Q216055: HOWTO: Pass an Array by Reference to LCK and Return Changes

Article: Q216055
Product(s): Microsoft FoxPro
Version(s): WINDOWS:3.0b,5.0a,6.0
Operating System(s): 
Keyword(s): kbVC kbvfp300b kbvfp500a kbvfp600 kbXBase
Last Modified: 17-FEB-1999

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The information in this article applies to:

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

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