From 4875a3dd9b183dcd2256e2abfc4ccf7484c233b4 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?J=C3=B6rg=20Frings-F=C3=BCrst?= Date: Wed, 7 Dec 2022 13:17:14 +0100 Subject: New upstream version 4.0.2 --- html/xbc3.htm | 91 ----------------------------------------------------------- 1 file changed, 91 deletions(-) delete mode 100755 html/xbc3.htm (limited to 'html/xbc3.htm') diff --git a/html/xbc3.htm b/html/xbc3.htm deleted file mode 100755 index b944a1b..0000000 --- a/html/xbc3.htm +++ /dev/null @@ -1,91 +0,0 @@ - - -Xbase DBMS Chapter 3 - -

Fields and Strings

-

Chapter Updated 8/20/03

- -

-The title of this chapter almost sounds like a popular North American -magazine called Field and Stream. The difference between this chapter and -that magazine is there are no dead animal carcuses or fishing lures in -this chapter. For those you will need to get a copy of Field and Stream. - -

-The main objective of this chapter is to provide information regarding the -basic concepts of manipulating data via the field methods.

- -Field names can be up to ten bytes in length and can contain characters, numbers -or special characters in the name. The field methods are used to manipulate -the data in a record of a data file. There are several types of fields.

- - - - - -

Field Types

TypeSizeAllowable ValuesSchema Value -
Numeric0 - 17(include sign and decimal point+ - . 0 through 9XB_NUMERIC_FLD -
Character0 - 254AnythingXB_CHAR_FLD -
Date8CCYYMMDDXB_DATE_FLD -
Floating Point0 - 17 (includes sign and decimal point+ - . 0 through 9XB_FLOAT_FLD -
Logical1? Y y N n T t F f (? - uninitialized)XB_LOGICAL_FLD -
MemoFixed length portion - 10
Variable length 0 - 32760 -		Type III - Text
Type IV - Anything		XB_MEMO_FLD -
- -

-Field names, types and lengths are defined when a data file is created. -After the file is created, the field characteristics can not be changed. To -change field characteristics, a new database must be defined with the new -field requirements.

- -

Memo Fields

- -Memo 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 type III and type IV. Type IV -is more advanced in that released space can be reused and it also -supports BLOB data. The type III file is older technology, does not -support dynamic space reclamation and only supports string data. -See method xbDbf::SetVersion for controlling which version type you are -using. - -

-To utilize memo fields, the application program must allocate a buffer -which is large enough to handle the memo data.

- -

Fields and Field Numbers

- -The Xbase 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 -more efficient than accessing by name.

- -

Record Schema

- -The record schema of a file can be found in the documentation for method -CreateDatabase in the Database Methods chapter, or view example program -sample1.cpp.

- -

Strings

- -Beginning with Release 1.8.0a, Xbase includes support for a string class -xbString. The original thinking was not to include a string -class in the library, and encourage users to use the string class -native to the user's compiler. But as C++ does not have a native way -to handle strings, and there is not a standard string class across C++ -compilers, it was decided to include a lightweight string class with the -library. In some cases this is redundant, but it is portable. -

-The xbString class interface was derived from the Draft Standard C++ -Library by P.J. Plauger and modified. If you are familiar with -other string classes, this one should feel similar. -

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