DOCUMENT:Q216055  17-FEB-1999  [foxpro]
TITLE   :HOWTO: Pass an Array by Reference to LCK and Return Changes
PRODUCT :Microsoft FoxPro
PROD/VER:WINDOWS:3.0b,5.0a,6.0
OPER/SYS:
KEYWORDS:kbVC kbvfp300b kbvfp500a kbvfp600 kbXBase

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Visual FoxPro for Windows, versions 3.0b, 5.0a, 6.0 
-------------------------------------------------------------------------------

SUMMARY
=======

This article demonstrates how to pass an array of real numbers to a FoxPro
Library Construction Kit (LCK) routine in Visual C, manipulate the array in the
LCK routine, and return the changed array to Visual FoxPro.

MORE INFORMATION
================

Create a Visual FoxPro FLL in Visual C++ using the following C code:

   #include <windows.h>
   #include <pro_ext.h>

   void FAR ByRef_array(ParamBlk FAR *parm)
   {
      int     start;         /* Starting value of Loop. */ 
      Value   val;           /* Create Value structure. */ 
      Locator loc;           /* Create Locator structure. */ 

      start=0;
      loc = parm->p[0].loc;  /* Store the contents of the FoxPro array
                                     in the Locator structure. */ 

      /* Get the number of elements from the FoxPro array. */ 

      loc.l_subs = (int)_ALen(parm->p[0].loc.l_NTI, AL_ELEMENTS);

      /* FOR loop to get the array elements. */ 

      for(start=0;start != loc.l_subs ; start ++){
         loc.l_sub1=(start+1);

         /* Store the contents of the FoxPro array in a Value Structure.*/ 
         _Load(&loc,&val);

         /* Copy the contents of the FoxPro array to the function array.*/ 
   		
         /* Test array contents and manipulate accordingly */ 
         if (val.ev_type == 'N') 
            {
            if (val.ev_real < 10) 
               val.ev_real = val.ev_real * 1;
            else 
               if (val.ev_real < 20) 
                  val.ev_real = val.ev_real * 2;
               else 
                  if (val.ev_real < 30)
                     val.ev_real = val.ev_real * 3;
                  else val.ev_real = val.ev_real * 4;	
         }
         else
            MessageBox(NULL,"Wrong Data type","Should be a number.",MB_OK);
   		
         /* Copy the contents of Locator Structure into Value Structure.*/ 
         _Store(&loc, &val); 	 
   		   
      }		
   }

      FoxInfo myFoxInfo[]={
         {"ByRef_ARRAY",(FPFI)ByRef_array,1,"R"},
      };

      FoxTable _FoxTable={
         (FoxTable FAR*)0, sizeof(myFoxInfo) / sizeof(FoxInfo), myFoxInfo
      };

To test that the array has changed, create a program and enter the following
FoxPro code:

   CLEAR
   cfixed=SET('FIXED')
   SET FIXED ON

   cdecimal=SET('DECIMALS')
   SET DECIMAL TO 4

   * Point to the DLL built in Visual C 
   SET LIBRARY TO "D:\visual c 6\MyProjects\by_ref\Debug\by_ref.dll"

   * Populate array with random values then print to see original values
   PUBLIC by_reftest(10)

   ?"Array before LCK routine..."
   FOR i = 1 TO ALEN(by_reftest)
   	by_reftest(i)= 60 * RAND()
   	?by_reftest(i)
   ENDFOR

   * Call the LCK function and pass the array by reference
   =ByRef_array(@by_reftest)

   ?"Array after LCK routine..."
   FOR i = 1 TO ALEN(by_reftest)
      ?by_reftest(i)
   ENDFOR

   SET FIXED &cfixed
   SET DECIMALS TO &cdecimals
   SET LIBRARY TO

REFERENCES
==========

For additional information about the FoxPro Library Construction Kit (LCK),
please see the following articles in the Microsoft Knowledge Base:

Q122591 PRB: How to Change Variable Value Passed by Reference in LCK

Q119636 How to Pass an Array to a Routine in an LCK Library

(c) Microsoft Corporation 1999, All Rights Reserved. Contributions by Dean
Christopher, Microsoft Corporation.


Additional query words:

======================================================================
Keywords          : kbVC kbvfp300b kbvfp500a kbvfp600 kbXBase 
Technology        : kbVFPsearch kbAudDeveloper kbVFP300b kbVFP600 kbVFP500a
Version           : WINDOWS:3.0b,5.0a,6.0
Issue type        : kbhowto

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1999.