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Q139070: PRB: Stack Violation Calling 16-Bit DLL with FoxTools

Article: Q139070
Product(s): Microsoft FoxPro
Version(s): WINDOWS:3.0
Operating System(s): 
Keyword(s): 
Last Modified: 11-FEB-2000

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 3.0 
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SYMPTOMS
========

Using the FOXTOOLS CallFn()function to call a 16-bit DLL and passing a "L" as an
argument generates the error "Stack Violation. Please check the parameters." The
same function call works well with FoxPro for Windows versions 2.x.

CAUSE
=====

The function is registered and called as follows.

     Int_num=regfn("Fn_init","L","I", "<path to DLL>")
     Int_ret=callfn(int_num,0)

In this call, the "L" parameter, which represents a long argument, is passed to
the DLL. The API function expects a short argument, and the stack allocated for
the parameter is filled. The "S" argument, which represents a short integer,
should be passed instead.

In the version of Foxtools shipped with FoxPro versions 2.x for Windows the "S"
argument was not valid. Additionally, the version of Foxtools.fll shipped with
Visual FoxPro version 3.0 checks parameters more strictly than previous
versions.

RESOLUTION
==========

When registering a function from a 16-bit DLL, pass an "S" instead of an "L" as
in this example:

     Int_num=regfn("Fn_init","S","I", "<path to DLL>")
     Int_ret=callfn(int_num,0)

For more information about Foxtools.fll and the syntax you can use, please see
the Foxtools.hlp file located in the Vfp\Tools directory.

STATUS
======

This behavior is by design.

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

Steps to Reproduce Behavior
---------------------------

The following example program duplicates the error. To correct it, change the "L"
parameter to "S".

     SET LIBRARY TO HOME()+"FOXTOOLS.FLL"            && Locates Foxtools
     hhand=REGFN("WinHelp","ICIC","I")
     LPZFILENAME=HOME()+"FOXHELP.HLP"+CHR(0)
     WCOMMAND=258
     DWDATA="SEARCH()"+CHR(0)
     MYCALL=MAINHWND()
     HELP
     =CALLFN(hhand,MYCALL,LPZFILENAME,WCOMMAND,DWDATA)
     RELEASE HHAND
     SET LIBRARY TO      && Releases Foxtools

Additional query words:

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Keywords          :  
Technology        : kbVFPsearch kbAudDeveloper kbVFP300
Version           : WINDOWS:3.0

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