Print Page - A function that accepts a function pointer

Title: A function that accepts a function pointer
Post by: bf2 on October 13, 2011, 12:57:22 PM

It's a generic question, but how do I create a function in MASM that accepts a function pointer?

I have searched a few books (including Irvine and Pirogov) and couldn't find anything on this.

I have searched the forum and found some discussions on how to call a function using a pointer, but not how to write a function that expects a function pointer - like you do in C.

Thanks in advance.

Title: Re: A function that accepts a function pointer
Post by: dedndave on October 13, 2011, 01:11:30 PM

Code Select

FuncProc PROTO :DWORD
Func     PROTO

;

        .CODE

FuncProc PROC lpfnProc:DWORD

        call dword ptr lpfnProc
        ret

FuncProc ENDP

Func    PROC

        ret

Func    ENDP

;to call it

        INVOKE  FuncProc,Func

Title: Re: A function that accepts a function pointer
Post by: ToutEnMasm on October 13, 2011, 01:16:37 PM

Perhaps more explains ( a sample for example) could be useful.
Here is some samples

Monproc proc
...
Monproc endp

.data
pointer dd Monproc ;put the adress of Monproc in pointer
.code
invoke afunction,parm1,Monproc ;pass the adress of Monproc to afunction

Title: Re: A function that accepts a function pointer
Post by: qWord on October 13, 2011, 01:22:23 PM

If you want to use INVOKE, a typedef is needed:

Code Select

MYMSG typedef proto hWnd:HWND,psz1:PCHAR,psz2:PCHAR,flg:DWORD
PMYMSG typedef ptr MYMSG

myMsg proc hWnd:HWND,psz1:PCHAR,psz2:PCHAR,flg:DWORD

	invoke MessageBox,hWnd,psz1,psz2,flg
	ret
	
myMsg endp

xyz proc pFnc:PMYMSG

	invoke pFnc,0,0,0,0
	; or:  invoke PMYMSG ptr ...,0,0,0,0
	ret
xyz endp
...
invoke xyz,myMsg

Title: Re: A function that accepts a function pointer
Post by: Farabi on October 15, 2011, 01:25:44 AM

Code Select


;I translate this from syslinux
; It has a table function defined like this


PMVect struc
	nSize dword 0
	_lmalloc	dd 0    
	_lfree	dd 0    
	_open_file	dd 0    
	_read_file	dd 0    
	_close_file	dd 0    
	_opendir	dd 0    
	_readdir	dd 0    
	_closedir	dd 0    
	_idle	dd 0    
	_reset_idle	dd 0    
	_chdir	dd 0    
	_getcwd	dd 0    
	_jiffies	dd 0    
	_ms_timer	dd 0
PMVect ends

PM_VEC_TABLE dd OFFSET nSize dword, OFFSET _lmalloc,OFFSET_lfree, OFFSET_open_file	dd 0   ... etc. OFFSET _ms_time

GetPMVector proc

	mov eax,offset _ms_time
	
	ret
GetPMVector endp

OpenFile proc lpPointer:dword,lpName:dword

mov ecx,lpPointer
push lpname
call [ecx].PMVect._open_file
add esp,4

 ret
OpenFile endp


;Here is how you used it

Invoke GetVectoreTable
invoke OpenFile,eax,CADD("MyFile.txt")

Title: Re: A function that accepts a function pointer
Post by: hutch-- on October 16, 2011, 01:52:45 AM

its pretty easy, get the ADDRESS of the function and pass it to another function as a single DWORD value.

Now with the receiving function, it needs to be able to call the passed function, the low level way to do this is to use the PUSH / CALL technique common in MASM programming.

Pseudo code.

Code Select


called_function proc fptr:DWORD, any other args etc ...

    LOCAL retval  :DWORD

    push arg3    ; args required by the passed function
    puch arg2
    push arg1
    call fptr

    mov retval, eax  ; get its return value

  ; any other code

    ret

called_function endp

The MASM Forum Archive 2004 to 2012

General Forums => The Campus => Topic started by: bf2 on October 13, 2011, 12:57:22 PM