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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 @@ -<!DOCTYPE HTML PUBLIC> -<HTML> -<TITLE>Xbase DBMS Chapter 3</TITLE> -<BODY BGCOLOR=#FFFFFF> -<H1><p align="center">Fields and Strings</p></H1> -<p align="center">Chapter Updated 8/20/03</p><hr> - -<br><br> -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. - -<br><br> -The main objective of this chapter is to provide information regarding the -basic concepts of manipulating data via the field methods.<br><br> - -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.<br><br> - - -<TABLE BORDER> -<CAPTION ALIGN="TOP"><h3>Field Types</H3></CAPTION> -<TR VALIGN="BASELINE"> -<TR><TH ALIGN="LEFT">Type<TD>Size<TD>Allowable Values<TD>Schema Value -<TR><TH ALIGN="LEFT">Numeric<TD>0 - 17(include sign and decimal point<TD>+ - . 0 through 9<TD>XB_NUMERIC_FLD -<TR><TH ALIGN="LEFT">Character<TD>0 - 254<TD>Anything<TD>XB_CHAR_FLD -<TR><TH ALIGN="LEFT">Date<TD>8<TD>CCYYMMDD<TD>XB_DATE_FLD -<TR><TH ALIGN="LEFT">Floating Point<TD>0 - 17 (includes sign and decimal point<TD>+ - . 0 through 9<TD>XB_FLOAT_FLD -<TR><TH ALIGN="LEFT">Logical<TD>1<TD>? Y y N n T t F f (? - uninitialized)<TD>XB_LOGICAL_FLD -<TR><TH ALIGN="LEFT">Memo<TD>Fixed length portion - 10<br>Variable length 0 - 32760 -<TD>Type III - Text<br>Type IV - Anything<TD>XB_MEMO_FLD -</TABLE> - -<br><br> -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.<br><br> - -<h2>Memo Fields</h2> - -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.<br><br> - -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. - -<br><br> -To utilize memo fields, the application program must allocate a buffer -which is large enough to handle the memo data.<br><br> - -<h2>Fields and Field Numbers</h2> - -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.<br><br> - -<h2>Record Schema</h2> - -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.</A><br><br> - -<h2>Strings</h2> - -Beginning with Release 1.8.0a, Xbase includes support for a string class -<em>xbString</em>. 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. -<br><br> -The xbString class interface was derived from the <em>Draft Standard C++ -Library by P.J. Plauger</em> and modified. If you are familiar with -other string classes, this one should feel similar. -<br><br> -<hr> -<p><img src="xbase.jpg"><hr> -</BODY> -</HTML> |