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Creating Win32 Applications (C++)

Updated: July 2009

The Win32 API (also known as the Windows API) is a C-based framework for creating Windows applications, and has been around since Windows 1.0. Extensive documentation for this API can be found at Windows API.

In this procedure, we create a simple Win32 application that displays "Hello, World!" to a window. The procedure steps are identical for all Win32 applications. After you complete this procedure, you can use the code that you created here as a skeleton to create any other Win32 application.

This topic assumes that you understand the fundamentals of the C++ language.

link to video For a video version of this topic, see Video How to: Creating Win32 Applications (C++).

To create a new Win32 project

  1. On the File menu, click New, and then click Project....

  2. In the Project Types pane, select Win32 in the Visual C++ node, and then select Win32 Project in the Templates pane.

    Type a name for the project, such as win32app. You can accept the default location, type a location, or browse to a directory where you want to save the project.

  3. On the Win32 Application Wizard, select Next.

  4. On the Win32 Application Wizard, under Application type select Windows application. Under Additional options select Empty project. Leave the remaining options as they are. Click Finish to create the project.

  5. Add a C++ file to the project by selecting Add New Item... from the Project menu. In the Add New Item dialog box, select C++ File (.cpp). Type a name for the file, such as GT_HelloWorldWin32.cpp, and click Add.

To start a Win32 applications

  1. As you know, every C and C++ application must have a main function. This function is the starting point for the application. Similarly, in a Win32 application, every application must have a WinMain function. The syntax for WinMain is as follows:

    int WINAPI WinMain(HINSTANCE hInstance,
                       HINSTANCE hPrevInstance,
                       LPSTR lpCmdLine,
                       int nCmdShow);
    

    For an explanation of the parameters and return value of this function, see WinMain Function.

  2. Since application code must use existing definitions, you should add include statements to use them. For example:

    #include <windows.h>
    #include <stdlib.h>
    #include <string.h>
    #include <tchar.h>
    
  3. In addition to WinMain, each Win32 application must also have a second function which is usually called WndProc, which stands for window procedure. The syntax for WndProc is as follows:

    LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
    

    The purpose of this function is to handle any messages that your application receives from the operating system. When does your application receive messages from the operating system? All the time! For example, imagine that we have created a dialog box that has an OK button. When the user clicks that button, the operating system sends our application a message, which lets us know that a user pressed this button. The WndProc function is responsible for responding to that event. In our example, the appropriate response might be to close the dialog box.

    For more information, see Window Procedures.

To add functionality to WinMain

  1. First, create inside the WinMain function a window class structure of type WNDCLASSEX. This structure contains information about your window, such as the application's icon, the background color of the window, the name to display in the title bar, the name of the window procedure function, and so on. A typical WNDCLASSEX structure follows:

        WNDCLASSEX wcex;
    
        wcex.cbSize = sizeof(WNDCLASSEX);
        wcex.style          = CS_HREDRAW | CS_VREDRAW;
        wcex.lpfnWndProc    = WndProc;
        wcex.cbClsExtra     = 0;
        wcex.cbWndExtra     = 0;
        wcex.hInstance      = hInstance;
        wcex.hIcon          = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_APPLICATION));
        wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);
        wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
        wcex.lpszMenuName   = NULL;
        wcex.lpszClassName  = szWindowClass;
        wcex.hIconSm        = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_APPLICATION));
    

    For an explanation of the fields of this structure, see WNDCLASSEX.

  2. Now that you have created your window class, you must register it. Use the RegisterClassEx function, and pass the window class structure as an argument:

        if (!RegisterClassEx(&wcex))
        {
            MessageBox(NULL,
                _T("Call to RegisterClassEx failed!"),
                _T("Win32 Guided Tour"),
                NULL);
    
            return 1;
        }
    
  3. Now that you have registered your class, it is time to create a window. Use the CreateWindow function as follows:

    static TCHAR szWindowClass[] = _T("win32app");
    static TCHAR szTitle[] = _T("Win32 Guided Tour Application");
    // The parameters to CreateWindow explained:
    // szWindowClass: the name of the application
    // szTitle: the text that appears in the title bar
    // WS_OVERLAPPEDWINDOW: the type of window to create
    // CW_USEDEFAULT, CW_USEDEFAULT: initial position (x, y)
    // 500, 100: initial size (width, length)
    // NULL: the parent of this window
    // NULL: this application dows not have a menu bar
    // hInstance: the first parameter from WinMain
    // NULL: not used in this application
    HWND hWnd = CreateWindow(
        szWindowClass,
        szTitle,
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT,
        500, 100,
        NULL,
        NULL,
        hInstance,
        NULL
    );
    if (!hWnd)
    {
        MessageBox(NULL,
            _T("Call to CreateWindow failed!"),
            _T("Win32 Guided Tour"),
            NULL);
    
        return 1;
    }
    

    This function returns an HWND, which is a handle to a window. For more information, see Windows Data Types.

  4. Now that we have created the window, we can display it to the screen using the following code:

    // The parameters to ShowWindow explained:
    // hWnd: the value returned from CreateWindow
    // nCmdShow: the fourth parameter from WinMain
    ShowWindow(hWnd,
        nCmdShow);
    UpdateWindow(hWnd);
    

    So far, this window will not display much, because we have not yet implemented the WndProc function.

  5. The final step of WinMain is the message loop. The purpose of this loop is to listen for messages that the operating system sends. When the application receives a message, the message is dispatched to the WndProc function to handle it. The message loop resembles this:

        MSG msg;
        while (GetMessage(&msg, NULL, 0, 0))
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
    
        return (int) msg.wParam;
    

    For more information about the structures and functions that is used in the message loop, see MSG, GetMessage, TranslateMessage, and DispatchMessage.

    The steps that you have just completed are common to most Win32 applications. For include directives and global variable declarations required in this application, see the complete code example at the end of this topic.

    At this point, your WinMain function should resemble this:

    int WINAPI WinMain(HINSTANCE hInstance,
                       HINSTANCE hPrevInstance,
                       LPSTR lpCmdLine,
                       int nCmdShow)
    {
        WNDCLASSEX wcex;
    
        wcex.cbSize = sizeof(WNDCLASSEX);
        wcex.style          = CS_HREDRAW | CS_VREDRAW;
        wcex.lpfnWndProc    = WndProc;
        wcex.cbClsExtra     = 0;
        wcex.cbWndExtra     = 0;
        wcex.hInstance      = hInstance;
        wcex.hIcon          = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_APPLICATION));
        wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);
        wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
        wcex.lpszMenuName   = NULL;
        wcex.lpszClassName  = szWindowClass;
        wcex.hIconSm        = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_APPLICATION));
    
        if (!RegisterClassEx(&wcex))
        {
            MessageBox(NULL,
                _T("Call to RegisterClassEx failed!"),
                _T("Win32 Guided Tour"),
                NULL);
    
            return 1;
        }
    
        hInst = hInstance; // Store instance handle in our global variable
    
        // The parameters to CreateWindow explained:
        // szWindowClass: the name of the application
        // szTitle: the text that appears in the title bar
        // WS_OVERLAPPEDWINDOW: the type of window to create
        // CW_USEDEFAULT, CW_USEDEFAULT: initial position (x, y)
        // 500, 100: initial size (width, length)
        // NULL: the parent of this window
        // NULL: this application dows not have a menu bar
        // hInstance: the first parameter from WinMain
        // NULL: not used in this application
        HWND hWnd = CreateWindow(
            szWindowClass,
            szTitle,
            WS_OVERLAPPEDWINDOW,
            CW_USEDEFAULT, CW_USEDEFAULT,
            500, 100,
            NULL,
            NULL,
            hInstance,
            NULL
        );
    
        if (!hWnd)
        {
            MessageBox(NULL,
                _T("Call to CreateWindow failed!"),
                _T("Win32 Guided Tour"),
                NULL);
    
            return 1;
        }
    
        // The parameters to ShowWindow explained:
        // hWnd: the value returned from CreateWindow
        // nCmdShow: the fourth parameter from WinMain
        ShowWindow(hWnd,
            nCmdShow);
        UpdateWindow(hWnd);
    
        // Main message loop:
        MSG msg;
        while (GetMessage(&msg, NULL, 0, 0))
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
    
        return (int) msg.wParam;
    }
    

To add functionality to WndProc

  1. The purpose of the WndProc function is to handle messages that your application receives. You usually implement this by using a switch function.

    The first message we will handle is the WM_PAINT message. Your application receives this message when a portion of your application's window must be updated. When a window is first created, the whole window must be updated, and this message is passed to indicate this.

    The first thing that you should do when you handle a WM_PAINT message is call BeginPaint, and the last thing that you should do is call EndPaint. In between these two function calls you handle all the logic to lay out the text, buttons, and other controls for your window. For this application, we display the string "Hello, World!" inside the window. To display text, use the TextOut function, as shown here:

    PAINTSTRUCT ps;
    HDC hdc;
    TCHAR greeting[] = _T("Hello, World!");
    
    switch (message)
    {
    case WM_PAINT:
        hdc = BeginPaint(hWnd, &ps);
    
        // Here your application is laid out.
        // For this introduction, we just print out "Hello, World!"
        // in the top left corner.
        TextOut(hdc,
            5, 5,
            greeting, _tcslen(greeting));
        // End application-specific layout section.
    
        EndPaint(hWnd, &ps);
        break;
    }
    
  2. Your application will typically handle many other messages, such as WM_CREATE and WM_DESTROY. A simple but complete WndProc function follows:

    LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
    {
        PAINTSTRUCT ps;
        HDC hdc;
        TCHAR greeting[] = _T("Hello, World!");
    
        switch (message)
        {
        case WM_PAINT:
            hdc = BeginPaint(hWnd, &ps);
    
            // Here your application is laid out.
            // For this introduction, we just print out "Hello, World!"
            // in the top left corner.
            TextOut(hdc,
                5, 5,
                greeting, _tcslen(greeting));
            // End application specific layout section.
    
            EndPaint(hWnd, &ps);
            break;
        case WM_DESTROY:
            PostQuitMessage(0);
            break;
        default:
            return DefWindowProc(hWnd, message, wParam, lParam);
            break;
        }
    
        return 0;
    }
    

Description

After you completed all the steps, your code should resemble the following. To build the application, select Build Solution from the Build menu. If your application compiles without any errors, you can run the application by pressing F5. A simple window with the text "Hello, World!" will be displayed on the screen near the upper-left corner.

Code

// GT_HelloWorldWin32.cpp
// compile with: /D_UNICODE /DUNICODE /DWIN32 /D_WINDOWS /c

#include <windows.h>
#include <stdlib.h>
#include <string.h>
#include <tchar.h>

// Global variables

// The main window class name.
static TCHAR szWindowClass[] = _T("win32app");

// The string that appears in the application's title bar.
static TCHAR szTitle[] = _T("Win32 Guided Tour Application");

HINSTANCE hInst;

// Forward declarations of functions included in this code module:
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain(HINSTANCE hInstance,
                   HINSTANCE hPrevInstance,
                   LPSTR lpCmdLine,
                   int nCmdShow)
{
    WNDCLASSEX wcex;

    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.style          = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc    = WndProc;
    wcex.cbClsExtra     = 0;
    wcex.cbWndExtra     = 0;
    wcex.hInstance      = hInstance;
    wcex.hIcon          = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_APPLICATION));
    wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
    wcex.lpszMenuName   = NULL;
    wcex.lpszClassName  = szWindowClass;
    wcex.hIconSm        = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_APPLICATION));

    if (!RegisterClassEx(&wcex))
    {
        MessageBox(NULL,
            _T("Call to RegisterClassEx failed!"),
            _T("Win32 Guided Tour"),
            NULL);

        return 1;
    }

    hInst = hInstance; // Store instance handle in our global variable

    // The parameters to CreateWindow explained:
    // szWindowClass: the name of the application
    // szTitle: the text that appears in the title bar
    // WS_OVERLAPPEDWINDOW: the type of window to create
    // CW_USEDEFAULT, CW_USEDEFAULT: initial position (x, y)
    // 500, 100: initial size (width, length)
    // NULL: the parent of this window
    // NULL: this application dows not have a menu bar
    // hInstance: the first parameter from WinMain
    // NULL: not used in this application
    HWND hWnd = CreateWindow(
        szWindowClass,
        szTitle,
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT,
        500, 100,
        NULL,
        NULL,
        hInstance,
        NULL
    );

    if (!hWnd)
    {
        MessageBox(NULL,
            _T("Call to CreateWindow failed!"),
            _T("Win32 Guided Tour"),
            NULL);

        return 1;
    }

    // The parameters to ShowWindow explained:
    // hWnd: the value returned from CreateWindow
    // nCmdShow: the fourth parameter from WinMain
    ShowWindow(hWnd,
        nCmdShow);
    UpdateWindow(hWnd);

    // Main message loop:
    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return (int) msg.wParam;
}

//
//  FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  PURPOSE:  Processes messages for the main window.
//
//  WM_PAINT    - Paint the main window
//  WM_DESTROY  - post a quit message and return
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    PAINTSTRUCT ps;
    HDC hdc;
    TCHAR greeting[] = _T("Hello, World!");

    switch (message)
    {
    case WM_PAINT:
        hdc = BeginPaint(hWnd, &ps);

        // Here your application is laid out.
        // For this introduction, we just print out "Hello, World!"
        // in the top left corner.
        TextOut(hdc,
            5, 5,
            greeting, _tcslen(greeting));
        // End application-specific layout section.

        EndPaint(hWnd, &ps);
        break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
        break;
    }

    return 0;
}

Date

History

Reason

July 2009

Added information about include directives and global variable declarations.

Customer feedback.

January 2010

Added mention of include statements earlier in the material.

Customer feedback.

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