Using CreateFile to create a handle for a USB device on 64 bit OS

Question

I have the following code used to create a valid handle using CreateFile working on a 32 bit XP OS. When testing the same code on a 64 bit Vista and Windows 7 computer, CreateFile returns an invalid handle value. I can not seem to figure out what is going on.

Here is the dll import:

[DllImport("kernel32.dll", SetLastError = true)]
static extern IntPtr CreateFile(
     string FileName,
     uint DesiredAccess,
     uint ShareMode,
     IntPtr SecurityAttributes,
     uint CreationDisposition,
     uint FlagsAndAttributes,
     IntPtr hTemplateFile
     );

And the call:

drive = CreateFile(devicePath,
           GENERIC_READ | GENERIC_WRITE,
           FILE_SHARE_READ | FILE_SHARE_WRITE,
           IntPtr.Zero,
           OPEN_EXISTING,
           FILE_FLAG_DELETE_ON_CLOSE,
           IntPtr.Zero);

devicePath is a valid path to the usb. This returns a valid handle on a 32 bit OS and an invalid value on a 64 bit OS. I have searched and searched and found nothing. If anyone could help or share some information I would be thankful. Regards.

@pstrjds Compiling for x86 is the opposite of what he should be doing. `CreateFile` returns `HANDLE`, which is `PVOID`, also known as `void*`. On a 64-bit OS, the returned value should be 64-bit. — Polynomial, Aug 01 '12 at 15:37
@Polynomial - Yeah, I realized that I had inverted my logics after I typed it, which is why I deleted my comment :) — pstrjds, Aug 01 '12 at 15:49
In the 64 bit OS when you are getting a -1, have you checked what the last error was. Maybe you are running into some UAC permission type issue on your 64 bit OS. — pstrjds, Aug 01 '12 at 15:56
that seems to be the case, thank you. I get error code 5, access denied — daniel, Aug 01 '12 at 16:09

score 2 · Answer 1 · edited May 23 '17 at 10:32

2

Verify that you're compiling for AnyCPU. If you compilation target is x86, you'll have 32-bit IntPtr types on both 32-bit and 64-bit operating systems. Compiling for AnyCPU allows the IntPtr data type to reflect the size of a pointer.

The CreateFile API returns HANDLE, which is an alias for PVOID (a.k.a. void*), so it'll be 64 bits long on a 64-bit OS, and 32 bits long on a 32-bit OS.

When you compile for x86, the code expects a 32-bit value to be returned by the API. Since it's actually 64-bit, you lose half of it, giving you an invalid pointer.

edited May 23 '17 at 10:32

Community

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answered Aug 01 '12 at 15:36

Polynomial

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it does compile in x86 and yields a 32 bit type. on x64 it returns a -1 – daniel Aug 01 '12 at 15:39
@dechiada In Visual Studio, go to Build -> Configuration Manager, and set the Active Solution Platform dropdown at the top to Any CPU. – Polynomial Aug 01 '12 at 15:42
Go to Project -> Properties, then look in the Build tab. Under Platform Target, check that it's set to Any CPU. – Polynomial Aug 01 '12 at 15:46
It is also set to any CPU there – daniel Aug 01 '12 at 15:49
Odd. Please verify that `IntPtr.Size` is 8 on the 64-bit system. – Polynomial Aug 01 '12 at 15:53

score 0 · Answer 2 · answered Nov 03 '16 at 04:45

It's worth mentioning (since so many people get it wrong) that on 64-bit Windows, handles may safely be truncated to 32 bits.

This allows the handles to be compatible with 32-bit applications (but not 16-bit applications) without special "handle transform" thunking.

Going the other way, truncated 32 bit handles may be safely sign extended to 64 bits. (The invalid handle -1 must by sign extended)

MSDN "Running 32-bit Applications" "handles have 32 significant bits on 64-bit Windows."

Using CreateFile to create a handle for a USB device on 64 bit OS

2 Answers2