Getlocaldrives() error ? please help !

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If the function succeeds, the return value is a bitmask representing the currently available disk drives. Bit position 0 (the least-significant bit) is drive A, bit position 1 is drive B, bit position 2 is drive C, and so on.
If the function fails, the return value is zero. To get extended error information, call GetLastError.

Can anybody Give me an example of what does it mean ?
This is from GetLogicalDrives() functions of MSDN.

Thanks

how the code will look like. I am trying but can't figure it out. it output 116.

Why?

What I have tried:

Myself and StackOverflow. I don't know what is btimask and how to work with it.
Please help!

Posted 28-May-16 10:22am

Member 11346124

Updated 28-May-16 15:37pm

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2 solutions

Solution 1

In a loop, create a bit mask, which is equal to 1 << N, where N is a bit number; N=0 for A, N=1 for B, and so on.
If you perform bitwise operation AND (& operator) with the return value and the mask, you will return either 0 or, non-zero value. If this value is zero, the bit is clear (there is no such logical drive), otherwise it is set (the drive is present).

That's all.

Please see: http://www.cprogramming.com/tutorial/bitwise_operators.html[^].

—SA

Posted 28-May-16 15:32pm

Sergey Alexandrovich Kryukov

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

George Jonsson · Accepted Answer · 2016-05-28T15:37:00

C++

DWORD dwDriveBitMask = GetLogicalDrives();

The result is dwDriveBitMask = 116 on your machine.

What you do is to convert it to a binary sequence. This is the bit mask.

    MSB                                 LSB
116 = 00000000 00000000 00000000 01110100 (DWORD has four bytes)

As the three upper bytes are 0, we can ignore them in this case and list the lowest byte only.

LSB 0  -> No A drive
    0  -> No B drive
    1  -> Have C drive
    0  -> No D drive
    1  -> Have E
    1  -> Have F
    1  -> Have G
    0  -> No H

Then there is the matter what you want to do with it. As you don't tell us that I will just give a small example.
Let's say you want to check if drive F is present on the PC.
Then you need to mask out the bit that represents the F drive. You do this with the bitwise AND operator &.
First you need a test mask where only the bit for the F drive is set

00100000

then you AND the values

01110100 & 00100000 = 00100000

In C++ the code will be

C++

DWORD dwDriveBitMask = GetLogicalDrives();
DWORD dwMaskDriveF = 0x20 (00100000)
if (dwDriveBitMask & dwMaskDriveF)
{
    // Do something
}

Getlocaldrives() error ? please help !

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Getlocaldrives() error ? please help !

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