TStruct / TField / TIndex

Source: source/classes/tstruct.prg, source/classes/tfield.prg, source/classes/tindex.prg

These three utility classes provide object-oriented representations for C-style memory structures (TStruct), DBF field definitions (TField), and DBF index definitions (TIndex). They are used when working with low-level data structures, defining DBF schemas programmatically, or creating index files from Harbour code.

TStruct - C Structure Builder

TStruct models a C-language structure in Harbour memory. It maintains a binary buffer and a list of member definitions, allowing members to be added and accessed by name or position.

DATA Members

Type Constants

Methods

Example: Define and Use a C Structure

#include "FiveWin.ch"
#include "Struct.ch"

function Main()

   local oStru := TStruct():New()

   // Add members: name, type, length
   oStru:AddMember( "nId",   LONG,    4 )
   oStru:AddMember( "cName", CHAR,   20 )
   oStru:AddMember( "nAge",  BYTE      )   // defaults to 1 byte

   ? "Size:", oStru:SizeOf()               // 25

   // Set values
   oStru:SetMember( 1, 12345 )
   oStru:SetMember( 2, "John Smith" )

   // Read them back
   ? oStru:GetMember( 1 )                  // 12345
   ? oStru:GetMember( 2 )                  // "John Smith"

return nil

TField - DBF Field Definition

TField is a simple data container representing a single DBF field. It stores all properties needed to define a field in a DBF file structure.

DATA Members

Method

Example: Define a DBF Field

#include "FiveWin.ch"

function Main()

   local oFld

   oFld := TField():New( "CUSTOMER.DBF", 1, .F., "CODE", "C", 5, 0, "Customer code" )

   ? oFld:cName     // "CODE"
   ? oFld:cType     // "C"
   ? oFld:nWidth    // 5

return nil

TIndex - DBF Index Definition

TIndex represents an index definition for a DBF file. It can create the actual index file on disk (CDX or NTX format) from the definition properties.

DATA Members

Methods

Example: Create an Index

#include "FiveWin.ch"

function Main()

   local oIdx

   // Define an index on CUSTOMER.DBF by the CODE field
   oIdx := TIndex():New( "CUSTOMER.DBF", "CODE_IDX", "CODE", "CODE", .F., .F., "Index by code" )

   // Create the index file
   oIdx:Create( "C:\data\" )

return nil

Notes

• TStruct uses Harbour's NumToBin() / BinToNum() internally for buffer serialization. It supports member access by both numeric index and name (via error handler).
• TField is primarily a data container and does not modify the DBF file itself. It is useful for programmatic schema construction and metadata management.
• TIndex:Create() opens the DBF, executes the INDEX command, and closes the file. It supports both CDX (default) and NTX formats based on the cType member.

See Also

• Classes Alphabetical
• Functions