A progress bar is a window that an application can use to indicate the progress of a lengthy operation. It consists of a rectangle that is animated as an operation progresses.

The following illustration shows a progress bar that does not use visual styles.

More information is contained under the following headings.

• Using Progress Bars
  • Range and Current Position
  • Default Progress Bar Message Processing
  • Marquee Style
  • Progress Bar Example

Using Progress Bars

You can create a progress bar by using the CreateWindowEx function, specifying the PROGRESS_CLASS window class. This window class is registered when the common controls DLL is loaded. For more information, see About Common Controls.

The control is also available in the Microsoft Visual Studio Toolbox, where it is called Progress Control.

Range and Current Position

A progress bar's range represents the entire duration of the operation, and the current position represents the progress that the application has made toward completing the operation. The window procedure uses the range and the current position to determine the percentage of the progress bar to fill with the highlight color. Because the range and current position values are expressed as unsigned integers, the highest possible range or current position value is 65,535.

The minimum value in the range can be from 0 to 65,535. Likewise, the maximum value can be from 0 to 65,535. If you do not set the range values, the system sets the minimum value to 0 and the maximum value to 100. You can adjust the range to convenient integers by using the PBM_SETRANGE message.

A progress bar provides several messages that you can use to set the current position. The PBM_SETPOS message sets the position to a given value. The PBM_DELTAPOS message advances the position by adding a specified value to the current position.

The PBM_SETSTEP message allows you to specify a step increment for a progress bar. Subsequently, whenever you send the PBM_STEPIT message to the progress bar, the current position advances by the specified increment. By default, the step increment is set to 10.

Default Progress Bar Message Processing

This section describes the messages handled by the window procedure for the PROGRESS_CLASS class.

Marquee Style

By creating the progress bar control with the PBS_MARQUEE style, you can animate it in a way that shows activity but does not indicate what proportion of the task is complete. The highlighted part of the progress bar moves repeatedly along the length of the bar. You can start and stop the animation, and control its speed, by sending the PBM_SETMARQUEE message. Marquee progress bars do not have a range or position.

The following illustration shows a progress bar in marquee mode. The highlighted part moves across the bar.

Progress Bar Example

The following example shows how to use a progress bar to indicate the progress of a lengthy file-parsing operation. The example creates a progress bar and positions it along the bottom of the parent window's client area. The height of the progress bar is based on the height of the arrow bitmap used in a scroll bar. The range is based on the size of the file divided by 2048, which is the size of each "chunk" of data read from the file. The example also sets an increment and advances the current position of the progress bar by the increment after parsing each chunk.

Security Alert  

Using the ReadFile function incorrectly can compromise the security of your application. For instance, in the following example function, ParseALargeFile, you should check to make sure that ReadFile reads all the requested data.

Also notice that the fourth parameter of CreateFile—(LPSECURITY_ATTRIBUTES)NULL—sets default security values. If you need specific security settings you must set the appropriate values in the structure's members. Call sizeof to set the correct size of the LPSECURITY_ATTRIBUTES structure. You should review Security Considerations: Microsoft Windows Controls before continuing.

// ParseALargeFile - parses a large file and uses a
// progress bar to indicate the progress of the
// parsing operation. 
// Returns TRUE if successful, or FALSE otherwise. 
// hwndParent - parent window of the progress bar. 
// lpszFileName - name of the file to parse. 
// 
// Global variable 
//     g_hinst - instance handle 

extern HINSTANCE g_hinst; 

BOOL ParseALargeFile(HWND hwndParent, LPTSTR lpszFileName) 
{ 
    RECT rcClient;  // Client area of parent window 
    int cyVScroll;  // Height of scroll bar arrow 
    HWND hwndPB;    // Handle of progress bar 
    HANDLE hFile;   // Handle of file 
    DWORD cb;       // Size of file and count of
    // bytes read 
    LPCH pch;       // Address of data read from
    // file 
    LPCH pchTmp;    // Temporary pointer 



    // Ensure that the common control DLL is loaded
    // and create a progress bar along the bottom of
    // the client area of the parent window. 
    // Base the height of the progress bar on the
    // height of a scroll bar arrow. 
    InitCommonControls(); 
    GetClientRect(hwndParent, &rcClient); 
    cyVScroll = GetSystemMetrics(SM_CYVSCROLL); 

    hwndPB = CreateWindowEx(0, PROGRESS_CLASS,
        (LPTSTR) NULL, WS_CHILD | WS_VISIBLE,
        rcClient.left, rcClient.bottom - cyVScroll, rcClient.right, cyVScroll, 
        hwndParent, (HMENU) 0, g_hinst, NULL);

    // Open the file for reading, and retrieve the
    // size of the file. 

    hFile = CreateFile(lpszFileName, GENERIC_READ,
        FILE_SHARE_READ, (LPSECURITY_ATTRIBUTES)
        NULL, OPEN_EXISTING,
        FILE_ATTRIBUTE_NORMAL, (HANDLE) NULL); 

    if (hFile == (HANDLE) INVALID_HANDLE_VALUE) 
        return FALSE; 

    cb = GetFileSize(hFile, (LPDWORD) NULL); 

    // Set the range and increment of the progress
    // bar. 

    SendMessage(hwndPB, PBM_SETRANGE, 0,
        MAKELPARAM(0, cb / 2048)); 
    SendMessage(hwndPB, PBM_SETSTEP, (WPARAM) 1, 0); 

    // Parse the file. 
    pch = (LPCH) LocalAlloc(LPTR, sizeof(char) *
        2048); 
    pchTmp = pch; 
    do { 
        ReadFile(hFile, pchTmp, sizeof(char) * 2048,
            &cb, 
            (LPOVERLAPPED) NULL);
        // TODO: Write an error handler to check that all the
        // requested data was read. 
        // Include here any code that parses the
        // file. 
        . 
        . 
        . 
        // Advance the current position of the
        // progress bar by the increment. 
        SendMessage(hwndPB, PBM_STEPIT, 0, 0); 
    } while (cb); 

    CloseHandle((HANDLE) hFile); 
    DestroyWindow(hwndPB);

    return TRUE; 
}