By Karen Kenworthy

DEEP INSIDE YOUR PC, stealth programs and other unseen visitors are carrying out secret missions. Wouldn't you sleep-and work-better if you could keep an eye on these strangers?

It doesn't take a private eye to keep tabs on your Windows programs. Windows maintains a so-called Master List with information about all open windows, visible and invisible. By sneaking a peek at this list, you can learn what's happening inside your PC. And with a little help, you'll gain more control over your applications.

Bill Gates had a reason for naming his favorite operating system family Windows. Every program running under Windows 95, 3.1x or NT must open at least one window, even if you never see it on screen. Likewise, every program triggers at least one entry in the Master List.

Using the list, you can create an audit file showing all the programs you've run, and the start and stop time for each. Or you could build a program that prevents you from launching more than one copy of a particular application. The catch is finding a way to view the Master List.

Windows executes a loop for each entry in the Master List. Each time through the loop, the variable WndHnd contains the handle of a different window. The loop is where the GetMasterList function performs its heavy lifting. It's carried out in lines 7 through 15.

Line 7 passes WndHnd to the Windows API function GetWindowTextLength to determine the number of characters in the window's title bar. This value is then stored in the variable named TextLen.

The If statement in line 8 tests the value of TextLen. If TextLen is zero, indicating a blank window title, the program skips directly to line 13. This AddItem statement adds a line to the list box lbTasks, which contains only the window's handle, and the special string <no title>.

If TextLen is greater than zero, however, lines 9 through 11 are executed. First, the variable named WndTitle (window title) is initialized, ensuring the variable is large enough to hold the window's title text. As a precaution, allow for one more character than GetWindowText Length reports.

Line 10 is where you call the Windows API function GetWindowText and obtain the actual title text. This function requires three parameters: the handle of the window whose text is being retrieved, the variable where the text should be stored and a figure indicating the maximum number of characters that can be stored in parameter two. Next, in line 11, the AddItem statement adds a line containing the window's handle and title text to the list box lbTasks.

Finally, in line 15, you add one to your window counter. Because the counter has the same name as the function (GetMasterList), this value will be returned to statements elsewhere in our program that call GetMasterList.

Where do you go from here? As I hinted earlier, you can use GetMasterList to create several helpful programs. Create an audit file showing all programs run, and the start and stop time for each. Or use GetMasterList to build a program that prevents you from launching more than one copy of a particular application. If this program detects the launch of a second copy of an application, it activates the original copy instead.

I may return to GetMasterList and examine some of these possibilities in detail in a later column. Until then, don't hold back! Drop me a note if you find a use for GetMasterList you'd like to share.