Print Page - Structs, and Procs

Title: Structs, and Procs
Post by: Artoo on February 21, 2005, 09:14:56 AM

Heres another dumb question for you all, say I have the follow:

MyObj struct
	m_fpSetWindowLong  DWORD  NULL
MyObj ends

MyObjPTR TYPEDEF PTR MyObj 

MyProc proto :ObjPTR

MyProc proc pData:ObjPTR
    MOV  EAX, pData.m_fpSetWindowLong
MyProc endp

Why does the the assembler give me the following error on the MOV line:
error A2006: undefined symbol : m_fpSetWindowLong

Also, what would I have to do to use invoke to call SetwindowLong? eg

Code Select

invoke pData.m_fpSetWindowLong, 0,0,0

Thanks for any help.....

Title: Re: Structs, and Procs
Post by: Jibz on February 21, 2005, 09:27:45 AM

Code Select

MyObjPTR TYPEDEF PTR MyObj

MyProc proto :ObjPTR

You used ObjPTR instead of MyObjPTR.

Regarding using invoke indirectly, check this thread (http://www.masmforum.com/simple/index.php?topic=694.0).

Title: Re: Structs, and Procs
Post by: Artoo on February 21, 2005, 09:35:04 AM

Oops sorry Jibz, that was just a typo. I still get the same error message?

Title: Re: Structs, and Procs
Post by: Jibz on February 21, 2005, 09:59:10 AM

That's because it's a double indirection. The mov instruction would have to first load the pointer from the stack, and then load the struct member from the struct it points to. You have to first get the pointer, and then use it to access the memory:

Code Select

    MOV    EDX, pData
    MOV    EAX, [MyObjPTR PTR EDX].m_fpSetWindowLong

or you can use ASSUME if you have multiple accesses throughout the function and keep the struct pointer in the same register:

Code Select

    MOV    EDX, pData
    ASSUME EDX:MyObjPTR
    MOV    EAX, [EDX].m_fpSetWindowLong
    ...
    ASSUME EDX:NOTHING

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General Forums => The Campus => Topic started by: Artoo on February 21, 2005, 09:14:56 AM