This article was previously published under Q123871
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You may run into problems when debugging screen saver type applications in the Visual C++ development environment. For example, when attempting to debug the SCRNSAVE application included with Visual C++ version 2.0, the program starts correctly, but then may fail to return control and the focus to the debugger.
This is expected behavior. Screen savers don't use the same desktop as normal applications. When a breakpoint in the screen saver is encountered, the operating system doesn't switch desktops. Thus, there may be no screen in which to display the Visual C++ user interface and the breakpoint is essentially ignored.
There are two possible workarounds to this problem:
Try debugging your application without using the Always-on-Top feature. Add the feature when the application is ready to be released.
Use remote debugging. For more information on remote debugging, see the "Debugging Remote Applications" section in the "Using The Debugger" chapter of the "Visual C++ User's Guide," or search for "remote debugging," in the Visual C++ Books Online.
Steps to Reproduce Behavior
Using the Visual C++ version 2.0 SCRNSAVE sample in the \MSVC20\SAMPLES\WIN32\SCRNSAVE directory on the distribution CD, do the following:
Build the program with debug information.
Set a breakpoint on line 73 of FRACTAL.C.
Set /S as an option for FRACTAL.EXE. To do this, select Settings from the Project menu. Then select the Debug sheet from the Settings dialog. Type "/S" (without the quotation marks) on the Program Arguments line.
Run the program by pressing the F5 key. The screen should turn black and appear to hang. Bring up the Task List by pressing CTRL+ESC. Then quit Visual C++ to regain control of the system.
NOTE: The SCRNSAVE sample included with Visual C++ version 4.0 is entirely different from that of Visual C++ version 2.0; it demonstrates Control Panel utility library routines for managing "cpArrow" window class/spinner controls used in applet dialog boxes.
NOTE: No screen saver sample is provided in Visual C++ .NET.
9.00 Always Top HWND_TOP hung frozen not responding