Win32 API - Windows Programming Tutorial

SkeletonC is a command-line program written in C language. Visual C++ AppWizard automatically generated all files for this project. If you look at the source code, you will notice that it is just plain C program that uses main() as the entry point and displays some texts to the command-line standard output. The program doesn't use any GUI element for interacting with the user. The entire program is reproduced below.

// SkeletonC.cpp : Defines the entry point for the console application.

#include "stdafx.h"

int main(int argc, char* argv[])

{

printf("Hello World!\n");

return 0;

}

Like any other C program, it has a mandatory entry point function, main(). The program starts execution from this function, and when this function returns, the entire program ends. SkeletonC interacts with the user by means of a standard I/O function, printf. It could use other functions like scanf to read user input from the command-line.

An interesting thing about SkeletonC is that it is not really the simplest kind of program that runs on Windows operating system. On the other hand, it is more complicated than the program that will be discussed next, SkeletonNW. We will come back to this topic after we look at SkeletonNW.

SkeletonNW

This program is a pure Windows application that just doesn't display a window or any other graphical user interface element such as buttons. Visual C++ AppWizard automatically generated all files for this project.

// SkeletonNW.cpp : Defines the entry point for the application.

#include "stdafx.h"

int APIENTRY WinMain(HINSTANCE hInstance,

HINSTANCE hPrevInstance,

LPSTR lpCmdLine,

int nCmdShow)

{

// TODO: Place code here.

return 0;

}

Entry point of Windows application: WinMain

WinMain is the entry point of the SkeletonNW program. It is equivalent of main() function in C program. When Windows operating system loads SkeletonNW, it starts executing this function (in fact, it's the only function in SkeletonNW), which doesn't do much in its body.

Sequential execution model

Comparing the program behavior of SkeletonNW with SkeletonC, you notice that they both execute sequentially in top-down manner. When the execution reaches the end of main() or WinMain(), that's the end of the programs. This sequential behavior is what many C programmers are used to. In fact, there is absolutely nothing wrong with writing a Windows application that simply runs code sequentially and exits. On the other hand, typical Windows applications that we know, like Word and Internet Explorer, are all event-driven. In the next chapter, we will see "Event-driven execution model" in detail.

Revisiting SkeletonC

SkeletonNW, discussed in the previous section, is a truly minimal Windows application – Windows operating system loads it into the memory and transfer control to WinMain(), which is the starting point of your program. SkeletonC, on the other hand, actually involves a helper code: it actually runs on top of a layer of code called "C Run-time (CRT) Startup code". CRT Startup code has WinMain() function, which Windows calls when loaded, and it sets up the environment where a plain C program like SkeletonC can run. CRT Startup code emulates a command-line execution environment. This is to say that CRT Startup graphically draws any text printed out in the command-line window.

Subsequent sample programs will not be based on SkeletonC because of the extra layer of CRT Startup code. To understand structures of Windows applications from ground up, we will start with SkeletonNW instead.

Regular Windows Application

Regular Windows application program is a typical application program that has some graphical user interface element (GUI element), especially an application window that sets a graphical boundary on the screen while running. Most Windows applications that we know fall into this category: Microsoft Word, Netscape, Internet Explorer, Notepad, etc. A vast majority of Windows applications are of this type.

Please note that the term "regular Windows application" is not an industry-standard way to refer to those belonging to this category. It is usually referred to as simply "Windows application". However, in order to distinguish it more clearly from other types (Windowless Window application and Dialog-based Windows application), I added the word "regular".

Windows applications that do not belong to this category include Calculator, Volume Control Panel, and many Control Panel Applet (small applications that are in Control Panel), categorized under "Dialog-Based Windows applications". In addition, Service (NT Service) applications also do not belong to "Regular Windows Application", but we will not discuss service in this course.

SimpleApp

I wrote this program as an example, but usually you would use Visual C++ AppWizard to generate similar bare-minimum application, which we will discuss later in this section.

The functionality of SimpleApp program is very minimal: it shows a window with a menu, from which you can tell it to show "About dialog box" and exit from the application. In contrast to SkeledonNW application that we saw in the previous section, this program shows a window. This simple difference is significant when you see the code.

SkeletonApp

This program is a pure Windows application that displays a window. Visual C++ AppWizard automatically generated all files for this project.

File generated by AppWizard

As you can see, it generates several source files for you. All files are complete and you can build and run the program without any modification. It is written in C, and does not use C++ nor any MFC feature. This AppWizard generated application is a good starting point for your own programs.

Event-driven execution model

Comparing the with sequential execution mode we discussed in the previous section. Unlike a typical C program, in which a program execution is top down, event-driven execution model heavily relies on "event handler". In essence, the program sets up a loop to listen to an event. When the event is of your interest, it invokes a corresponding event handler. Windows programming is all about "event handling". This is another reason why beginner Windows programmers get easily confused: it is not like typical C program they have been writing.

Dialog-Based Windows Application