Dec 102017
 
Various C Functions For Clipper - Good UDF Examples.
File CLIPC.ZIP from The Programmer’s Corner in
Category Dbase Source Code
Various C Functions For Clipper – Good UDF Examples.
File Name File Size Zip Size Zip Type
ALPHN.C 2031 884 deflated
ALPHN.PRG 1252 473 deflated
CLIP_C.DOC 2230 1069 deflated
CLIP_C.H 3935 1307 deflated
TURBOC.CFG 169 104 deflated
UP.PRG 1861 713 deflated

Download File CLIPC.ZIP Here

Contents of the CLIP_C.DOC file


Overview:

The function AlphaN is a good example of a Clipper UDF written in C. It
also shows how to use _exmgrab and _exmback, the EXTEND system's memory
allocation routines.

Included is my version of EXTEND.H and NANDEF.H, CLIP_C.H, I hope
Nantucket doesn't mind. (Note to Nantucket: CLIP_C.H is a modified
version of your EXTEND.H and NANDEF.H, if you would like to use
any or all of my modifications, feel free.)

Initially, I wrote AlphaN in dbase (AlphN.prg). Then I rewrote it in C
(AlphN.c). For a C compiler, I used Turbo C (tm), v 1.5 from Borland,
though I suspect others will work too (?). Also, you shouldn't have any
difficulties using Turbo C 1.0. For a dbase compiler, I used Clipper
(tm), Summer '87 from Nantucket.

Extend's memory allocation: _exmgrab and _exmback

These two functions are a much appreciated addition to Clipper's
EXTEND system. They are similar to the malloc and free functions
in C, which cannot be used in a Clipper UDF.

You need to be aware of two things to use these functions successfully:
1) any memory _exmgrab.ed must be _exmback.ed in the same UDF
2) you must be sure to pass the correct size when _exmback.ing (free
doesn't require this)

At first glance, these two functions may seem useless; i.e., it would
appear that you couldn't pass a string back to Clipper since you can't
keep the memory allocated. However, the _retxx takes care of this by
allocating its own memory and copying the string into it. You take
the following steps to return a string:
1) _exmgrab memory
2) construct string
3) _retxx it
4) _exmback memory


Compilation of C UDF

AlphN.c was compiled using the command line version of Turbo C with
the configuration file TURBOC.CFG available in the current directory.
This configuration file sets up TC to compile in large model and
forces the segment names to Clipper segment names and some other
stuff (see EXTEND.DOC on your Clipper disks)


Questions, comments, suggestions.

Please send any Q,C or S to:

Mark Pfeifer
Source ID: BFB511
Compuserve: 73657,3203


 December 10, 2017  Add comments

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