In a previous post we built a boilerplate program that we can start to work with. For today’s post, we’re going to go through the development of a resource file that you can incorporate into your own projects.
What are resource files?
You can use resource files to organise your external resources (images, audio, text, etc.) into a compilable (and ultimately linkable) resource. The items that you add to your resource file are then statically added to your resulting executable, ready for you to reference.
You should place every element of the user interface that needs to be localized in a Windows resource file, including pictures, strings, messages, menus, dialog boxes, and version information. The table below lists the individual resource elements defined by Windows.
Resource Type
Element
File Format
Comment/ Description
RT_CURSOR
Cursor
.CUR
#include in .RC file
RT_BITMAP
Bitmap or toolbar
.BMP
#include in .RC file
RT_ICON
Icon
.ICO
#include in .RC file
RT_MENU
Menu or pop up menu
.RC
#include in .RC file
RT_DIALOG
Dialog
.DLG or .RC
#include .DLG file in .RC file
RT_STRING
String
.RC
RT_FONTDIR
Font
.FNT
RT_FONT
Font
.FNT
RT_ACCELERATORS
Accelerator
.RC
RT_RCDATA
User-defined resource
.RC
Can use for constants or application specific structures
RT_MESSAGETABLE
Messages
.MC
#include compiled message table in .RC file
RT_GROUP_CURSOR
Cursor
N/A
Generated internally by resource compiler to provide Windows with information about cursor’s resolution and type
RT_GROUP_ICON
Icon
N/A
Generated internally by resource compiler to provide Windows with information about icon’s resolution and type
RT_VERSION
Version information
.RC
RT_DLGINCLUDE
Header file that contains menu and dialog box #define statements
.RC
Used by resource editing tools; Visual C++ uses its own mechanism tools;
What does a resource file look like?
The .RC file itself is just text. There are IDs that are defined throughout that you can create symbolic constants for in your code, just so you’re not doing so much “magic number” work. Here’s a simple menu:
600 MENUEX MOVEABLE IMPURE LOADONCALL DISCARDABLE
BEGIN
POPUP "&File", , , 0
BEGIN
MENUITEM "&Exit", 1000
END
POPUP "&Help", , , 0
BEGIN
MENUITEM "&About", 1900
END
END
600 in this example is the ID of the menu. Referencing this menu in your code is as simple as passing 600 to the menu name parameter of a LoadMenu call:
In a previous post I wrote about the basics of getting a program written and compiled using masm32 for the windows platform. In today’s post, I’m going to walkthrough the basic anatomy of a windows program that play the key roles in your application.
This information is language agnostic. It’s standard windows programming knowledge that I’ll present in the form of assembly programming with masm32. By the end of this blog post, you’ll have a good starting point (in boilerplate code) for any program that you want to write with masm32.
The basic pieces
In any windows program (using the Win32 API) there are some basic pieces that you’ll see most of the time.
Main entry point (WinMain)
Window creation
Window handler procedure (WNDPROC)
Message pump
These basic building blocks that you’ll see in just about all windows applications.
WinMain
This is your application’s main entry point. It’s analogous to the main function that you use when writing applicatioons in C/C++. From Microsoft’s site:
The user-provided entry point for a graphical Windows-based application.
Being at the assembly layer, we’re exposed a little earlier in the process than what WinMain affords us, so we have extra work to do in terms of getting our application running. We as the implementers of the program need to invoke WinMain directly as this is not done for us.
GetModuleHandle allows us to fill the hInstance parameter and GetCommandLine gives us lpszCmdLine. hPrevInstance, according to the documentation is always NULL and nShowCmd is an SW_ series value that controls how our main application window is shown.
Window creation
The creation of a window is broken down into a few smaller steps:
Register a window class
Create the window
Show the window
Registering a window class is just filling out the WNDCLASSEX structure and calling RegisterClassEx. Registering a windows class establishes base or common attributes about a window that you can re-use in subsequent calls to CreateWindow.
The macro szText is setup to allow you to ad-hoc define string variables where ever you need to. The rest of this is mainly filling out the structure and finally registering it. Setting lpfnWndProc has special significance to us here as we’ll go on to describe WNDPROC and its role in the application.
WindowProc callback function
When an application receives messages from the operating system, it handles this information through the window procedure. The window procedure interface is defined as:
You’ll use Nasm to reduce your assembly source code into COFF object files. Gorc will take your resource scripts and produce linkable object files from these. Finally, ALink will bind all of your object files into a windows executable.
Finally, you’re going to need a copy of the include file for the Win32 API. The API itself is huge; the number of constants and structures is mind boggling. The link above handles all of these for you.
Test program
Probably the easiest thing to accomplish, is showing a message box. You need to show the message box and then return control back to Windows. You do this with calls to MessageBoxA and ExitProcess. The “A” in MessageBoxA as we’re not dealing with the wide-char version of these functions.
Here’s the code.
%include "win32n.inc"
extern MessageBoxA
import MessageBoxA user32.dll
extern ExitProcess
import ExitProcess kernel32.dll
segment .data USE32
title db "A message for you", 0
message db "This is your first message", 0
segment .bss USE32
segment .code USE32
..start:
; show the message box
push MB_OK
push title
push message
push 0
call [MessageBoxA]
; return control back to windows
push 0
call [ExitProcess]
Functions are imported from the api using import, and are called in a very assembler-traditional fashion here. Taking a look at the definition for the MessageBox function, we can see the order of parameters:
Arguments are pushed to the stack in reverse order.
Assembling and linking
Now that you’ve got your source file, hello.asm you can produce an object file with the following:
C:\src> nasm -i c:\nasm\include -f obj hello.asm
You can now link the object file into an executable with the following:
C:\src> alink -c -oPE -subsys gui hello
Ready to go.
Making things a little more high-level
You can make your assembly code a little more high-level by using the nagoa+.inc include file. This include file provides your programs with some really handy constructs (as well as the win32 api bindings), so function invocations now look like this:
In this post, I’ll walk through the steps required to bootstrap your development experience against the Win32 API using the Microsoft’s Macro Assember.
Prerequisites
Downloading the package from the masm32.com site will be everything that you need to produce applications using assembly language. It not only includes the assember ml, but also includes all of the library, include files and linker for you.
Test program
Here’s the code to present a message box.
; #######################
.386
.model flat, stdcall
option casemap :none ; case sensitive
; #######################
include windows.inc
include user32.inc
include kernel32.inc
includelib user32.lib
includelib kernel32.lib
; #######################
.data
szTitle db "Your message", 0
szMsg db "First message box", 0
.code
start:
invoke MessageBox, 0, offset szMsg, offset szTitle, MB_OK
invoke ExitProcess, 0
end start
invoke goes a long way to cleaning up how any assembly program that is sub-routine heavy looks. The include files already do the externing of library symbols so that your code doesn’t need to explicitly declare that you’re using a particular function.
Assembling and linking
Now that you’ve got your source file, hello.asm you can produce an object file and executable with the following:
You can see that not only assembler switches are passed, but also linker switches which means you’re assembling and linking all in one step.
Conclusion
The bundle for masm32 that this article refers to is great in the amount of code that it offers you, but the provided assembler is well-dated. Microsoft have been keeping masm updated from their website with 64 bit versions available with their development tools.
In this post, I’ll walk through the steps required to bootstrap your development experience against the Win32 API using the Flat Assembler.
Prerequisites
Everything is provided for you when you download the fasmw package, including libraries, include files. fasmw even includes a linker pre-geared for windows as your target.
Test program
Here’s the code to present a message box.
include 'win32ax.inc'
.code
start:
invoke MessageBox, HWND_DESKTOP, 'This is a test', 'Hey, Hey!', MB_OK
invoke ExitProcess, 0
.end start
Everything is provided to you through win32ax.inc. This can be swapped out easily enough with a 64 bit counterpart if you’re targeting different architectures.
Assembling and linking
Now that you’ve got your source file, hello.asm you can produce an object file with the following:
C:\src> fasm hello.asm
That’s all there is to it. You’ll now have an exe available to you to run. The only gotcha is giving fasm a hint as to where your include files are, and you do this through the INCLUDE environment variable: