To read/set a user screensaver on Windows, do I need to use system registry or SystemParametersInfo API? - c++

Question

There seems to be two methods of setting and getting a user screensaver parameters on a Windows platform:
1: Via the SystemParametersInfo() API:
//To read
SystemParametersInfo(SPI_GETSCREENSAVEACTIVE, 0, &bScreensaverAcrtive, NULL);
SystemParametersInfo(SPI_GETSCREENSAVETIMEOUT, 0, &nScreensaverTimeout, NULL);
//No API to get the screensaver file used
//To set
SystemParametersInfo(SPI_SETSCREENSAVEACTIVE, 0, bScreensaverAcrtive, NULL);
SystemParametersInfo(SPI_SETSCREENSAVETIMEOUT, 0, nScreensaverTimeout, NULL);
//No API to change the screensaver file
2: Through the system registry keys:
HKCU\Control Panel\Desktop - "ScreenSaveActive"
HKCU\Control Panel\Desktop - "ScreenSaveTimeOut"
HKCU\Control Panel\Desktop - "SCRNSAVE.EXE"
But since there're two competing methods that seem to do the same, what is the recommended way to use?
PS. I highly favor method #2 (or writing directly into registry) due to the following reasons:
A. If you read the explanation of a bug in the SPI_GETSCREENSAVEACTIVE flag, you'll see that MS themselves recommend to use registry.
B. If you read the documentation for the SPI_SETSCREENSAVEACTIVE and SPI_SETSCREENSAVETIMEOUT flags, there's this mystical line that says, "*If the machine has entered power saving mode or system lock state, an ERROR_OPERATION_IN_PROGRESS exception occurs.*" I first ignored this situation until it actually started happening on my test installation of Windows 8. This is the most asinine error, I should tell you. There's absolutely no graceful way of interpreting what it means or do any workaround (except, writing directly into the registry.)

Answer 1

Use the API. Asking that is like asking if you should wait for the traffic light to turn green before crossing the road. I won't call the cops if I see you crossing at red, but if you ask me, I'll tell you you have to wait. And you are the one taking the risk of bad things happening.
The API is documented, the registry locations are not. Microsoft is in no obligation to preserve the registry locations or their functionality.
The SPI_GETSCREENSAVEACTIVE flag affects Windows 2000. If you support Windows 2000 as a target platform, I would apply the registry read to that version only (OSVERSIONINFO.dwMajor=5, .dwMinor=0)
ERROR_OPERATION_IN_PROGRESS I'd try to figure out under what circumstances this happens (e.g. screensaver already active, or system about to enter a power saving state).
Generally, I'd find it questionable if activating / deactivating the screensaver is not at least related to a user action, in which case the system should be ready to accept a change.
What are you trying to achieve? Why do you need to modify screensaver activity? Maybe there's some better method to achieve your goal

Answer 2

Use the API. The registry format changes often.
As for the power state changes, screen savers are really a 20th century feature. Laptops turn off the screen entirely, for obvious reasons. In that power saving state SPI_SETSCREENSAVEACTIVE obviously should fail. Not a lot of interpreting to do.
So, check for GUID_VIDEO_POWERDOWN_TIMEOUT first.
edit
I just realized that Group Policy screensavers are also unlikely to be in the registry, and certainly would override HKCU. Not a real issue for Windows 2000, of course, but today the API method would be even more advisable. Of course, do realize that this is just another reason why SPI_SETSCREENSAVEACTIVE may return an error. Still an improvement over the registry approach, which fails silently in the presence of Group Policy.

Answer 3

"To set" above is incorrect. It should be:
//To set
SystemParametersInfo(SPI_SETSCREENSAVEACTIVE, bScreensaverAcrtive, NULL, NULL);
SystemParametersInfo(SPI_SETSCREENSAVETIMEOUT, nScreensaverTimeout, NULL, NULL);