Checking for the existence of an ISAM-emulated index using PGDBE

[Pat France]

Background​

Clipper programmers have traditionally used the File() function for verifying whether a given index exists. When running under the ISAM emulation of the PGDBE, however, this approach can no longer be used because ISAM-emulated indexes are not maintained as separate files.

Checking for the existence of an ISAM-emulated index​

The easiest way to check for the existence of an index is by just trying to open it. The following code illustrates this approach.

USE customer
IF .NOT. IndexExists("custa.ntx")
   OrdCreate( "custa.ntx", "custno" )
ENDIF
...


// Check whether an index exists by attempting to open it. A suitable table must be open in the current
// work area
FUNCTION IndexExists( cIndex )
 LOCAL bOld

  bOld := ErrorBlock( {|e| Break(e)} )
  BEGIN SEQUENCE
    OrdListAdd( cIndex )
  RECOVER
     ErrorBlock( bOld )
     RETURN .F.
  END SEQUENCE
  ErrorBlock( bOld )

  OrdListClear()
RETURN .T.