Tutorial 12: Memory Management and File I/O
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:
Open or Create the file by calling CreateFile function. This function is very versatile: in addition to files, it can open communication ports, pipes, disk drives or console. On success, it returns a handle to file or device. You can then use this handle to perform operations on the file or device. Move the file pointer to the desired location by calling SetFilePointer. Perform read or write operation by calling ReadFile or WriteFile. These functions transfer data from a block of memory to or from the file. So you have to allocate a block of memory large enough to hold the data. Close the file by calling CloseHandle. This function accepts the file handle..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.
0 Open the file to query its attributes. You have to rights to read or write the data. GENERIC_READ Open the file for reading. GENERIC_WRITE Open the file for writing. dwShareMode specifies which operation you want to allow other processes to perform on the file that 's being opened. 0 Don't share the file with other processes. FILE_SHARE_READ allow other processes to read the data from the file being opened FILE_SHARE_WRITE allow other processes to write data to the file being opened. lpSecurityAttributes has no significance under Windows 95. dwCreationDistribution specifies the action CreateFile will perform when the file specified in lpFileName exists or when it doesn't exist. CREATE_NEW Creates a new file. The function fails if the specified file already exists. CREATE_ALWAYS Creates a new file. The function overwrites the file if it exists. OPEN_EXISTING Opens the file. The function fails if the file does not exist. OPEN_ALWAYS Opens the file, if it exists. If the file does not exist, the function creates the file as if dwCreationDistribution were CREATE_NEW. TRUNCATE_EXISTING Opens the file. Once opened, the file is truncated so that its size is zero bytes. The calling process must open the file with at least GENERIC_WRITE access. The function fails if the file does not exist. dwFlagsAndAttributes specifies the file attributes FILE_ATTRIBUTE_ARCHIVE The file is an archive file. Applications use this attribute to mark files for backup or removal. FILE_ATTRIBUTE_COMPRESSED The file or directory is compressed. For a file, this means that all of the data in the file is compressed. For a directory, this means that compression is the default for newly created files and subdirectories. FILE_ATTRIBUTE_NORMAL The file has no other attributes set. This attribute is valid only if used alone. FILE_ATTRIBUTE_HIDDEN The file is hidden. It is not to be included in an ordinary directory listing. FILE_ATTRIBUTE_READONLY The file is read only. Applications can read the file but cannot write to it or delete it. FILE_ATTRIBUTE_SYSTEM The file is part of or is used exclusively by the operating system. invoke GlobalAlloc,GMEM_MOVEABLE or GMEM_ZEROINIT,MEMSIZE mov hMemory,eax invoke GlobalLock,hMemory mov pMemory,eaxWhen 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.
