More Registry Trouble...

[mikeman118]

Hi,

I have one final question about doing stuff with the registry. I was trying to use the "RegQueryValueEx" function to get a value from the registry, but I can't seem to get it to work. Everything compiles just fine, however when I run I get a dialog box "Unhandled exception at 0x77dd7904 in Program_Name.exe: 0xC0000005: Access violation reading location 0x000000c8." I'm pretty sure the error is in how I'm trying to save the data, but nothing I try works. Here's what I did:

BYTE lb;
RegQueryValueExA(phKey, "password", NULL, NULL, &lb, (LPDWORD)200/*wasn't sure what to put here...*/);

I'm pretty sure the "&lb" part is what is causing the problem, however since I've never used the "LPBYTE" type before maybe it's not (why couldn't they just stick to using char arrays?). All of the keys and values exist, and even if they didn't it still shouldn't give me an error like this. Can anyone help? Thanks.

[Salem]

> (LPDWORD)200/*wasn't sure what to put here...*/
Interestingly, 200 is, wait for it, in hex, 0xc8.

> Access violation reading location 0x000000c8

My guess is have another read of MSDN to find out what parameters you need to pass. It would seem that you need to pass the address of some buffer or address of some variable.

Simply inventing values, and casting away all the warnings doesn't work.
http://msdn2.microsoft.com/en-us/library/ms724911.aspx

Perhaps something like

BYTE lb[200];
DWORD length = 200;
RegQueryValueExA(phKey, "password", NULL, NULL, &lb, &length);

Apparently, length is updated with the actual length of the data read from the registry.

[mikeman118]

Ah, thank you Salem. I had done all of that but had forgotten to change that to a variable. Many thanks. Hopefully this is my last question!

[Elysia]

When there is a "LP" prefix before something, that means it's expecting a pointer to a variable of type after the LP prefix. So don't cast to LPX - never ever do that. Very bad.
Also check msdn's docs - since they actually say which parameters go in and out. And if you check closely you can also read what you're supposed to pass. If it says "pointer to a variable" then you must pass a pointer (sometimes NULL is also acceptable).

[mikeman118]

Ok I'll make sure to do that from now on. Thanks for the advice!