Tutorial 12: Memory Management and File I/O
Download the example here.
File I/O under Win32 bears remarkable semblance to that under DOS. The steps
needed are the same. You only have to change interrupts to API calls and it's
done. The required steps are the followings:
.386
.model flat,stdcall
option casemap:none
WinMain proto :DWORD,:DWORD,:DWORD,:DWORD
include \masm32\include\windows.inc
include \masm32\include\user32.inc
include \masm32\include\kernel32.inc
include \masm32\include\comdlg32.inc
includelib \masm32\lib\user32.lib
includelib \masm32\lib\kernel32.lib
includelib \masm32\lib\comdlg32.lib
.const
IDM_OPEN equ 1
IDM_SAVE equ 2
IDM_EXIT equ 3
MAXSIZE equ 260
MEMSIZE equ 65535
EditID equ 1 ; ID of the edit control
.data
ClassName db "Win32ASMEditClass",0
AppName db "Win32 ASM Edit",0
EditClass db "edit",0
MenuName db "FirstMenu",0
ofn OPENFILENAME <>
FilterString db "All Files",0,"*.*",0
db "Text Files",0,"*.txt",0,0
buffer db MAXSIZE dup(0)
.data?
hInstance HINSTANCE ?
CommandLine LPSTR ?
hwndEdit HWND ?
; Handle to the edit control
hFile HANDLE ?
; File handle
hMemory HANDLE ?
;handle to the allocated memory block
pMemory DWORD ?
;pointer to the allocated memory block
SizeReadWrite DWORD ?
; number of bytes actually read or write
.code
start:
invoke GetModuleHandle, NULL
mov hInstance,eax
invoke GetCommandLine
mov CommandLine,eax
invoke WinMain, hInstance,NULL,CommandLine, SW_SHOWDEFAULT
invoke ExitProcess,eax
WinMain proc hInst:HINSTANCE,hPrevInst:HINSTANCE,CmdLine:LPSTR,CmdShow:SDWORD
LOCAL wc:WNDCLASSEX
LOCAL msg:MSG
LOCAL hwnd:HWND
mov wc.cbSize,SIZEOF WNDCLASSEX
mov wc.style, CS_HREDRAW or CS_VREDRAW
mov wc.lpfnWndProc, OFFSET WndProc
mov wc.cbClsExtra,NULL
mov wc.cbWndExtra,NULL
push hInst
pop wc.hInstance
mov wc.hbrBackground,COLOR_WINDOW+1
mov wc.lpszMenuName,OFFSET MenuName
mov wc.lpszClassName,OFFSET ClassName
invoke LoadIcon,NULL,IDI_APPLICATION
mov wc.hIcon,eax
mov wc.hIconSm,eax
invoke LoadCursor,NULL,IDC_ARROW
mov wc.hCursor,eax
invoke RegisterClassEx, addr wc
invoke CreateWindowEx,WS_EX_CLIENTEDGE,ADDR ClassName,ADDR
AppName,\
WS_OVERLAPPEDWINDOW,CW_USEDEFAULT,\
CW_USEDEFAULT,300,200,NULL,NULL,\
hInst,NULL
mov hwnd,eax
invoke ShowWindow, hwnd,SW_SHOWNORMAL
invoke UpdateWindow, hwnd
.WHILE TRUE
invoke GetMessage, ADDR msg,NULL,0,0
.BREAK .IF (!eax)
invoke TranslateMessage, ADDR
msg
invoke DispatchMessage, ADDR msg
.ENDW
mov eax,msg.wParam
ret
WinMain endp
WndProc proc uses ebx hWnd:HWND, uMsg:UINT, wParam:WPARAM, lParam:LPARAM
.IF uMsg==WM_CREATE
invoke CreateWindowEx,NULL,ADDR
EditClass,NULL,\
WS_VISIBLE or WS_CHILD or ES_LEFT or ES_MULTILINE or\
ES_AUTOHSCROLL or ES_AUTOVSCROLL,0,\
0,0,0,hWnd,EditID,\
hInstance,NULL
mov hwndEdit,eax
invoke SetFocus,hwndEdit
;==============================================
; Initialize the members of OPENFILENAME
structure
;==============================================
mov ofn.lStructSize,SIZEOF ofn
push hWnd
pop ofn.hWndOwner
push hInstance
pop ofn.hInstance
mov ofn.lpstrFilter, OFFSET
FilterString
mov ofn.lpstrFile, OFFSET
buffer
mov ofn.nMaxFile,MAXSIZE
.ELSEIF uMsg==WM_SIZE
mov eax,lParam
mov edx,eax
shr edx,16
and eax,0ffffh
invoke MoveWindow,hwndEdit,0,0,eax,edx,TRUE
.ELSEIF uMsg==WM_DESTROY
invoke PostQuitMessage,NULL
.ELSEIF uMsg==WM_COMMAND
mov eax,wParam
.if lParam==0
.if ax==IDM_OPEN
mov ofn.Flags, OFN_FILEMUSTEXIST or \
OFN_PATHMUSTEXIST or OFN_LONGNAMES or\
OFN_EXPLORER or OFN_HIDEREADONLY
invoke GetOpenFileName, ADDR ofn
.if eax==TRUE
invoke CreateFile,ADDR buffer,\
GENERIC_READ or GENERIC_WRITE ,\
FILE_SHARE_READ or FILE_SHARE_WRITE,\
NULL,OPEN_EXISTING,FILE_ATTRIBUTE_ARCHIVE,\
NULL
mov hFile,eax
invoke GlobalAlloc,GMEM_MOVEABLE or GMEM_ZEROINIT,MEMSIZE
mov hMemory,eax
invoke GlobalLock,hMemory
mov pMemory,eax
invoke ReadFile,hFile,pMemory,MEMSIZE-1,ADDR SizeReadWrite,NULL
invoke SendMessage,hwndEdit,WM_SETTEXT,NULL,pMemory
invoke CloseHandle,hFile
invoke GlobalUnlock,pMemory
invoke GlobalFree,hMemory
.endif
invoke SetFocus,hwndEdit
.elseif
ax==IDM_SAVE
mov ofn.Flags,OFN_LONGNAMES or\
OFN_EXPLORER or OFN_HIDEREADONLY
invoke GetSaveFileName, ADDR ofn
.if eax==TRUE
invoke CreateFile,ADDR buffer,\
GENERIC_READ or GENERIC_WRITE ,\
FILE_SHARE_READ or FILE_SHARE_WRITE,\
NULL,CREATE_NEW,FILE_ATTRIBUTE_ARCHIVE,\
NULL
mov hFile,eax
invoke GlobalAlloc,GMEM_MOVEABLE or GMEM_ZEROINIT,MEMSIZE
mov hMemory,eax
invoke GlobalLock,hMemory
mov pMemory,eax
invoke SendMessage,hwndEdit,WM_GETTEXT,MEMSIZE-1,pMemory
invoke WriteFile,hFile,pMemory,eax,ADDR SizeReadWrite,NULL
invoke CloseHandle,hFile
invoke GlobalUnlock,pMemory
invoke GlobalFree,hMemory
.endif
invoke SetFocus,hwndEdit
.else
invoke DestroyWindow, hWnd
.endif
.endif
.ELSE
invoke
DefWindowProc,hWnd,uMsg,wParam,lParam
ret
.ENDIF
xor eax,eax
ret
WndProc endp
end start
In WM_CREATE section, we create an edit control. Note that the parameters that
specify x, y, width,height of the control are all zeroes since we will resize
the control later to cover the whole client area of the parent window.
Note that in this case, we don't have to call ShowWindow to make the edit control
appear on the screen because we include WS_VISIBLE style. You can use this trick
in the parent window too.
;==============================================
; Initialize the members of OPENFILENAME
structure
;==============================================
mov ofn.lStructSize,SIZEOF ofn
push hWnd
pop ofn.hWndOwner
push hInstance
pop ofn.hInstance
mov ofn.lpstrFilter, OFFSET
FilterString
mov ofn.lpstrFile, OFFSET
buffer
mov ofn.nMaxFile,MAXSIZE
After creating the edit control, we take this time to initialize the members
of ofn. Because we want to reuse ofn in the save as dialog box too, we fill
in only the *common* members that're used by both GetOpenFileName and GetSaveFileName.
WM_CREATE section is a great place to do once-only initialization.
.ELSEIF uMsg==WM_SIZE
mov eax,lParam
mov edx,eax
shr edx,16
and eax,0ffffh
invoke MoveWindow,hwndEdit,0,0,eax,edx,TRUE
We receive WM_SIZE messages when the size of the client area of our main window changes. We also receive it when the window is first created. In order to be able to receive this message, the window class styles must include CS_VREDRAW and CS_HREDRAW styles. We use this opportunity to resize our edit control to the same size as the client area of the parent window. First we have to know the current width and height of the client area of the parent window. We get this info from lParam. The high word of lParam contains the height and the low word of lParam the width of the client area. We then use the information to resize the edit control by calling MoveWindow function which, in addition to changing the position of the window, can alter the size too.
.if ax==IDM_OPEN
mov ofn.Flags, OFN_FILEMUSTEXIST or \
OFN_PATHMUSTEXIST or OFN_LONGNAMES or\
OFN_EXPLORER or OFN_HIDEREADONLY
invoke GetOpenFileName, ADDR ofn
When the user selects File/Open menu item, we fill in the Flags member of ofn structure and call GetOpenFileName function to display the open file dialog box.
.if eax==TRUE
invoke CreateFile,ADDR buffer,\
GENERIC_READ or GENERIC_WRITE ,\
FILE_SHARE_READ or FILE_SHARE_WRITE,\
NULL,OPEN_EXISTING,FILE_ATTRIBUTE_ARCHIVE,\
NULL
mov hFile,eax
After the user selects a file to open, we call CreateFile to open the file. We specifies that the function should try to open the file for read and write. After the file is opened, the function returns the handle to the opened file which we store in a global variable for future use. This function has the following syntax:
CreateFile proto lpFileName:DWORD,\
dwDesiredAccess:DWORD,\
dwShareMode:DWORD,\
lpSecurityAttributes:DWORD,\
dwCreationDistribution:DWORD\,
dwFlagsAndAttributes:DWORD\,
hTemplateFile:DWORD
dwDesiredAccess specifies which operation you want to perform on the file.
When the file is opened, we allocate a block of memory for use by ReadFile
and WriteFile functions. We specify GMEM_MOVEABLE flag to let Windows
move the memory block around to consolidate memory. GMEM_ZEROINIT flag tells
GlobalAlloc to fill the newly allocated memory block with zeroes.
When GlobalAlloc returns successfully, eax contains the handle to the allocated
memory block. We pass this handle to GlobalLock function which returns a pointer
to the memory block.
invoke ReadFile,hFile,pMemory,MEMSIZE-1,ADDR SizeReadWrite,NULL
invoke SendMessage,hwndEdit,WM_SETTEXT,NULL,pMemory
When the memory block is ready for use, we call ReadFile function to read data
from the file. When a file is first opened or created, the file pointer is at
offset 0. So in this case, we start reading from the first byte in the file
onwards. The first parameter of ReadFile is the handle of the file to read,
the second is the pointer to the memory block to hold the data, next is the
number of bytes to read from the file, the fourth param is the address of the
variable of DWORD size that will be filled with the number of bytes actually
read from the file.
After we fill the memory block with the data, we put the data into the edit
control by sending WM_SETTEXT message to the edit control with lParam containing
the pointer to the memory block. After this call, the edit control shows the
data in its client area.
invoke CloseHandle,hFile
invoke GlobalUnlock,pMemory
invoke GlobalFree,hMemory
.endif
At this point, we have no need to keep the file open any longer since our purpose is to write the modified data from the edit control to another file, not the original file. So we close the file by calling CloseHandle with the file handle as its parameter. Next we unlock the memory block and free it. Actually you don't have to free the memory at this point, you can reuse the memory block during the save operation later. But for demonstration purpose , I choose to free it here.
invoke SetFocus,hwndEdit
When the open file dialog box is displayed on the screen, the input focus shifts
to it. So after the open file dialog is closed, we must move the input focus
back to the edit control.
This end the read operation on the file. At this point, the user can edit the
content of the edit control.And when he wants to save the data to another file,
he must select File/Save as menuitem which displays a save as dialog box. The
creation of the save as dialog box is not much different from the open file
dialog box. In fact, they differ in only the name of the functions, GetOpenFileName
and GetSaveFileName. You can reuse most members of the ofn structure too except
the Flags member.
mov ofn.Flags,OFN_LONGNAMES or\
OFN_EXPLORER or OFN_HIDEREADONLY
In our case, we want to create a new file, so OFN_FILEMUSTEXIST and OFN_PATHMUSTEXIST
must be left out else the dialog box will not let us create a file that doesn't
already exist.
The dwCreationDistribution parameter of the CreateFile function must be changed
to CREATE_NEW since we want to create a new file.
The remaining code is identical to those in the open file section except the
following:
invoke SendMessage,hwndEdit,WM_GETTEXT,MEMSIZE-1,pMemory
invoke WriteFile,hFile,pMemory,eax,ADDR SizeReadWrite,NULL
We send WM_GETTEXT message to the edit control to copy the data from it to the memory block we provide, the return value in eax is the length of the data inside the buffer. After the data is in the memory block, we write them to the new file.