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diff --git a/docs/html/xbc3.html b/docs/html/xbc3.html new file mode 100755 index 0000000..f2f4a1d --- /dev/null +++ b/docs/html/xbc3.html @@ -0,0 +1,73 @@ +<!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 11/21/22</p><hr> + +<br><br> +The main objective of this chapter is to provide basic information regarding +various field types supported by the library.<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 table 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 +slightly more efficient than accessing by name.<br><br> + +<h2>Strings</h2> + +Xbase64 includes support for a string class <em>xbString</em>. +The xbString class interface was originally 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 be similar. +Strings can be used to manage strings of character data. +<br><br> +<hr> +<p><img src="xbase.jpg"><hr> +</BODY> +</HTML> |