im trying to use this from c++ in masm32:
lpBits = (LPBYTE) GlobalAlloc(GMEM_FIXED, pbih->biSizeImage);
so far i got this:
push 100
push GMEM_FIXED
call dword ptr [GlobalAlloc]
mov lpBits,eax
it assembles fine, but...
it crashes the program...
any idea what's wrong?
i used a disassembly of another prog to see how this might work
Not the solution to your problem, but why not simplify things? Use this instead of "push-push-call":
INVOKE GlobalAlloc, GMEM_FIXED, 100
Also, are you sure you want to use GlobalAlloc() and not some other memory-allocation function? Micro$oft has this to say about it:
QuoteNew applications should use the heap functions to allocate and manage memory unless the documentation specifically states that a global function should be used. For example, the global functions are still used with Dynamic Data Exchange (DDE), the clipboard functions, and OLE data objects.
Still, it looks like what you wrote should work ... [edits after JJ's reply] ... ASSUMING 1) 100 bytes is enough to hold whatever you're trying to put in there, and 2) not sure why you used the construct
[GlobalAlloc] rather than just the function name.
Anyhow, what JJ said ...
Hi dc,
As NoCforMe already pointed out, a simple invoke GlobalAlloc, GMEM_FIXED, 100 will do the job. However, I have a little doubt whether 100 bytes are enough for an image. Is that really the size?
You should zip your complete source and executable and attach it to the next post, so that we can help you better.
Hi dc
The reason your code crashes is becouse you are trying to dereference the
address of the GlobalAlloc function by doing this
call dword ptr [GlobalAlloc]
Just call it the proper way
call GlobalAlloc
im trying to save a bitmap that was created with CreateCompatibleBitmap
im getting the snippet here:
https://learn.microsoft.com/en-us/windows/win32/gdi/storing-an-image (https://learn.microsoft.com/en-us/windows/win32/gdi/storing-an-image)
it's not large enough just simplified for experimenting
in the example they seem to get a pointer instead of a handle and it's got me stumped
i got this from dissassembling some other app:
00409382 8B4608 mov eax,[esi+8]
00409385 C1E004 shl eax,4
00409388 83C008 add eax,8
0040938B 50 push eax
0040938C 6A02 push 2
0040938E FF151CF24D00 call dword ptr [GlobalAlloc]
i cant get a handle to work like a pointer when i just invoke it
Hi dc,
Here is a small command-line tool saving your desktop as a bitmap file, maybe it can be useful for you :
SaveDesktop.exe MyDesktop.bmp
SaveDesktop.exe MyDesktop2.bmp 32
The second option saving the bitmap as 32-bit
Edit : It's easier to study the official documentation than trying to figure out disassembled code :
https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-globalalloc
As @Caché GB pointed out, don't try to dereference the function pointer.
And don't just plop debugger-displayed code in your source. Apples and oranges. This won't work:
0040938E FF151CF24D00 call dword ptr [GlobalAlloc]
As @Caché GB stated, just use
CALL GlobalAlloc
Or better yet just use INVOKE GlobalAlloc ...
Quote from: dc on September 01, 2023, 06:42:34 AMi cant get a handle to work like a pointer when i just invoke it
Sounds like you're learning a very important lesson for Win32 programming:
the difference between a handle and a pointer.
Let's take memory allocation using the heap functions:
- To start, you need to use GetProcessHeap() to get a handle to the heap.
- To actually allocate memory using this handle, use HeapAlloc(), which returns a pointer to the allocated memory.
This is just one example (though I would highly recommend that you use the heap-allocation stuff rather than
GlobalAlloc(), even though that one MS example used it). If you read the Microsoft (or other) documentation carefully, it'll tell you whether you're getting a handle or a pointer back. As you're discovering, the two are not interchangeable! A handle will never "work like a pointer", and vice versa.
(Ackshooly, hopefully not to confuse you, but a handle
is a pointer, except that it points to some internal data structure inside Windows that we, as programmers, really aren't supposed to know about nor mess with. So it's not a pointer in the sense that you can use it to access, say, an array of data (bytes/words/dwords, whatever). So don't get the two mixed up!)
thanx guys, ill try this stuff out...
i get 0 from GetDIBits() and last error says it succeeded...
i think i should get return of 1080...
savepic proc
local bmp:BITMAP
local bmi:BITMAPINFO
local pbmi:PTR BITMAPINFO
local pclrs:DWORD
local prgb:DWORD
local cClrBits:WORD
local hf:HANDLE
local hdr:BITMAPFILEHEADER
local pbih:PBITMAPINFOHEADER
local lpBits:LPBYTE
local dwTotal:DWORD
local cb:DWORD
local php:PTR BYTE
local dwTmp:DWORD
local pbi:PTR BITMAPINFO
local hheap:HANDLE
local pbmp:PTR BITMAP
lea eax,bmp
mov pbmp,eax
vk BeginPaint,hwnd,addr ps
mov hdc,eax
vk CreateCompatibleDC,hdc
mov hdct,eax
vk SelectObject,hdct,hbmpt
; CreateBitmapInfoStruct
mov esi,pbmp
ASSUME esi:ptr BITMAP
vk GetObject,hbmpt,sizeof BITMAP,esi ; get color format & dims
mov cClrBits,24
m2m bmi.bmiHeader.biSize,sizeof BITMAPINFOHEADER
vk GetProcessHeap
mov hheap,eax
vk HeapAlloc,hheap,HEAP_NO_SERIALIZE,sizeof BITMAPINFO
mov pbmi,eax
mov esi,eax
ASSUME esi:ptr BITMAPINFO
m2m [esi].bmiHeader.biWidth,bmp.bmWidth
m2m [esi].bmiHeader.biHeight,bmp.bmHeight
m2m [esi].bmiHeader.biPlanes,bmp.bmPlanes
m2m [esi].bmiHeader.biBitCount,bmp.bmBitsPixel
m2m [esi].bmiHeader.biClrUsed,eax
mov [esi].bmiHeader.biCompression,BI_RGB
mov eax,[esi].bmiHeader.biWidth
add eax,7
divid 8
mult [esi].bmiHeader.biHeight
xor ecx,ecx
mov cx,cClrBits
xor edx,edx
mul ecx
mov [esi].bmiHeader.biSizeImage,eax
; CreateBMPFile
vk HeapAlloc,hheap,HEAP_NO_SERIALIZE,[esi].bmiHeader.biSizeImage
mov lpBits,eax
ASSUME eax:ptr LPBYTE
vk GetDIBits,hdct,hbmpt,0,[esi].bmiHeader.biHeight,lpBits,pbmi,DIB_RGB_COLORS
vk HeapFree,hheap,HEAP_NO_SERIALIZE,lpBits
vk HeapFree,hheap,HEAP_NO_SERIALIZE,pbmi
vk HeapDestroy,hheap
vk DeleteDC,hdc
vk DeleteDC,hdct
vk EndPaint,hwnd,addr ps
Ret
savepic EndP
RESOLVED... a line was oout of place... oops
NOPE... NOT RESOLVED...
still getting return 0
Quote from: NoCforMe on September 01, 2023, 06:57:57 AM(Ackshooly, hopefully not to confuse you, but a handle is a pointer, except that it points to some internal data structure inside Windows that we, as programmers, really aren't supposed to know about nor mess with. So it's not a pointer in the sense that you can use it to access, say, an array of data (bytes/words/dwords, whatever). So don't get the two mixed up!)
GlobalAlloc is a special case here:
invoke GlobalAlloc, GMEM_FIXED, 100 ; eax is a pointer to the memory block
mov ptr1, eax
invoke GlobalAlloc, GMEM_MOVEABLE, 100 ; eax is a handle to a memory object
mov handle, eax
invoke GlobalLock, handle ; To translate the handle into a pointer, use GlobalLock
mov ptr2, eax
; ... do useful things with ptr2 ...
invoke GlobalUnlock, handle ; release the pointer (but not the memory object)
invoke GlobalFree, handle ; release the memory object
invoke GlobalFree, ptr1 ; release the memory objectWhen monitoring the handle and the pointers, you would typically get something like this:
handle 3538948
ptr1 6608584
ptr2 6608712Handle and pointers sit in different memory areas.
For 90% of all uses, GMEM_FIXED does the job: you get a pointer directly. The exceptions are the clipboard, DDE, and OLE objects (https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-globalalloc):
QuoteNew applications should use the heap functions to allocate and manage memory unless the documentation specifically states that a global function should be used. For example, the global functions are still used with Dynamic Data Exchange (DDE), the clipboard functions, and OLE data objects.
thanx... funny how it can be so difficult to get info like that...
have a funny day
Quote from: dc on September 01, 2023, 10:31:12 PMthanx... funny how it can be so difficult to get info like that...
Au contraire, my friend: learn.microsoft.com (https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-globalalloc) is your friend. All the info you need is there.
Well, there and also Stack Overflow, Code Project, etc. (You might want to look at Raymond Chen's excellent blog, The Old New Thing (https://devblogs.microsoft.com/oldnewthing/).)