Fields, Strings and Dates

Chapter Updated 06/27/25

The main objective of this chapter is to provide basic information regarding field types supported by the library.

Xbase64 Versions
dBASE Version	File Level	Xbase64 Class	Field Name Max Size	Memo File Version
III+	5	xbDbf3	10	III
IV	5	xbDbf4	10	IV
5	5	xbDbf5	10	IV
7 and higher	7	xbDbf7	31	IV

Notes on the different versions

Level 5 and Level 7 files are not interchangable.

If you are supporting older dbf file types, pick the appropriate level for your application.

If you are working on a net new project and attempting to maintain a minimal footprint with limited functionality, try using Version 3 and turn off support for everything you don't need when compiling the library.

If you are working on a new project and want maximum functionality, choose version 7 with all library compile options turned on.

If you want it all, enable everything (default).

DBF Field Types
Type	Size	Allowable Values	Xbase64 Schema Value	Level	dBASE III	dBASE IV	dBASE V	dBASE VII	Clipper 5
Character	0 - 254	Anything	XB_CHAR_FLD (C)	5,7	X	X	X	X	X
Numeric	0 - 17(include sign and decimal point	+ - . 0 through 9	XB_NUMERIC_FLD (N)	5,7	X	X	X	X	X
Date	8	CCYYMMDD	XB_DATE_FLD (D)	5,7	X	X	X	X	X
Logical	1	Y y N n T t F f	XB_LOGICAL_FLD (L)	5,7	X	X	X	X	X
Memo	Fixed length portion - 10 Variable length 0 - 32760	Type III - Text Type IV - Anything	XB_MEMO_FLD (M)	5,7	X	X	X	X	X
Floating Point	0 - 17 (includes sign and decimal point	+ - . 0 through 9	XB_FLOAT_FLD (F)	5,7		X	X	X
OLE	Fixed length portion - 10 Variable length max 2G	Object Linking and Embedding, Links to objects	XB_OLE_FLD (G)	5,7			X	X
Binary	Fixed length portion - 10 Variable length max 2G	Binary Data	XB_BINARY_FLD (B)	5,7			X	X
Long	Fixed length portion - 4	32 bit long integers	XB_LONG_FLD (I)	7				X
DateTime	Fixed length portion - 8	Date and time Number of milliseconds since 01/01/0001	XB_TIMESTAMP_FLD (@)	7				X
Double	Fixed length portion - 8	Floating point numbers	XB_DOUBLE_FLD (O)	7				X
AutoIncrement	Fixed length portion - 4	Auto increment field	XB_AUTOINCREMENT_FLD (+)	7				X

New table (dbf) Definition

Field names and charactersitics are defined when a dbf data file is initially created. If field characteristics need revision after the file is initially created, define a new version of the table and copy existing data from the old table to the new table.

Fields and Field Numbers

The Xbase64 routines can access field data via using field names or field numbers. Field numbers are numbered 0-n where the first field in a datafile is field 0 going through the last field n. Accessing fields by number is slightly more efficient than accessing by name as the routines ultimately need to determine a field number to access the data in the file.

Strings

Xbase64 includes support for a string class xbString. The xbString class interface was originally derived from the Draft Standard C++ Library by P.J. Plauger and significantly modified. If you are familiar with other string classes, this one should be similar. Strings can be used to manage strings of character data. See the xbString class for more inforomation.

Date Fields

Date fields are stored in the .DBF files as Gregorian dates with format CCYYMMDD and the library date routines work with dates formated with the same CCYYMMDD format.

Date fields in the database stored as eight spaces are considered null dates.

The library can effectivly handle leap years and leap centuries.

Julian dates are supported.

See class xbDate for a wide range of functionality for processing date values.

Memo, OLE and Blob Fields

Memo fields are supported in all versions of the software. OLE and Blob fields are supported beginning with Version 5 and use the version 4 memo format.

Memo, OLE and Blob fields are variable length data fields which are stored in two parts. This first part is a ten byte field which is stored in the fixed length record of the .DBF file. The variable data is stored in a seperate .DBT file in 512 byte blocks. The ten byte field in the fixed length portion of the record points to a .DBT block number.

There are two versions of memo data files. Version 3 supports the older version that does not support space reclamation and versions 4 and greater use the newest format which does include space reclamation of discarded blocks.

The xbString class can be used for manipulating string data which is terminated with a null terminating byte.

The xbBlob class can be used for supporting binary and OLE data types. The xbBlob class can support an object up to 2G in size, providing it is running on a strong enough machine and OS to provide that level of memory requirement.

Double

Available starting with version 7. Eight byte floating point field.

AutoIncrement

Available starting with version 7. Long integer field that auto increments when appending a new record.

TimeStamp

Available starting with version 7. Field is comprised of two long integer fields. The first represents the number of days since 1//1/4713 BC and the second is the number of seconds since midnight.

Long

Available starting with version 7. Four byte unsigned long integer field.