Hi All,

I have written a wrapper around a C++ class to make it available to C#,
built into a dll. This has gone just fine, but one of the methods in
the C++ class takes a FILETIME pointer as an argument (from windows.h).
For example:

timer.h (C++)
------------
#include "windows.h"

public __gc class foo
{
public:
static void getTime( FILETIME * );
}


However, the problem is when I try to call this from C# (in an unsafe
method). My call to it looks like:

needsTime.cs (C# .NET 2.0)
---------------------
using System.Runtime.InteropServices.ComTypes;

<snip />

FILETIME myTime = new FILETIME();

foo.getTime( &myTime );


Building this produces the following error, which I cannot seem to
resolve:

Argument '1': Cannot convert from
'System.Runtime.InteropServices.ComTypes.FILETIME*' to '_FILETIME*'

Any thoughts?

Thanks in advance!

-Rob

>timer.h (C++)
>------------
>#include "windows.h"
>
>public __gc class foo
>{
> public:
> static void getTime( FILETIME * );
>}
>
>
>However, the problem is when I try to call this from C# (in an unsafe
>method). My call to it looks like:


If you write the wrapper, why not change it to a type more friendly to
managed code? Something like

void getTime(System::Runtime::InteropServices::FILETIME __gc * );


Mattias

--
Mattias Sjögren [C# MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

> If you write the wrapper, why not change it to a type more friendly to
> managed code? Something like
>
> void getTime(System::Runtime::InteropServices::FILETIME __gc * );

Hi Mattias,

That simply moves my dilemna inside the wrapper, which _is_
preferrable, but ultimately I still have to convert from
System::Runtime::InteropServices::FILETIME * to _FILETIME*. (since the
function ultimately being called takes a _FILETIME pointer.)

I still get the same error, though now it is when building the C++ into
a dll.

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Hi All,
>
> I have written a wrapper around a C++ class to make it available to C#,
> built into a dll. This has gone just fine, but one of the methods in
> the C++ class takes a FILETIME pointer as an argument (from windows.h).
> For example:
>
> timer.h (C++)
> ------------
> #include "windows.h"
>
> public __gc class foo
> {
> public:
> static void getTime( FILETIME * );
> }
>
>
> However, the problem is when I try to call this from C# (in an unsafe
> method). My call to it looks like:
>
> needsTime.cs (C# .NET 2.0)
> ---------------------
> using System.Runtime.InteropServices.ComTypes;
>
> <snip />
>
> FILETIME myTime = new FILETIME();
>
> foo.getTime( &myTime );
>
>
> Building this produces the following error, which I cannot seem to
> resolve:
>
> Argument '1': Cannot convert from
> 'System.Runtime.InteropServices.ComTypes.FILETIME*' to '_FILETIME*'
>
> Any thoughts?
>
> Thanks in advance!
>
> -Rob
>



You can't do this without marshaling, Windows.h FILETIME is an unmanaged struct, so the
method is expecting a native struct pointer, you are passing a pointer to a managed type
(value type).
Now, you have to options:
1 you "marshal" the System.Runtime.InteropServices.ComTypes.FILETIME to a long and pass this
as argument, or
2. you declare the C++ method argument in C++ as:
System.Runtime.InteropServices.ComTypes.FILETIME *
and marshall this one to a windows.h FILETIME

Note also that you should get rid of the old ME C++ syntax, use C++/CLI, and fully qualify
the System.Runtime.InteropServices.ComTypes.FILETIME if you don't want to get clashes with
the (deprecated) 'System.Runtime.InteropServices.FILETIME' in V2 of the framework.

Willy.

>That simply moves my dilemna inside the wrapper, which _is_
>preferrable, but ultimately I still have to convert from
>System::Runtime::InteropServices::FILETIME * to _FILETIME*. (since the
>function ultimately being called takes a _FILETIME pointer.)

Right, but it's usually easier to handle it on the C++ side with
type-unsafe casts and memcpys.

In this case, however, since FILETIME is such a trivial struct, I
would simply declare a temporary (Win32) FILETIME variable, fill that
with the values from the managed struct (member by member) and pass it
on to the native code.


Mattias

--
Mattias Sjögren [C# MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

Thanks All,

I have solved it by just declaring a new variable in my wrapper method
of the unmanaged FILETYPE, then pass that to the function that needs
it. The function then populates the values for it, then I immediately
copy the values from the unmanaged FILETIME to the managed FILETIME,
whose address was passed in.

It's a solution ... well, lets call it a workaround.


Thanks again!

-Rob