Q181289

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page	Q181289: HOWTO: Pass Structures to a DLL	/kb/181/Q181289/

Q181289: HOWTO: Pass Structures to a DLL

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Article: Q181289
Product(s): Microsoft FoxPro
Version(s): 
Operating System(s): 
Keyword(s): kbcode kbnokeyword kbvfp300 kbvfp500 kbvfp600
Last Modified: 06-AUG-1999

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

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

SUMMARY
=======

Many DLLs require that the calling program pass a structure. FoxPro can pass by
reference a string of the same length as the required structure. Depending on
the datatype, some variables need to be converted to the proper format. For
instance, DWORD is a low-high format, so any 4-byte values need to be converted
to a string in the DWORD format. DLLs may also return values that need to be
converted from a string in a low-high format to an integer value.

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

The Win32 API function GetSystemInfo requires that a pointer to a structure be
passed to the function. The following example demonstrates how to make the call
then convert the elements of the returned string using the StrToLong function.
The LongToStr function to do the reverse is also included.

Copy this code into a program file (.prg) and run the program. This program uses
GetSystemInfo to return information about a computer's processor and memory.

The code is listed below:

     #DEFINE CR CHR(13)
     #DEFINE PROCESSOR_INTEL_386 386
     #DEFINE PROCESSOR_INTEL_486 486
     #DEFINE PROCESSOR_INTEL_PENTIUM 586
     #DEFINE PROCESSOR_MIPS_R4000 4000
     #DEFINE PROCESSOR_ALPHA_21064 21064

     DECLARE GetSystemInfo IN win32api STRING @SystemInfo
     DECLARE GlobalMemoryStatus IN win32api STRING @MemStat
     SystemInfo = SPACE(36)
     m.stru = LongToStr(32) + REPLICATE(CHR(0), 28)
     =GetSystemInfo(@SystemInfo)
     =GlobalMemoryStatus(@m.stru)
     m.oem_id = StrToLong(LEFT(SystemInfo, 4))
     m.page_size = StrToLong(SUBSTR(SystemInfo, 5, 4))
     m.minappaddr = StrToLong(SUBSTR(SystemInfo, 9, 4))
     m.maxappaddr = StrToLong(SUBSTR(SystemInfo, 13, 4))
     m.processormask = StrToLong(SUBSTR(SystemInfo, 17, 4))
     m.num_processors = StrToLong(SUBSTR(SystemInfo, 21, 4))
     m.processortype = StrToLong(SUBSTR(SystemInfo, 25, 4))
     m.processorname = ""
     m.memoryload = StrToLong(SUBSTR(m.stru, 5, 4))
     m.totalphys = StrToLong(SUBSTR(m.stru, 9, 4))
     m.availphys = StrToLong(SUBSTR(m.stru, 13, 4))
     m.totalpagefile = StrToLong(SUBSTR(m.stru, 17, 4))
     m.availpagefile = StrToLong(SUBSTR(m.stru, 21, 4))
     m.totalvirtual = StrToLong(SUBSTR(m.stru, 25, 4))
     m.availvirtual = StrToLong(SUBSTR(m.stru, 29, 4))
     DO CASE
     CASE m.processortype = PROCESSOR_INTEL_386
        m.processorname = "INTEL 386"
     CASE m.processortype = PROCESSOR_INTEL_486
        m.processorname = "INTEL 486"
     CASE m.processortype = PROCESSOR_INTEL_PENTIUM
        m.processorname = "INTEL Pentium"
     CASE m.processortype = PROCESSOR_MIPS_R4000
        m.processorname = "MIPS R4000"
     CASE m.processortype = PROCESSOR_ALPHA_21064
        m.processorname = "ALPHA 21064"
     ENDCASE
     m.allocationgranularity = StrToLong(SUBSTR(SystemInfo, 29, 4))
     m.reserved = StrToLong(SUBSTR(SystemInfo, 33, 4))
     =MESSAGEBOX("OEM ID:" + STR(m.oem_id) + CR + ;
      "Page Size: " + STR(m.page_size) + CR + ;
      "Minimum application address: " + STR(m.minappaddr) + CR +;
      "Maximum application address: " + STR(m.maxappaddr) + CR + ;
      "Processor mask: " + STR(m.processormask) + CR + ;
      "Number of processors: " + STR(m.num_processors) + CR + ;
      "Allocation granularity: " + STR(m.allocationgranularity) + CR + ;
      "Percent memory in use: " + STR(m.memoryload) + CR + ;
      "Bytes of physical memory present: " + STR(m.totalphys) + CR + ;
      "Bytes available physical memory: " + STR(m.availphys) + CR + ;
      "Bytes of paging file: " + STR(m.totalpagefile) + CR + ;
      "Bytes available paging file: " + STR(m.availpagefile) + CR + ;
      "Total virtual memory: " + STR(m.totalvirtual) + CR + ;
      "Available bytes virtual memory: " + STR(m.availvirtual),0+64+0)

     *-- The following function converts a long integer to an ASCII
     *-- character representation of the passed value in low-high format.
     ******************
     FUNCTION LongToStr
     ******************
     * Passed : 32-bit non-negative numeric value (lnLongval)
     * Returns : ascii character representation of passed value in low-high
     * format (lcRetstr)
     * Example :
     *   m.long = "999999"
     *   m.longstr = long2str(m.long)

     PARAMETERS lnLongval

     PRIVATE i, lcRetstr

     lcRetstr = ""
     FOR i = 24 TO 0 STEP -8
        lcRetstr = CHR(INT(lnLongval/(2^i))) + lcRetstr
        lnLongval = MOD(lnLongval, (2^i))
     NEXT
     RETURN lcRetstr

     *-- The following function converts a string in low-high format to a
     *-- long integer.
     ******************
     FUNCTION StrToLong
     ******************
     * Passed:  4-byte character string (lcLongstr) in low-high ASCII format
     * Returns:  long integer value
     * Example:
     * m.longstr = "1111"
     * m.longval = str2long(m.longstr)

     PARAMETERS lcLongstr

     PRIVATE i, lnRetval

     lnRetval = 0
     FOR i = 0 TO 24 STEP 8
        lnRetval = lnRetval + (ASC(lcLongstr) * (2^i))
        lcLongstr = RIGHT(lcLongstr, LEN(lcLongstr) - 1)
     NEXT

     RETURN lnRetval

Additional query words:

======================================================================
Keywords          : kbcode kbnokeyword kbvfp300 kbvfp500 kbvfp600 
Technology        : kbVFPsearch kbAudDeveloper kbVFP300 kbVFP300b kbVFP500 kbVFP600 kbVFP500a
Issue type        : kbhowto

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