Common gotchas when writing your own p/invoke

re: Common gotchas when writing your own p/invoke

Ben Voigt [C++ MVP] — Mon, 17 Aug 2009 23:22:15 GMT

Also, the part about C/C++ char being ANSI is just plain wrong. Win32 functions variously treat char strings as ANSI, the OEM code page, or any of a large number of other SBCS or MBCS formats.

re: Common gotchas when writing your own p/invoke

Ben Voigt [C++ MVP] — Mon, 17 Aug 2009 23:19:39 GMT

@Raymond: By that definition, C/C++ char is also a "Unicode character", since it stores UTF-8 code units just dandy. I agree that a pendantic definition of 'character' vs code-point vs whatever isn't needed, but "UTF-16" is in order to meaningfully describe the difference between C char, .NET System.Char === C# char, and gcc wchar32_t

re: Common gotchas when writing your own p/invoke

MadQ — Sun, 16 Aug 2009 13:13:19 GMT

@Nathan_works: Several years ago, I hand-rolled a large portion of the DirectShow API in C#. I needed the ability to manually build and manipulate filter graphs.

I also once wrote a pluggable protocol handler in C# (IInternetProtocol, etc.) to allow reading resources from .NET assemblies. Kinda like the res: protocol lets you read Win32 resources from executable files.

None of this would have been possible without InterOp.

re: Common gotchas when writing your own p/invoke

Ooh — Fri, 14 Aug 2009 21:52:32 GMT

Full ACK on pinvoke.net - whatever I tried to grab from there didn't work. Been P/Invoking for more than two years without the site and my code happily runs on 32- and 64-bit systems.

@Raymond: Good summary of what you have to pay attention to!

re: Common gotchas when writing your own p/invoke

MadQ — Fri, 14 Aug 2009 20:35:04 GMT

"In Win32, BOOL is a 4-byte type, and BOOLEAN is a 1-byte type."

You might want to add that VARIANT_BOOL is is a 2-byte type where 0 == FALSE and -1 == TRUE.

This is very important when declaring COM interfaces. For interfaces, the CLR marshals System.Boolean as a 2-byte type. A lot of COM interfaces use and mix the Win32 BOOL and VARIANT_BOOL. If the IDL (or the C/C++ header) declares a BOOL, make sure to decorate it with with a MarshalAsAttribute(UnmanagedType.Bool) in your .NET code.

[Excellent points, thanks for contributing. I've linked to your comment from the main article. -Raymond]

re: Common gotchas when writing your own p/invoke

Garthy — Fri, 14 Aug 2009 14:24:53 GMT

On of the Biggest problems I had was interacting with the DDK accross 32/64 bit platforms pack value is 1 for 32bit but for 64bit platforms it's 8

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode, Pack = 1)]

public struct SP_DEVICE_INTERFACE_DETAIL_DATA_W_32

{

public int cbSize;

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 1)]

public string DevicePath;

}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode, Pack = 8)]

public struct SP_DEVICE_INTERFACE_DETAIL_DATA_W_64

{

public int cbSize;

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 1)]

public string DevicePath;

}

This is a simple sturct but it causes problems all over the place

re: Common gotchas when writing your own p/invoke

Joe — Fri, 14 Aug 2009 14:07:46 GMT

Gah. System.Char is not a 'Unicode character' - it is a UTF16LE code unit (and the MSDN documentation could use correcting).

The difference may not seem important at first glance - but I'm sure people who mis-use the Win32 API and think it's OK because it works for them didn't think that understanding the technology they were using was important either.

[See What('s) a character! The article uses the term "character" in its common meaning of "storage character" or "code unit" rather than "linguistic character" or even "code point". -Raymond]

re: Common gotchas when writing your own p/invoke

Miral — Fri, 14 Aug 2009 06:43:47 GMT

I was just about to post what aaron said above; there's a sequential struct alignment missing, I think.

re: Common gotchas when writing your own p/invoke

Mark — Fri, 14 Aug 2009 04:23:56 GMT

By the way, name decoration is of course internal to Microsoft's linker, but DLL imports, COM and RPC are well defined, and they're more the ABI.

re: Common gotchas when writing your own p/invoke

Mark — Fri, 14 Aug 2009 04:01:25 GMT

Karellen: but Win32 was traditionally based in C. MS didn't need a bool type, as it had BOOL standardised. However, various other houses had settled on enum/int/char, which is why C++ tried to fix it.

As for your final question, VC4.2 for one.