file.

File Structure:

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Byte    Contents       Meaning --- --     - 0        1byte          Valid dBASE IV file; bits 0-2 indicate version number, bit 3 the presence of a dBASE IV memo file, bits 4-6 the presence of an SQL table, bit 7 the presence of any memo file (either dBASE III                       PLUS or dBASE IV). 1-3     3 bytes        Date of last update; formattted as YYMMDD. 4-7     32-bit number  Number of records in the file. 8-9     16-bit number  Number of bytes in the header. 10-11   16-bit number  Number of bytes in the record. 12-13   2 bytes        Reserved; fill with 0. 14      1 byte         Flag indicating incomplete transaction. 15      1 byte         Encryption flag. 16-27   12 bytes       Reserved for dBASE IV in a multi-user environment. 28      1 bytes        Production MDX file flag; 01H if there is an MDX, 00H if not. 29      1 byte         Language driver ID. 30-31   2 bytes        Reserved; fill with 0. 32-n*   32 bytes each  Field descriptor array (see below). n + 1   1 byte         0DH as the field terminator.

depends on the number of fields in the database file.
 * n is the last byte in the field descriptor array. The size of the array

The field descriptor array:

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Byte    Contents       Meaning ---    -- 0-10     11 bytes       Field name in ASCII (zero-filled). 11      1 byte         Field type in ASCII (C, D, F, L, M, or N). 12-15   4 bytes        Reserved. 16      1 byte         Field length in binary. 17      1 byte         Field decimal count in binary. 18-19   2 bytes        Reserved. 20      1 byte         Work area ID. 21-30   10 bytes       Reserved. 31      1 byte         Production MDX field flag; 01H if field has an                         index tag in the production MDX file, 00H if not.

Database records:

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The records follow the header in the database file. Data records are preceded by one byte; that is, a space (20H) if the record is not deleted, an asterisk (2AH) if the record is deleted. Fields are packed into records without field separators or record terminators. The end of the file is marked by a single byte, with the end-of-file marker an ASCII 26 (1AH) character.

Allowable Input for dBASE Data Types:

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Data Type           Data Input --    - C     (Character)    All OEM code page characters. D    (Date)         Numbers and a character to separate month, day, and year (stored internally as 8 digits in YYYYMMDD                    format). F    (Floating      - . 0 1 2 3 4 5 6 7 8 9      point binary      numeric) N    (Binary        - . 0 1 2 3 4 5 6 7 8 9      coded decimal      numeric) L    (Logical)      ? Y y N n T t F f (? when not initialized). M    (Memo)         All OEM code page characters (stored internally as 10                     digits representing a .DBT block number).

Memo Fields And .DBT Files

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Memo fields store data in .DBT files consisting of blocks numbered sequentially (0, 1, 2, and so on). SET BLOCKSIZE determines the size of each block. The first block in the .DBT file, block 0, is the .DBT file header.

Each memo field of each record in the .DBF file contains the number of the block (in OEM code page values) where the field's data actually begins. If a field contains no data, the .DBF file contains blanks (20h) rather than a number.

When data is changed in a field, the block numbers may also change and the number in the .DBF may be changed to reflect the new location.

This information is from the dBASE IV Language Reference manual, Appendix D.

The data file header structure for dBASE 5.0 for DOS table file.

The table file header:

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Byte Contents    Description -    0     1 byte      Valid dBASE for Windows table file; bits 0-2 indicate version number; bit 3 indicates presence of a dBASE IV                 or dBASE for Windows memo file; bits 4-6 indicate the presence of a dBASE IV SQL table; bit 7 indicates the presence of any .DBT memo file (either a dBASE III PLUS                 type or a dBASE IV or dBASE for Windows memo file). 1-3  3 bytes     Date of last update; in YYMMDD format. 4-7  32-bit      Number of records in the table. number 8-9  16-bit      Number of bytes in the header. number 10-11 16-bit     Number of bytes in the record. number 12-13 2 bytes    Reserved; filled with zeros. 14   1 byte      Flag indicating incomplete dBASE transaction. 15   1 byte      Encryption flag. 16-27 12 bytes   Reserved for multi-user processing. 28   1 byte      Production MDX flag; 01h stored in this byte if a prod- uction .MDX file exists for this table; 00h if no .MDX file exists. 29   1 byte      Language driver ID. 30-31 2 bytes    Reserved; filled with zeros. 32-n 32 bytes    Field descriptor array (the structure of this array is      each        shown below) n+1  1 byte      0Dh stored as the field terminator.

n above is the last byte in the field descriptor array. The size of the array depends on the number of fields in the table file.

Table Field Descriptor Bytes

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Byte Contents    Description -    0-10  11 bytes    Field name in ASCII (zero-filled). 11   1 byte      Field type in ASCII (B, C, D, F, G, L, M, or N). 12-15 4 bytes    Reserved. 16   1 byte      Field length in binary. 17   1 byte      Field decimal count in binary. 18-19 2 bytes    Reserved. 20   1 byte      Work area ID. 21-30 10 bytes   Reserved. 31   1 byte      Production .MDX field flag; 01h if field has an index tag in the production .MDX file; 00h if the field is not indexed.

Table Records

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The records follow the header in the table file. Data records are preceded by one byte, that is, a space (20h) if the record is not deleted, an asterisk (2Ah) if the record is deleted. Fields are packed into records without field separators orrecord terminators. The end of the file is marked by a single byte, with the end-of-file marker, an OEM code page character value of 26 (1Ah). You can input OEM code page data as indicated below.

Allowable Input for dBASE Data Types

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Data Type     Data Input -- --- C (Character) All OEM code page characters. D (Date)      Numbers and a character to separate month, day, and year (stored internally as 8 digits in YYYYMMDD format). F (Floating   - . 0 1 2 3 4 5 6 7 8 9  point binary  numeric) N (Numeric)   -. 0 1 2 3 4 5 6 7 8 9 L (Logical)   ? Y y N n T t F f (? when not initialized). M (Memo)      All OEM code page characters (stored internally as 10               digits representing a .DBT block number).

Memo Fields And .DBT Files

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Memo fields store data in .DBT files consisting of blocks numbered sequentially (0, 1, 2, and so on). SET BLOCKSIZE determines the size of each block. The first block in the .DBT file, block 0, is the .DBT file header.

Each memo field of each record in the .DBF file contains the number of the block (in OEM code page values) where the field's data actually begins. If a field contains no data, the .DBF file contains blanks (20h) rather than a number.

When data is changed in a field, the block numbers may also change and the number in the .DBF may be changed to reflect the new location.

Unlike dBASE III PLUS, if you delete text in a memo field, dBASE 5.0 for DOS may reuse the space from the deleted text when you input new text. dBASE III PLUS always appends new text to the end of the .DBT file. In dBASE III PLUS, the .DBT file size grows whenever new text is added, even if other text in the file is deleted.

This information is from the dBASE for DOS Language Reference manual, Appendix C.

The data file header structure for dBASE 5.0 for Windows table file.

The table file header:

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Byte Contents    Description -    0     1 byte      Valid dBASE for Windows table file; bits 0-2 indicate version number; bit 3 indicates presence of a dBASE IV                 or dBASE for Windows memo file; bits 4-6 indicate the presence of a dBASE IV SQL table; bit 7 indicates the presence of any .DBT memo file (either a dBASE III PLUS                 type or a dBASE IV or dBASE for Windows memo file). 1-3  3 bytes     Date of last update; in YYMMDD format. 4-7  32-bit      Number of records in the table. number 8-9  16-bit      Number of bytes in the header. number 10-11 16-bit     Number of bytes in the record. number 12-13 2 bytes    Reserved; filled with zeros. 14   1 byte      Flag indicating incomplete dBASE IV transaction. 15   1 byte      dBASE IV encryption flag. 16-27 12 bytes   Reserved for multi-user processing. 28   1 byte      Production MDX flag; 01h stored in this byte if a prod- uction .MDX file exists for this table; 00h if no .MDX file exists. 29   1 byte      Language driver ID. 30-31 2 bytes    Reserved; filled with zeros. 32-n 32 bytes    Field descriptor array (the structure of this array is      each        shown below) n+1  1 byte      0Dh stored as the field terminator.

n above is the last byte in the field descriptor array. The size of the array depends on the number of fields in the table file.

Table Field Descriptor Bytes

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Byte Contents    Description -    0-10  11 bytes    Field name in ASCII (zero-filled). 11   1 byte      Field type in ASCII (B, C, D, F, G, L, M, or N). 12-15 4 bytes    Reserved. 16   1 byte      Field length in binary. 17   1 byte      Field decimal count in binary. 18-19 2 bytes    Reserved. 20   1 byte      Work area ID. 21-30 10 bytes   Reserved. 31   1 byte      Production .MDX field flag; 01h if field has an index tag in the production .MDX file; 00h if the field is not indexed.

Table Records

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The records follow the header in the table file. Data records are preceded by one byte, that is, a space (20h) if the record is not deleted, an asterisk (2Ah) if the record is deleted. Fields are packed into records without field separators orrecord terminators. The end of the file is marked by a single byte, with the end-of-file marker, an OEM code page character value of 26 (1Ah). You can input OEM code page data as indicated below.

Allowable Input for dBASE Data Types

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Data Type     Data Input -- --- B (Binary)    All OEM code page characters (stored internally as 10               digits representing a .DBT block number). C (Character) All OEM code page characters. D (Date)      Numbers and a character to separate month, day, and year (stored internally as 8 digits in YYYYMMDD format). G (General    All OEM code page characters (stored internally as 10 digits or OLE) representing a .DBT block number). N (Numeric)   -. 0 1 2 3 4 5 6 7 8 9 L (Logical)   ? Y y N n T t F f (? when not initialized). M (Memo)      All OEM code page characters (stored internally as 10               digits representing a .DBT block number).

Binary, Memo, and OLE Fields And .DBT Files

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Binary, memo, and OLE fields store data in .DBT files consisting of blocks numbered sequentially (0, 1, 2, and so on). SET BLOCKSIZE determines the size of each block. The first block in the .DBT file, block 0, is the .DBT file header.

Each binary, memo, or OLE field of each record in the .DBF file contains the number of the block (in OEM code page values) where the field's data actually begins. If a field contains no data, the .DBF file contains blanks (20h) rather than a number.

When data is changed in a field, the block numbers may also change and the number in the .DBF may be changed to reflect the new location.

Unlike dBASE III PLUS, if you delete text in a memo field (or binary and OLE fields), dBASE for Windows (unlike dBASE IV) may reuse the space from the deleted text when you input new text. dBASE III PLUS always appends new text to the end of the .DBT file. In dBASE III PLUS, the .DBT file size grows whenever new text is added, even if other text in the file is deleted.

This information is from the dBASE for Windows Language Reference manual, Appendix C.

Reference:

7/16/98 4:33:55 PM