Win32 API question...GetLogicalDrives...

[Nooze2k]

I have a Win32 assignment due in a few weeks, but I thought I'd get a jump start on it anyways. I keep running into a stupid problem with it though. One of the requirements is to use the GetLogicalDrives function to obtain a list of what drives are currently installed on someones system. However, we aren't being shown how to do so my my prof. I think I've made some leeway (I can get the function to return value into an unsigned long variable.) However, the return value of the function is a bitwise operator. This is where I get stumped. Any help would be greatly appreciated as the MS help files don't help worth squat.

[Boner]

Here's an example:

http://www.partware.com/ebooks/api/r...caldrives.html

Here's a Google Groups thread that may help also:

http://groups.google.com/groups?hl=e...t-ops.be#link1

[twister002]

From what I remember, I'm off in .NET land now, you AND out the drives you want to check for.

drive A: = 1
drive B: = 2

If there aren't any (in other words the method fails for some reason) it returns 0 and you have to go hunting for the last error.

I think in .NET it returns a string array of the drive letters, similar to GetLogicalDriveStrings in the Win32 API.

[charliex]

basically each bit in the 32 bit return value is set to 1 if a drive exists, and each bit position corresponds to a drive letter

all you have to do is, test the bit position corresponding to the drive letter to determine if it exists.


In C you could use a bitfield and let the compiler handle all the tests for you. either otherwise its simply doing an and with a 1&lt&ltbit_number where the first is drive A.

val = GetLogicalDrives( );
	for(i=0;i&lt26;i++) {
		printf("drive %c: is %s\n", i+'A',ret&(1&lt&lti)?"Available" : "Not Available");
	}

thatd list if the drive is available or not (barring typos)

[Nooze2k]

Thanks all for the info. We're going to be doing alot of MFC and .NET next semester (in May since I have co-op jan-apr), so they want us to have the fundamentals first. I'll try these out and let you know if they fix my problem!

[Nooze2k]

Its working! This is the code I'm using (far from final.... just using it to test the function).... So far, it outputs no problem.)

DWORD logicalDrives = GetLogicalDrives() << 1;
int i = 1;
char driveLetter = 'A';
string drive;

while(logicalDrives)
{
if(logicalDrives & (int)pow(2,i))
{
drive = driveLetter;
MessageBox(hWnd, drive.c_str(), "test", 0);
}

++i;
++driveLetter;

}


Seems a lil archaic, but it was just to see if it works, which it does! It still locks up after the last drive which I expected since its searching for drives which don't exist. That should be simple enough to fix. When I'm finished, I'll have all the info for the drive (letter, type, size, etc) all in either a struct or class. Everything should be smooth sailing form here on. I'm actually quite pleasantly surprised how easy it was to solve, just haven't used Bitwise operators much yet. Thanks all for your help though. Muchly appreciated!

[charliex]

your code seems to have some mistakes in it

while( logicalDrives ) ? what did you intend with this, nothing happens to logicalDrives in the loop, you might have meant an if instead, then a loop for 26 for all drive letters

why are you shifting the result ?

1 << i is the same as pow(2,i)

not sure if you are using ++i just as a style choice, but theres no difference between ++i and i++ in your context

[Nooze2k]

++i is just a style choice (habit I guess since I'm not doing anything before the increment).... I shifted it because it wasn't displaying my drives properly. I have c,d and e installed, but without shifting it showed b,c, & d.... shifting fixed it
I also changed "while(logicaldrives)" to "while(driveletter <= 'Z')" This ensured it would look for all drive letters from A-Z, plus fixed the error of searching for unknown drives.