C / C++ / MFC

Re: How to access HKEY_CURRENT_USER from local system account?

29-Mar-06 1:54

Hi together,

I have a big problem. I hope somebody can help me:

I implemented a service that runs under the local system account and checks if any screen blanker is activated. I use the following code:

bool result = false;
SystemParametersInfo(SPI_GETSCREENSAVEACTIVE, 0, (LPVOID) &result, 0);

This works fine on Win XP, but on Win 2000 the function always return true. It is a known bug according to article number 318781 on MSDN.

The suggested workaround is to look for the entry "SCRNSAVE.EXE" under the registry key "HKCU\Control Panel\Desktop" using the following two lines:

RegOpenKeyEx(HKEY_CURRENT_USER, "Control Panel\\Desktop", 0, KEY_READ, &hKeyScrSave);
RegQueryValueEx(hKeyScrSave, "SCRNSAVE.EXE", NULL, NULL, (LPBYTE) szData, &dwData);

Now the problem arises: As my service runs under the local system account, access to "HKEY_CURRENT_USER" is redirected to "HKEY_USERS\.DEFAULT". Dead | X|

So the result refers to the logon screen saver, which is (usually) always activated. But I only want this result if no user in logged in.

Therefore my question: Does anybody has a solution, how to check if a screen saver is active under 2000 like SystemParametersInfo(SPI_GETSCREENSAVEACTIVE) does it for XP? An idea how to access data under "HKEY_CURRENT_USER" from the local system account would also be very valuable for me.

Thank you very much for any hints,
Marcus.

James R. Twine29-Mar-06 2:49

James R. Twine

29-Mar-06 2:49

   Two quick things - first SystemParametersInfo(...) does not use C++ types, so you should be passing the address of a BOOL (an int, or 4-bytes under 32-bit MS), not a bool (1-byte under 32-bit MS).

   Second, I am pretty sure that screen savers run on a separate desktop, the "screen saver desktop". Search MSDN for information on Window Stations and Desktops for more information.

   If I am correct, you might be able to determine which desktop is active, and from that determine if a screen saver is running.

   Peace!

-=- James

If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
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Re: How to access HKEY_CURRENT_USER from local system account?

khb29-Mar-06 3:08

Re: How to access HKEY_CURRENT_USER from local system account?

29-Mar-06 3:08

Hi James,

thank you very much for your reply!

Concerning the bool/BOOL issue: I'm actually using a BOOL. In my message, however, I cut & pasted the code from MSDN, which seems to contain several bugs/typos Frown | :(

Anyway, thanks for the hint.

Concerning the desktop issue: I think you are right. Some time ago I've read that the screen saver runs on another desktop. So I'll dig into that again Wink | ;)

Thank you again,
Marcus.

David Crow29-Mar-06 3:16

David Crow

29-Mar-06 3:16

khb wrote:
SystemParametersInfo(SPI_GETSCREENSAVEACTIVE, 0, (LPVOID) &result, 0);

I think you want to check SPI_GETSCREENSAVERRUNNING instead.

khb wrote:
Now the problem arises: As my service runs under the local system account, access to "HKEY_CURRENT_USER" is redirected to "HKEY_USERS\.DEFAULT".

See MSDN article Q168877 for an example.

"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

Re: How to access HKEY_CURRENT_USER from local system account?

khb29-Mar-06 3:29

Can I return an array of pointers of type unsigned char[]

29-Mar-06 3:29

Hi David,

I think that what I posted was correct. I want to check if a user has "installed" a screen saver so that I can expect that there is a change that it will start running somewhen. Anyway, I check if it is actually running, too.

The howto on Q168877 seems to be exactly what I was looking for, great!

Thank you,
Marcus.

Laughing Buddha29-Mar-06 1:52

Laughing Buddha

29-Mar-06 1:52

Hi,

I am creating an array of pointers that point to unsigned char arrays like so

unsigned char* data[3];

where
data[0] = new unsigned char[256];
data[1] = new unsigned char[256];
data[2] = new unsigned char[256];

I now want to return this pointer array data from one function. How can I do that? Or what way could I return data[0], data[1] and data[2]?

Thanks for any help cause am a bit stuck here

Re: Can I return an array of pointers of type unsigned char[]

Stephen Hewitt29-Mar-06 1:55

Re: Can I return an array of pointers of type unsigned char[]

29-Mar-06 1:55

You can't return an array - If you burry it in a stuct you can work around this. i.e.

struct MyData
{
     unsigned char* data[3];
};
 
// Now return the struct instead.
MyData Function()
{
     MyData md;
     // Blah blah blah...
     return md;
}

Steve

Laughing Buddha29-Mar-06 2:09

Laughing Buddha

29-Mar-06 2:09

Oh ok! Thanks.
I will call that function in a different class though. So do I have to define another struct (lets call it MyData') and then lets say

void callFunction

{
md'.data[3]=Class::Function;
...}

How would I go about getting data[0], data[1] and data[2] then? Sorry just a bit confused as its like arrays, pointers and structs and am quite new to this.

Thanks in advance for any help!

Re: Can I return an array of pointers of type unsigned char[]

Stephen Hewitt29-Mar-06 2:12

Re: Can I return an array of pointers of type unsigned char[]

29-Mar-06 2:12

Code like this:

MyData d1, d2;
// Blah blah blah...
d1 = d2;

Copies dt.data[0], dt.data[1] and dt.data[2] (and all the rest if any).

Steve

toxcct29-Mar-06 2:38

Re: Can I return an array of pointers of type unsigned char[]

29-Mar-06 2:38

you'll have to create the MyData::operator = () member for this, otherwise, it will only copy the addresses, not the array contents...

Stephen Hewitt29-Mar-06 2:40

Re: Can I return an array of pointers of type unsigned char[]

29-Mar-06 2:40

The question said, "return this pointer array" - I believe it's the addresses that he wants copied - Although it wasn't clearly stated.

Steve

toxcct29-Mar-06 2:42

Re: Can I return an array of pointers of type unsigned char[]

29-Mar-06 2:42

Stephen Hewitt wrote:
Although it wasn't clearly stated

agreed

toxcct29-Mar-06 2:34

Re: Can I return an array of pointers of type unsigned char[]

29-Mar-06 2:34

your code is incorrect because you return a local object...

>> You can't return an array
yes we can, by returning the pointer... it is exactly the same when you pass arrays as parameters to functions.

Stephen Hewitt29-Mar-06 2:43

Re: Can I return an array of pointers of type unsigned char[]

29-Mar-06 2:43

v2.0 wrote:
your code is incorrect because you return a local object...

No I don't - I return a copy of a local object - This is fine. Returning a pointer or reference to a local object is where you get into trouble.

v2.0 wrote:
>> You can't return an array
yes we can, by returning the pointer... it is exactly the same when you pass arrays as parameters to functions.

Returning a pointer is not the same as returning an array - A process called "decay" occurs and you lose the size info. With the code I gave (array in a struct) an array is returned and no decay occurs and the length is not lost - But the data is copied not referenced.

Steve

James R. Twine29-Mar-06 2:59

James R. Twine

29-Mar-06 2:59

Stephen Hewitt wrote:
A process called "decay" occurs and you lose the size info

Not just that, but you also effectively change the type of the variable - an array is generally a valid location in memory (whose location cannot be changed easily), while a pointer can point to a valid location in memory. (This difference is also important when optimizing code.)

Peave!

-=- James

Re: Can I return an array of pointers of type unsigned char[]

Rage29-Mar-06 2:57

Rage

29-Mar-06 2:57

Since you have to put the returned array in an array anyway, you can create this "reception" array before calling the function and pass it as a parameter to the function. I think this is a much better solution than trying to "return" it, even burried in a struct. Unsure | :~

~RaGE();

Re: Can I return an array of pointers of type unsigned char[]

toxcct29-Mar-06 3:07

Re: Can I return an array of pointers of type unsigned char[]

29-Mar-06 3:07

ahhhh, good ol' C runtime Jig | [Dance]

Well done Mr "Diplomacy" Wink | ;)

Rage29-Mar-06 23:04

Rage

29-Mar-06 23:04

V2.0 is too much for me. I'll go back to V1.6.

~RaGE();

Re: Can I return an array of pointers of type unsigned char[]

toxcct29-Mar-06 23:07

29-Mar-06 23:07

v3.0 release date is set to 02/05/06... don't forget it Wink | ;)

Tetris C++ Code

v1raj29-Mar-06 1:41

v1raj

29-Mar-06 1:41

Hi i am doing a project and am making a tetris game in C++ V 6.0. So far i have crated the main menu screen... now i need to draw out a grid and start to make shapes fall... it seems i dont know how to do this. Does anyone have any tips or any codes i could have a look at??

Cheers for the help guys!

Re: Tetris C++ Code

Cedric Moonen29-Mar-06 1:47

Cedric Moonen

29-Mar-06 1:47

The best option is probably to create a custom control and do all the drawing yourself. Take a look at the miscellaneous controls on this site to see how to make one (it is not easy). Then to make the shapes fall, I think a timer will do that.

Re: Tetris C++ Code

khb29-Mar-06 2:02