ASM Community

G'day All,

I am trying to use the Expat XML parser from within my ASM Win32
application.

I have built a library "lib" file as per Iczelion's "How toCreate your
own MASM Import Libraries" instructions. I can load the library and call
some expat functions without error:

  invoke XML_ParserCreate, 0

  ...

  invoke XML_SetElementHandler, hXMLParser, funStart, funEnd

  ...

However when I call "XML_Parse", the program crashes:

  invoke XML_Parse, hXMLParser, buff, 21, 0	; BANG

So I tried to load the "libexpat.dll" dynamically, with much the
same result:

.data

	...

	; Dynamically load the DLL

	; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	MyDLLName					db "libexpat.dll",0

	XMLParse						db "XML_Parse",0

	XMLParserCreate			db "XML_ParserCreate",0

	XMLSetElementHandler		db "XML_SetElementHandler",0

	...

	hMyDLL						dd ?

	addrParse					dd ?

	addrParserCreate			dd ?

	addrSetElementHandler	dd ?

	...



	; Expat XML processing callback functions

	fStart						db 'funStart',0

	fEnd							db 'funEnd',0



	buff							db '<action> id </action>',0



.code



start:

	...



	; Dynamically load the DLL

	; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	invoke LoadLibrary, OFFSET MyDLLName

	mov [hMyDLL], eax



	; XML_ParserCreate

		invoke GetProcAddress, [hMyDLL], offset XMLParserCreate

		.if(eax == NULL)

			invoke Beep, 1000, 100

		.endif

		mov	[addrParserCreate], eax

		; p = XML_ParserCreate(NULL); 

		push 	NULL               ; dword1

		call	[addrParserCreate]

		mov hXMLParser, eax



	; XML_SetElementHandler

		invoke GetProcAddress, [hMyDLL], offset XMLSetElementHandler

		.if(eax == NULL)

			invoke Beep, 1000, 100

		.endif

		mov	[addrSetElementHandler], eax

		; XML_SetElementHandler(p, start, end);

		push	offset fEnd       ; dword3

		push	offset fStart     ; dword2

		push	[hXMLParser]   ; dword1

		call	[addrSetElementHandler]



	; XML_Parse [CRASH]

	invoke GetProcAddress, [hMyDLL], offset XMLParse

		.if(eax == NULL)

			invoke Beep, 1000, 100

		.endif

		mov	[addrParse], eax

		; XML_Parse(XML_Parser p, const char *s, int len, int isFinal)

		push	0                     ; dword4

		push	21                   ; dword3

		push	offset buff        ; dword2

		push	[hXMLParser]    ; dword1

		call	[addrParse]        ; BANG

Does anyone know what I have done wrong, and why the XMLParse function
crashes my application. I have also tried the LibXML XML C parser with
no luck :(


Links:
Expat XML Parser http://www.libexpat.org
LibXML XML C parser http://www.xmlsoft.org/

Also:
I am fairly new to ASM amd Win32 programming


Thanks

Dorf

G'day f0dder,

Thanks for the quick response

That helped. The app still crashes however.


The parser now calls my start function and pops a message box
with the opening tag "<action>". :)

But it crashes before calling the end function :(

; start(void *data, const char *el, const char **attr)

funStart proc	data:DWORD, el:DWORD, attr:DWORD

	;invoke Beep, 1000, 100	; Bell

	invoke	MessageBox, NULL, el, NULL, MB_OK

	ret

funStart endp



; end(void *data, const char *el) {

funEnd proc	data:DWORD, el:DWORD

	invoke Beep, 100, 100	; Bell

	ret

funEnd endp

Thanks for your help
Dorf

G'day f0dder,

Yep ... that seems to have done the trick :)

Just for the record, I had to now define the start/end function
prototypes as:

funStart         proto C :DWORD, :DWORD, :DWORD

funEnd           proto C :DWORD, :DWORD

Now I can start testing the expat parser :-D

Thank you very much

I think Win32Asm is very cool

Thanks again
Dorf

Looking at the C code attr seems to be a pointer to an array of pointers to strings so you could try for example this code which should mimic the "for" loop given. I haven't tested this though :)

;Loop through attrs

mov ecx,attr	; ecx point to attr array

cmp [ecx],0	; test ecx for NULL

jz endLoop

startLoop:

	mov eax,[ecx]	; eax points to string



	; ... do something here ...



	; move ecx onto next string and recheck for NULL

	add ecx,4

	cmp [ecx],0

	jnz startLoop

endLooop:

Basically if a memory variable is a pointer to a point then the following will get you to the "thing"

mov eax,attr	; eax is pointer to pointer

mov eax,[eax]	; eax is pointer

mov eax,[eax]	; eax is the "thing"

For strings though you wont need the last mov cause you'll be dealing with their pointers anyway.

Just thinking it might be important to also check ecx for NULL ie

;Loop through attrs

mov ecx,attr   ; ecx point to attr array

cmp ecx,0  ; <-- check if attr is null

jz endLoop

cmp [ecx],0   ; test ecx for NULL

jz endLoop

startLoop:

G'day All,

Here is my little demo of using the Expat XML parser in an
RadASM/MASM project.

This application parses an XML file into a Treeview control.
See the included "Readme.txt" for a more detailed description.

I've also included a project to create the import library
for the Expat XML parser C library.

Issues:
After reading the XML file into a string buffer, I cannot get
the actual length of the XML contents (with sizeof buff).
If I pass this buffer to Expat, it complains about malformed
document, or something.

As a workaround I get the size of the XML file:
invoke GetFileSizeFile, fileName
and pass this return value (eax) to Expat.
invoke XML_Parse, hXMLParser, addr buff, eax, 0
and Expat seems happy with this.

Someone that knows what they're doing may be able to figure this
out ... perhaps!


Use this at your own risk - I am fairly new to ASM/Win32 :)

Thanks for the help

ASM/Win32 rocks.

dorf

dorf:

  Hello, I could not find the demo you mentioned. Will you please check the link?

  Thank you.