File format of dBase and FoxPro data bases
 
*** Question
Does anyone know where I might get some info on the structures of Dbase
(.DBF) files?
 
*** Answer
Here's what I was able to dig up:
===
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(1) 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.
Numbers in this file are represented in reverse bytes.
 
* Table Header Record
Bytes Description
00 Type of data file:
FoxBASE+/dBASE III PLUS, no memo -- 0x03
FoxBASE+/dBASE III PLUS, with memo -- 0x83
FoxPro/dBASE IV, no memo -- 0x03
FoxPro with memo -- 0xF5
dBASE IV with memo -- 0x8B
01-03 Last update (YYMMDD)
04-07 Number of records in file
08-09 Position of first data record
10-11 Length of one data record (including delete flag)
12-31 Reserved
32-n Field subrecords(2)
n + 1 Header record terminator (0x0D)
 
* Field Subrecords(3)
Bytes Description
00-10 Field name (maximum of 10 characters -- if less than 10
it
is padded with null character (0x00))
11 Data Type:
C - Character
N - Numeric
L - Logical
M - Memo
G - General
D - Date
F - Float
P - Picture
12-15 Displacement of field in record
16 Length of field (in bytes)
17 Number of decimal places
18-32 Reserved
 
* Notes to Data File Structure
 

(1) The data in the data file starts at the position indicated in bytes
08-09 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.

(2) The number of fields determines the number of field subrecords.
There is one field subrecord for each field in the table.


Answer 4
~~~~~~~~~~~~~~~~~~
[ from Wouter Bergmann Tiest's BASIC-FAQ - www.fys.ruu.nl/~bergmann/basic-faq.html ]
 

How To Read A dBASE .DBF-File?
 
Look at the program PRINTDBF.BAS to see how to print listings of dBase III+ or IV .DBF-files. The code came from Jos Szabo.
 
'=================================================
'= PROGRAM: PRINTDBF.BAS =
'= PURPOSE: Print listings of dBASE III+/IV =
'= DBF files =
'=================================================
DEFINT A-Z
DECLARE FUNCTION ReadFileStructure% ()
DECLARE FUNCTION RightJust$ (Value$, FieldWidth%)
DECLARE FUNCTION ZeroJust$ (Number AS INTEGER)
DECLARE FUNCTION ReadDbfHdr% ()
DECLARE SUB DspDbfInfo ()
DECLARE SUB DspFileStructure ()
DECLARE SUB Pause ()
DECLARE SUB PrintDbfRecord (fv$(), RecNum%)
DECLARE SUB PrintReport ()
DECLARE SUB ReadDbfRecord (fv$())


'-------------------------------------------------
' Initialize variables and create types -
'-------------------------------------------------

CONST True = -1, False = 0

TYPE HeaderInfoType
VersionNumber AS INTEGER
LastUpdate AS STRING * 8
NumberRecords AS LONG
HeaderLength AS INTEGER
RecordLength AS INTEGER
NumberFields AS INTEGER
FileSize AS LONG
END TYPE

TYPE FieldInfoType
FdName AS STRING * 11
FdType AS STRING * 1
FdLength AS INTEGER
FdDec AS INTEGER
END TYPE

DIM SHARED Hdr AS HeaderInfoType
DIM SHARED FileName$

FileName$ = "PLANETS.DBF"

'-------------------------------------------------
' Main processing loop -
'-------------------------------------------------

OPEN FileName$ FOR BINARY AS #1
CLS
ActionHdr = ReadDbfHdr
SELECT CASE ActionHdr
CASE 1
BEEP
PRINT "Not a dBASE III+ or IV file"
CASE ELSE
DspDbfInfo
Pause
DIM SHARED FLDS(Hdr.NumberFields)_
AS FieldInfoType
ActionFile = ReadFileStructure
SELECT CASE ActionFile
CASE True
CLS
DspFileStructure
Pause
IF ActionHdr <> 2 THEN
CLS
PrintReport
Pause
ELSE
CLS
PRINT "No records to print"
END IF
CASE False
BEEP
PRINT "Field information error"
END SELECT
END SELECT
CLOSE #1
END

SUB DspDbfInfo

'-------------------------------------------------
'Display dBASE file header information -
'-------------------------------------------------

PRINT USING "dBASE Version : #";_
Hdr.VersionNumber
PRINT "Database in use : "; FileName$
PRINT USING "Number of data records: ########";_
Hdr.NumberRecords
PRINT "Date of last update : "; Hdr.LastUpdate
PRINT USING "Header length : ####";_
Hdr.HeaderLength
PRINT USING "Record length : ####";_
Hdr.RecordLength
PRINT USING "Number of fields : ###";_
Hdr.NumberFields
PRINT USING "File size : ########";_
Hdr.FileSize

END SUB

SUB DspFileStructure

'-------------------------------------------------
'Purpose: Display the structure of the dBASE file-
' Name, Field Type, Length and number -
' of decimals if a number -
'-------------------------------------------------

FieldTitleS$ =_
"Field Field Name Type Width Dec"
FieldString1$ = " ### \ \ "
FieldString2$ = "\ \ ### ##"

PRINT : PRINT FieldTitleS$

FOR I = 1 TO Hdr.NumberFields
PRINT USING FieldString1$; I; FLDS(I).FdName;
SELECT CASE FLDS(I).FdType
CASE "C": ty$ = "Character"
CASE "L": ty$ = "Logical"
CASE "N": ty$ = "Number"
CASE "F": ty$ = "Floating Pt"
CASE "D": ty$ = "Date"
CASE "M": ty$ = "Memo"
CASE ELSE: ty$ = "Unknown"
END SELECT
PRINT USING FieldString2$; ty$;_
FLDS(I).FdLength; FLDS(I).FdDec
NEXT I
PRINT " ** Total **"; TAB(33);
PRINT USING "####"; Hdr.RecordLength

END SUB

SUB Pause
PRINT
PRINT "Press any key to continue"
WHILE INKEY$ = "": WEND
END SUB

SUB PrintDbfRecord (fv$(), RecNum)

'-------------------------------------------------
'Purpose: Print the record to the screen. Left -
' justify character, date and logical -
' fields. Right justify numeric fields -
' and ignore memo fields -
'Input : Field values store in character array, -
' current record number -
'-------------------------------------------------

' Print rec # & delete status
ColumnSpace = 4 'Room between columns
PRINT USING "####### !"; RecNum; fv$(0);

ColumnLocation = 10 'Set current location
FOR I = 1 TO Hdr.NumberFields
IF FLDS(I).FdType <> "M" THEN
PRINT TAB(ColumnLocation);
IF FLDS(I).FdType = "N" OR _
FLDS(I).FdType = "F" THEN
PRINT RightJust$(fv$(I), FLDS(I).FdLength);
ELSE
PRINT fv$(I);
END IF
' Set next print location
ColumnLocation = ColumnLocation +_
FLDS(I).FdLength + ColumnSpace
END IF
NEXT I
PRINT

END SUB

SUB PrintReport

'-------------------------------------------------
'Purpose: Main printing routine -
'Calls : ReadDbfRecord -
' PrintDbfRecord -
'-------------------------------------------------

DIM FieldValues$(Hdr.NumberFields)
PRINT : PRINT
PRINT "Report on the "; FileName$; " file"
PRINT
FOR I = 1 TO Hdr.NumberRecords
CALL ReadDbfRecord(FieldValues$())
CALL PrintDbfRecord(FieldValues$(), I)
NEXT I
END SUB

FUNCTION ReadDbfHdr

'-------------------------------------------------
'Purpose: Read the dBASE file header information -
' and store in the header record -
'-------------------------------------------------

HdrStr$ = SPACE$(32)
GET #1, , HdrStr$ 'Read dBASE Header

Hdr.VersionNumber = ASC(LEFT$(HdrStr$, 1)) AND (7)

UpdYY$ = ZeroJust$(ASC(MID$(HdrStr$, 2, 1)))
UpdMM$ = ZeroJust$(ASC(MID$(HdrStr$, 3, 1)))
UpdDD$ = ZeroJust$(ASC(MID$(HdrStr$, 4, 1)))

Hdr.LastUpdate = UpdMM$+"/"+UpdDD$+"/"+UpdYY$

Hdr.NumberRecords = CVL(MID$(HdrStr$, 5, 4))
Hdr.HeaderLength = CVI(MID$(HdrStr$, 9, 2))
Hdr.RecordLength = CVI(MID$(HdrStr$, 11, 2))

Hdr.NumberFields = (Hdr.HeaderLength - 33) / 32
Hdr.FileSize = Hdr.HeaderLength + Hdr.RecordLength_
* Hdr.NumberRecords + 1

IF Hdr.VersionNumber <> 3 THEN
ReadDbfHdr = 1 'Not a dBASE file
EXIT FUNCTION
END IF

IF Hdr.NumberRecords = 0 THEN
ReadDbfHdr = 2 'No records
EXIT FUNCTION
END IF
ReadDbfHdr = 0 'No errors
END FUNCTION

SUB ReadDbfRecord (fv$())

'-------------------------------------------------
'Purpose: Read a dBASE record, format date and -
' logical fields for output -
'Input : Array of Field values -
'-------------------------------------------------

F$ = SPACE$(Hdr.RecordLength)
GET #1, , F$ 'Read the record

fv$(0) = LEFT$(F$, 1) 'Read deleted record mark
FPOS = 2

FOR I = 1 TO Hdr.NumberFields

fv$(I) = MID$(F$, FPOS, FLDS(I).FdLength)

SELECT CASE FLDS(I).FdType 'Adjust field types
CASE "D" 'Modify date format
y$ = LEFT$(fv$(I), 4)
M$ = MID$(fv$(I), 5, 2)
d$ = RIGHT$(fv$(I), 2)
fv$(I) = M$ + "/" + d$ + "/" + y$
CASE "L" 'Standardize T or F
SELECT CASE UCASE$(fv$(I))
CASE "Y", "T": fv$(I) = ".T."
CASE "N", "F": fv$(I) = ".F."
CASE ELSE: fv$(I) = ".?."
END SELECT
CASE ELSE
END SELECT
FPOS = FPOS + FLDS(I).FdLength 'Set next fld
' PRINT fv$(I)

NEXT I
END SUB

FUNCTION ReadFileStructure

'-------------------------------------------------
'Purpose: Read the file structure store in the -
' dBASE file header. -
'-------------------------------------------------

FOR I = 1 TO Hdr.NumberFields
Fld$ = SPACE$(32)
GET #1, , Fld$ 'Get field info string
FLDS(I).FdName = LEFT$(Fld$, 11)
FLDS(I).FdType = MID$(Fld$, 12, 1)
FLDS(I).FdLength = ASC(MID$(Fld$, 17, 1))
FLDS(I).FdDec = ASC(MID$(Fld$, 18, 1))
NEXT I
HeaderTerminator$ = INPUT$(1, #1) 'Last hdr byte
IF ASC(HeaderTerminator$) <> 13 THEN
ReadFileStructure = False 'Bad Dbf header
END IF
ReadFileStructure = True
END FUNCTION

FUNCTION RightJust$ (Value$, FieldWidth)

'-------------------------------------------------
'Purpose: Right justify a string by padding it -
' with spaces on the left -
'Input : The character value to justify, the -
' width of the field to fit -
'Output : A right justified string to print -
'-------------------------------------------------

RightJust$ = RIGHT$(STRING$(FieldWidth, " ") +_
Value$, FieldWidth)
END FUNCTION

DEFSNG A-Z
FUNCTION ZeroJust$ (Number AS INTEGER)

'-------------------------------------------------
'Purpose: Add a leading zero to numbers less -
' than 10 so they take as much room as -
' numbers 10 and larger -
'Input : The number to standardize -
'Output : The adjusted number -
'-------------------------------------------------

N$ = STR$(Number)
LengthN = LEN(N$) - 1'Subtract 1 for leading space
N$ = RIGHT$("0" + RIGHT$(N$, LengthN), 2)
ZeroJust$ = N$
END FUNCTION