Assembly Language Programming

May 21, 2015

FASM – A Simple Win32 Text Editor

Filed under: Assembly Language, C++ — Tags: , , , — programmer209 @ 10:54 am

This post shows how to implement a simple text editor in x86 assembly language using FASM – the Flat Assembler.

The main purpose here is to demonstrate how to use the Win32 file functions to open and save files.

Related Posts

FASM – A Simple Win32 HEX Editor

FASM – Win32 Hello World

The Edit Window

The starting point is to create a frame window as in my previous Hello World project. Then a windows Edit control is created as a child window within the client area of the frame window. This is done when the WM_CREATE message is handled in the Window Procedure (WndProc), after the frame window has been created. The window class for the child is set to the pre-defined class “EDIT”, which makes it into a windows Edit control, with all of the functionality needed for a basic text editor.

The Win32 File Functions

To open a file for reading or writing use the Win32 CreateFile function. This returns a file handle that must be used in any read or write operations on that file. Once the file is no longer needed, the CloseHandle function must be used to close the file handle.

To read text from an open file, first the GetFileSize function is called to determine the size of the file. Then a buffer is dynamically allocated and the ReadFile function is called to load the contents of the file into this buffer. The SetWindowText function is used to set the text of the Edit control to the contents of the buffer. The buffer must be null terminated to be accepted by this function, therefore the size of the buffer needs to be (file_size + 1).

To write text to an open file, first the GetWindowTextLength function is called to determine the length of the text in the Edit control. A buffer of size (length + 1) is dynamically allocated, and then filled with null terminated text from the Edit control by calling the GetWindowText function. The WriteFile function is then called to write the text to file, minus the null terminator.

Win32 Heap Allocation

Memory for the buffer that will hold the text bytes is dynamically allocated from the process heap. Before memory can be allocated, a handle to the default process heap needs to be obtained, which is done by calling the GetProcessHeap function. Then the HeapAlloc function is called to allocate memory for the buffer. When the buffer is no longer needed, call HeapFree to free the memory.

Accelerator Table

In the resource section of the code, an accelerator table is defined to handle the key combinations Ctrl+N, Ctrl+O, Ctrl+S and Ctrl+A. Whenever any of these key conbinations are pressed, the TranslateAccelerator function in the main message loop will translate them into WM_COMMAND messages and send them to the window procedure (WndProc).

The accelerator table maps Ctrl+N, Ctrl+O, and Ctrl+S to the menu command IDs: IDM_NEW, IDM_OPEN, and IDM_SAVE.

Select All

The windows Edit control already handles key combinations such as Ctrl+C (copy), Ctrl+V (paste), Ctrl+X (cut), and Ctrl+Z (undo). But it doesn’t handle Ctrl+A (select all), so I have simply added an entry to the accelerator table to handle this key combination.

The FASM Code

To grab this code, select with the mouse and then copy and paste directly into the FASM IDE.

Note: use CINVOKE to call memset, not INVOKE.

; -------------------------------------------------------------------------------------

 format PE GUI 4.0

 entry win_main

 include 'win32a.inc'

; -------------------------------------------------------------------------------------

 IDR_MY_MENU = 1

 IDM_FILE = 100
 IDM_NEW = 101
 IDM_OPEN = 102
 IDM_SAVE = 103
 IDM_SAVE_AS = 104
 IDM_EXIT = 105

 IDR_ACCEL = 106
 ID_SELECT_ALL = 107

; -------------------------------------------------------------------------------------

 section '.code' code readable executable

  win_main:

	; initialise the members of the wcex structure

	; --------------------------------------------

	; WNDCLASSEX

	; UINT cbSize
	; UINT style
	; WNDPROC lpfnWndProc
	; int cbClsExtra
	; int cbWndExtra
	; HINSTANCE hInstance
	; HICON hIcon
	; HCURSOR hCursor
	; HBRUSH hbrBackground
	; LPCTSTR lpszMenuName
	; LPCTSTR lpszClassName
	; HICON hIconSm

	; --------------------------------------------

	; the instance handle

	invoke GetModuleHandle,0

	mov [wcex.hInstance],eax

	; cbSize

	mov eax,sizeof.WNDCLASSEX

	mov [wcex.cbSize],eax

	; the windows proc

	mov [wcex.lpfnWndProc],WndProc

	; the windows style

	mov [wcex.style],CS_HREDRAW+CS_VREDRAW

	; load the icons

	invoke LoadIcon,[wcex.hInstance],IDI_APPLICATION

	mov [wcex.hIcon],eax

	mov [wcex.hIconSm],eax

	; load the cursor

	invoke LoadCursor,NULL,IDC_ARROW

	mov [wcex.hCursor],eax

	; the brush for the background

	mov [wcex.hbrBackground],COLOR_BTNFACE+1

	; the windows class name

	mov dword [wcex.lpszClassName],szClass

	; set to NULL

	mov [wcex.cbClsExtra],0

	mov [wcex.cbWndExtra],0

	mov dword [wcex.lpszMenuName],NULL

	; register wcex

	; RegisterClassEx(&wcex)

	invoke RegisterClassEx,wcex

	test eax,eax

	jz reg_error

	; load the menu

	invoke LoadMenu,[wcex.hInstance],IDR_MY_MENU

	mov [h_menu],eax

	; create the main window

	invoke CreateWindowEx,0,szClass,szTitle,WS_OVERLAPPEDWINDOW,\
			      CW_USEDEFAULT,CW_USEDEFAULT,\
			      700,500,NULL,[h_menu],[wcex.hInstance],NULL

	; save the windows handle:

	mov [h_wnd],eax

	test eax,eax

	jz cr_error

	; load the accelerator table

	invoke LoadAccelerators,[wcex.hInstance],IDR_ACCEL

	test eax,eax

	jz acc_error

	mov [h_accel],eax

	; show and update the window

	; ShowWindow(hWnd,SW_SHOWNORMAL)

	invoke ShowWindow,[h_wnd],SW_SHOWNORMAL

	; UpdateWindow(hWnd)

	invoke UpdateWindow,[h_wnd]

  msg_loop:

	; the main message loop

	; GetMessage(&msg,NULL,0,0)

	invoke GetMessage,msg,NULL,0,0

	cmp eax,1

	jb exit

	jne msg_loop

	; TranslateAccelerator(hwnd,h_accel,&msg)

	invoke TranslateAccelerator,[h_wnd],[h_accel],msg

	test eax,eax

	; no need to call TranslateMessage and DispatchMessage,

	; if an accelerator is successfully translated

	jnz msg_loop

	; TranslateMessage(&msg)

	invoke TranslateMessage,msg

	; DispatchMessage(&msg)

	invoke DispatchMessage,msg

	jmp msg_loop

  reg_error:

	invoke MessageBox,NULL,szRegError,szTitle,MB_ICONERROR+MB_OK

	jmp exit

  cr_error:

	invoke MessageBox,NULL,szCreateError,szTitle,MB_ICONERROR+MB_OK

	jmp exit

  acc_error:

	invoke MessageBox,NULL,szAccelError,szTitle,MB_ICONERROR+MB_OK

  exit:

	; return msg.wParam

	invoke ExitProcess,[msg.wParam]

; -------------------------------------------------------------------------------------

proc WndProc uses ebx esi edi,hwnd,wmsg,wparam,lparam

  ; WndProc(hwnd,wmsg,wparam,lparam)

  ; callback function to process messages for the main window

	cmp [wmsg],WM_CREATE

	je .ON_CREATE

	cmp [wmsg],WM_SIZE

	je .SIZE

	cmp [wmsg],WM_SETFOCUS

	je .SET_FOCUS

	cmp [wmsg],WM_COMMAND

	je .COMMAND

	cmp [wmsg],WM_DESTROY

	je .DESTROY

  .DEFAULT:

	; DefWindowProc(hWnd,wmsg,wParam,lParam)

	invoke DefWindowProc,[hwnd],[wmsg],[wparam],[lparam]

	jmp .DONE

  .ON_CREATE:

	; create the child EDIT control

	invoke CreateWindowEx,WS_EX_CLIENTEDGE,szEdit,0,\
	WS_VISIBLE+WS_CHILD+WS_VSCROLL+ES_AUTOVSCROLL+ES_MULTILINE,\
	0,0,0,0,[hwnd],0,[wcex.hInstance],NULL

	test eax,eax

	jz .EDIT_FAILED

	mov [h_wnd_edit],eax

	; create a font for the edit control

	invoke CreateFont,18,0,0,0,FW_NORMAL,FALSE,FALSE,FALSE,ANSI_CHARSET,\
	OUT_DEVICE_PRECIS,CLIP_DEFAULT_PRECIS,PROOF_QUALITY,FIXED_PITCH+FF_DONTCARE,szFontFace

	test eax,eax

	jz .FONT_FAILED

	mov [h_font],eax

	invoke SendMessage,[h_wnd_edit],WM_SETFONT,[h_font],FALSE

	xor eax,eax

	jmp .DONE

  .EDIT_FAILED:

	invoke MessageBox,NULL,szCreateError,szTitle,MB_ICONERROR+MB_OK

	jmp .DONE

  .FONT_FAILED:

	invoke MessageBox,NULL,szFontError,szTitle,MB_ICONERROR+MB_OK

	jmp .DONE

  .SIZE:

	; resize the child window

	; new width = LOWORD(lParam)

	; new height = HIWORD(lParam)

	mov eax,[lparam]

	and eax,0xffff

	mov edx,[lparam]

	shr edx,16

	invoke MoveWindow,[h_wnd_edit],0,0,eax,edx,TRUE

	xor eax,eax

	jmp .DONE

  .SET_FOCUS:

	; set the focus to the child EDIT control

	invoke SetFocus,[h_wnd_edit]

	xor eax,eax

	jmp .DONE

  .COMMAND:

	mov eax,[wparam]

	and eax,0xffff

	cmp eax,IDM_NEW

	je .NEW

	cmp eax,IDM_OPEN

	je .OPEN

	cmp eax,IDM_SAVE

	je .SAVE

	cmp eax,IDM_SAVE_AS

	je .SAVE_AS

	cmp eax,IDM_EXIT

	je .DESTROY

	cmp eax,ID_SELECT_ALL

	je .SELECT_ALL

	jmp .DEFAULT

  .NEW:

	; File|New or CTRL+N

	; clear the Edit window

	invoke SendMessage,[h_wnd_edit],WM_SETTEXT,0,0

	invoke SetWindowText,[hwnd],szTitle

	; reset the file name

	lea esi,[szFileName]

	mov [esi],byte 0

	xor eax,eax

	jmp .DONE

  .OPEN:

	; File|Open or CTRL+O

	stdcall File_Open,[hwnd]

	test eax,eax

	jz .DONE

	; load the file contents into the Edit window

	stdcall Text_From_File

	invoke SetWindowText,[hwnd],szFileName

	xor eax,eax

	jmp .DONE

  .SAVE:

	; File|Save or CTRL+S

	; if there isn't a valid file name,

	; call the File Save As dialog

	cmp [szFileName],byte 0

	jnz .TXT_TO_FILE

	stdcall File_Save_As,[hwnd]

	test eax,eax

	jz .DONE

	invoke SetWindowText,[hwnd],szFileName

  .TXT_TO_FILE:

	; save the Edit window text to the file

	stdcall Text_To_File

	xor eax,eax

	jmp .DONE

  .SAVE_AS:

	; File|Save As

	stdcall File_Save_As,[hwnd]

	test eax,eax

	jz .DONE

	invoke SetWindowText,[hwnd],szFileName

	; save the Edit window text to the file

	stdcall Text_To_File

	xor eax,eax

	jmp .DONE

  .SELECT_ALL:

	; CTRL+A (via Accerlerator Table)

	invoke SendMessage,[h_wnd_edit],EM_SETSEL,0,-1

	xor eax,eax

	jmp .DONE

  .DESTROY:

	; destroy the font

	invoke DeleteObject,[h_font]

	; PostQuitMessage(0)

	invoke PostQuitMessage,0

	xor eax,eax

  .DONE:

	ret

endp

; -------------------------------------------------------------------------------------

proc File_Open,hwnd

  ; display the GetOpenFileName dialog to get the file name

  ; then load the contents of the file into the Edit window

	; zero ofn - the OPENFILENAME struct

	mov eax,sizeof.OPENFILENAME

	cinvoke memset,ofn,0,eax

	; initialise the members of ofn

	mov eax,sizeof.OPENFILENAME

	mov [ofn.lStructSize],eax

	mov eax,[hwnd]

	mov [ofn.hwndOwner],eax

	; the filter

	mov eax,szFilter

	mov [ofn.lpstrFilter],eax

	lea eax,[szFileName]

	mov [ofn.lpstrFile],eax

	mov eax,MAX_PATH

	mov [ofn.nMaxFile],eax

	mov eax,OFN_EXPLORER
	or eax,OFN_FILEMUSTEXIST
	or eax,OFN_HIDEREADONLY

	mov [ofn.Flags],eax

	mov eax,szDefFileExtension

	mov [ofn.lpstrDefExt],eax

	; display the dialog to get szFileName

	invoke GetOpenFileName,ofn

	ret

endp

; -------------------------------------------------------------------------------------

proc File_Save_As,hwnd

  ; display the GetSaveFileName dialog to get the file name

  ; then save the contents of the Edit window to the file

	; zero ofn - the OPENFILENAME struct

	mov eax,sizeof.OPENFILENAME

	cinvoke memset,ofn,0,eax

	; initialise the members of ofn

	mov eax,sizeof.OPENFILENAME

	mov [ofn.lStructSize],eax

	mov eax,[hwnd]

	mov [ofn.hwndOwner],eax

	; the filter

	mov eax,szFilter

	mov [ofn.lpstrFilter],eax

	lea eax,[szFileName]

	mov [ofn.lpstrFile],eax

	mov eax,MAX_PATH

	mov [ofn.nMaxFile],eax

	mov eax,OFN_EXPLORER
	or eax,OFN_PATHMUSTEXIST
	or eax,OFN_HIDEREADONLY
	or eax,OFN_OVERWRITEPROMPT

	mov [ofn.Flags],eax

	mov eax,szDefFileExtension

	mov [ofn.lpstrDefExt],eax

	; display the dialog to get szFileName

	invoke GetSaveFileName,ofn

	ret

endp

; -------------------------------------------------------------------------------------

proc Text_From_File uses ebx esi edi

  ; load the contents of the file into the Edit window

	; get a handle to the default heap for this process

	invoke GetProcessHeap

	test eax,eax

	jz .HEAP_FAILED

	mov [h_heap],eax

	; open the file

	invoke CreateFile,szFileName,GENERIC_READ,FILE_SHARE_READ,NULL,\
	OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,NULL

	test eax,eax

	jz .CRF_FAILED

	; get the file handle

	mov [h_file],eax

	; get the file size

	invoke GetFileSize,[h_file],NULL

	cmp eax,0xffffffff

	je .INVALID_SIZE

	mov [FileSize],eax

	; allocate (FileSize + 1) bytes, with the extra byte for the null terminator

	inc eax

	; allocate nBytes from the heap for the buffer

	invoke HeapAlloc,[h_heap],NULL,eax

	test eax,eax

	jz .ALLOC_FAILED

	; point pFileBuffer to the buffer

	mov [pFileBuffer],eax

	; read the contents of the file into the buffer

	invoke ReadFile,[h_file],[pFileBuffer],[FileSize],nBytes,NULL

	test eax,eax

	jz .READ_FAILED

	; null terminate the file buffer

	mov esi,[pFileBuffer]

	add esi,[FileSize]

	mov [esi],byte 0

	; set the text of the Edit window

	invoke SetWindowText,[h_wnd_edit],[pFileBuffer]

  .FREE:

	invoke HeapFree,[h_heap],NULL,[pFileBuffer]

  .HCLOSE:

	invoke CloseHandle,[h_file]

	jmp .DONE

  .READ_FAILED:

	invoke MessageBox,NULL,szReadError,szTitle,MB_ICONERROR+MB_OK

	jmp .FREE

  .INVALID_SIZE:

	invoke MessageBox,NULL,szSizeError,szTitle,MB_ICONERROR+MB_OK

	jmp .HCLOSE

  .ALLOC_FAILED:

	invoke MessageBox,NULL,szAllocError,szTitle,MB_ICONERROR+MB_OK

	jmp .HCLOSE

  .CRF_FAILED:

	invoke MessageBox,NULL,szFileError,szTitle,MB_ICONERROR+MB_OK

	jmp .DONE

  .HEAP_FAILED:

	invoke MessageBox,NULL,szHeapError,szTitle,MB_ICONERROR+MB_OK

  .DONE:

	ret

endp

; -------------------------------------------------------------------------------------

proc Text_To_File uses ebx esi edi

  ; save the contents of the Edit window to the file

	; get a handle to the default heap for this process

	invoke GetProcessHeap

	test eax,eax

	jz .HEAP_FAILED

	mov [h_heap],eax

	; get the number of bytes in the Edit window

	invoke GetWindowTextLength,[h_wnd_edit]

	; +1 for the null terminator

	inc eax

	mov [nBytes],eax

	; allocate nBytes from the heap for the buffer

	invoke HeapAlloc,[h_heap],NULL,eax

	test eax,eax

	jz .ALLOC_FAILED

	; point pFileBuffer to the buffer

	mov [pFileBuffer],eax

	; open the file, create it if it doesn't exist

	invoke CreateFile,szFileName,GENERIC_WRITE,0,NULL,\
	CREATE_ALWAYS,FILE_ATTRIBUTE_NORMAL,NULL

	test eax,eax

	jz .CRF_FAILED

	; get the file handle

	mov [h_file],eax

	; read the contents of the Edit window into the buffer

	invoke GetWindowText,[h_wnd_edit],[pFileBuffer],[nBytes]

	; EAX now contains the size of pFileBuffer, not including the null terminator

	; write the buffer to the file

	invoke WriteFile,[h_file],[pFileBuffer],eax,nBytes,NULL

  .HCLOSE:

	invoke CloseHandle,[h_file]

  .FREE:

	invoke HeapFree,[h_heap],NULL,[pFileBuffer]

	jmp .DONE

  .ALLOC_FAILED:

	invoke MessageBox,NULL,szAllocError,szTitle,MB_ICONERROR+MB_OK

	jmp .DONE

  .CRF_FAILED:

	invoke MessageBox,NULL,szFileError,szTitle,MB_ICONERROR+MB_OK

	jmp .FREE

  .HEAP_FAILED:

	invoke MessageBox,NULL,szHeapError,szTitle,MB_ICONERROR+MB_OK

  .DONE:

	ret

endp

; -------------------------------------------------------------------------------------

section '.idata' import data readable writeable

  library kernel,'KERNEL32.DLL',\
	  user,'USER32.DLL',\
	  comdlg32,'COMDLG32.DLL',\
	  gdi,'GDI32.DLL',\
	  msvcrt,'MSVCRT.DLL'

  import kernel,\
	 GetModuleHandle,'GetModuleHandleA',\
	 ExitProcess,'ExitProcess',\
	 GetFileSize,'GetFileSize',\
	 CloseHandle,'CloseHandle',\
	 CreateFile,'CreateFileA',\
	 ReadFile,'ReadFile',\
	 WriteFile,'WriteFile',\
	 GetProcessHeap,'GetProcessHeap',\
	 HeapAlloc,'HeapAlloc',\
	 HeapFree,'HeapFree'

  import user,\
	 RegisterClassEx,'RegisterClassExA',\
	 CreateWindowEx,'CreateWindowExA',\
	 ShowWindow,'ShowWindow',\
	 UpdateWindow,'UpdateWindow',\
	 MoveWindow,'MoveWindow',\
	 GetMessage,'GetMessageA',\
	 SendMessage,'SendMessageA',\
	 TranslateMessage,'TranslateMessage',\
	 DispatchMessage,'DispatchMessageA',\
	 MessageBox,'MessageBoxA',\
	 DefWindowProc,'DefWindowProcA',\
	 PostQuitMessage,'PostQuitMessage',\
	 SetFocus,'SetFocus',\
	 LoadIcon,'LoadIconA',\
	 LoadMenu,'LoadMenuA',\
	 LoadCursor,'LoadCursorA',\
	 SetWindowText,'SetWindowTextA',\
	 GetWindowText,'GetWindowTextA',\
	 GetWindowTextLength,'GetWindowTextLengthA',\
	 LoadAccelerators,'LoadAcceleratorsA',\
	 TranslateAccelerator,'TranslateAcceleratorA'

  import comdlg32,\
	 GetOpenFileName,'GetOpenFileNameA',\
	 GetSaveFileName,'GetSaveFileNameA'

  import gdi,\
	 CreateFont,'CreateFontA',\
	 DeleteObject,'DeleteObject'

  import msvcrt,\
	 memset,'memset'

; -------------------------------------------------------------------------------------

section '.data' readable writeable

  szClass TCHAR "Win32app",0

  szTitle TCHAR "Text Editor",0 

  szEdit TCHAR "EDIT",0

  szRegError TCHAR "Call to RegisterClassEx failed!",0

  szCreateError TCHAR "Call to CreateWindowEx failed!",0

  szFontError TCHAR "Call to CreateFont failed!",0

  szFileError TCHAR "Call to CreateFile failed!",0

  szReadError TCHAR "Call to ReadFile failed!",0

  szAllocError TCHAR "Call to HeapAlloc failed!",0

  szHeapError TCHAR "Call to GetProcessHeap failed!",0

  szSizeError TCHAR "Call to GetFileSize failed!",0

  szAccelError TCHAR "Call to LoadAccelerators failed!",0

  szFontFace TCHAR "Lucida Console",0

  szDefFileExtension TCHAR "txt",0

  ; Note that the filter string is double null terminated:

  szFilter TCHAR "Text Files (*.txt)",0,"*.txt",0,"All Files (*.*)",0,"*.*",0,0

  szFileName rb MAX_PATH

  ofn OPENFILENAME

  wcex WNDCLASSEX

  msg MSG

  h_wnd dd 0

  h_wnd_edit dd 0

  h_font dd 0

  h_menu dd 0

  h_file dd 0

  h_heap dd 0

  h_accel dd 0

  FileSize dd 0

  nBytes dd 0

  pFileBuffer dd 0

; -------------------------------------------------------------------------------------

section '.rc' resource data readable

  directory RT_MENU,menus,\
	    RT_ACCELERATOR,accelerators

  resource menus,IDR_MY_MENU,LANG_ENGLISH+SUBLANG_DEFAULT,my_menu

  resource accelerators,IDR_ACCEL,LANG_ENGLISH+SUBLANG_DEFAULT,accel_keys

  menu my_menu

  menuitem 'File',IDM_FILE,MFR_POPUP+MFR_END
  menuitem 'New',IDM_NEW
  menuitem 'Open',IDM_OPEN
  menuitem 'Save',IDM_SAVE
  menuitem 'Save As',IDM_SAVE_AS
  menuseparator
  menuitem 'Exit',IDM_EXIT,MFR_END

  accelerator accel_keys,\
	      FVIRTKEY+FNOINVERT+FCONTROL,'N',IDM_NEW,\
	      FVIRTKEY+FNOINVERT+FCONTROL,'O',IDM_OPEN,\
	      FVIRTKEY+FNOINVERT+FCONTROL,'S',IDM_SAVE,\
	      FVIRTKEY+FNOINVERT+FCONTROL,'A',ID_SELECT_ALL

; -------------------------------------------------------------------------------------

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