HeapAlloc/Free/Size problems

[mark smit]

Hello all,


I was just wondering why HeapSize returns (-1/FFFFFFFF). This indicates
that the function failed but I can't figure out why?

#compile exe
#include "win32api.inc"


function pbmain as long
    dim lookup  as long ptr
    dim lsize   as long
    
    
    lookup = HeapAlloc(GetProcessHeap,%HEAP_GENERATE_EXCEPTIONS,1024)
    lsize = HeapSize(GetProcessHeap,0,lookup)
    
    
    msgbox format$(GetProcessHeap)
    
    
    msgbox format$(lookup) & $CRLF & hex$(lsize)
    
    lookup = HeapFree(GetProcessHeap,0,lookup)
    lsize = HeapSize(GetProcessHeap,0,lookup)
    
    msgbox format$(lookup) & $CRLF & hex$(lsize)
end function

Thanks for any help!

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Cheers

[Jim Huguley]

Mark..

Call HeapSize third parameter with Byval since the third parameter
of HeapSize in the Win32API is defined "as ANY"..

#COMPILE EXE
#INCLUDE "win32api.inc"

FUNCTION PBMAIN AS LONG
    LOCAL lHeapPtr AS LONG
    LOCAL lsize    AS DWORD

    lHeapPtr = HeapAlloc(GetProcessHeap,%HEAP_GENERATE_EXCEPTIONS,1024)
    lsize = HeapSize(GetProcessHeap, 0, BYVAL lHeapPtr)

    MSGBOX FORMAT$(lHeapPtr) & $CRLF & FORMAT$(lsize) & $CRLF & "&h" & HEX$(lsize)

    lHeapPtr = HeapFree(GetProcessHeap,0,lHeapPtr)
    lsize = HeapSize(GetProcessHeap, 0, BYVAL lHeapPtr)

    MSGBOX FORMAT$(lHeapPtr) & $CRLF & HEX$(lsize) & $CRLF & "&h" & HEX$(lsize)
END FUNCTION

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Jim..
[email protected]

[mark smit]

Thanks!

I'm also having a hard time understanding how the Global and Local
memory functions work. I know they must call the Heap functions
but I dont see how you can set the %GMEM_MOVABLE and %GMEM_FIXED
properties with the Heap functions. Do the Global and Local functions
use the Heap functions at a lower level?

Also, when you use Heap functions to allocate memory does the pointer
returned stay valid throughout the life of the allocated block or
does the block move around and thus invalidate the pointer?




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Cheers

[Jim Huguley]

Mark..

1. The GlobalAlloc is only maintained for backward compatibility with
16 bit code. It is recommended that you use the newer heap function.
So, I would assume unless you have a compeling reason to use
GlobalAlloc with the GMEM_? constants you move on to them.

2. According to MSDN, the memory is not movable. The pointer is
valid until you de-allocate the memory. Of course you will have
to maintain the pointer in a manner within the scope of your usage
(i.e. sub/function/global/etc..)

3. There are some thread issues if your program is multi-threaded
that you should read about in the Remarks on MSDN under HeapFree
and HeapAlloc.



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Jim..
[email protected]

[Florent Heyworth]

Hi Mark

just a tip: I noticed that you are using HEAP_GENERATE_EXCEPTIONS when
calling HeapAlloc; you should only use this if you really want to
display a GPF message box to your users in the case that the HeapAlloc function
fails (out of memory, or..)

The HEAP_GENERATE_EXCEPTIONS modifier, is in general only called
by applications which use SEH (Structured Exception Handling). I'd avise
you not to use this flag. Use 0& or HEAP_ZERO_MEMORY to initialize
memory or HEAP_NO_SERIALIZE in single threaded applications.

That way if HeapAlloc fails it'll simply return NULL instead of
an exception.

Cheers

Florent

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[mark smit]

Thanks Florent!

I only did that because I wanted some sort of notification if
there was an error of any kind.

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Cheers