Return value from C++ dll called from C# app

[=?Utf-8?B?Sm9hY2hpbQ==?=]

How would I do, in both ends, to get a return value from a C++ dll called
from C# app?

[=?Utf-8?B?Sm9hY2hpbQ==?=]

More specifically, I would like the return value to be a HRESULT (as it
already is), but I would like to pass a parameter which I can change in the
DLL so that it also has effect in the C# app.

"Joachim" wrote:

How would I do, in both ends, to get a return value from a C++ dll called
from C# app?

[Mattias Sjögren]

>More specifically, I would like the return value to be a HRESULT (as it
already is), but I would like to pass a parameter which I can change in the
DLL so that it also has effect in the C# app.

So something like this?

HRESULT _stdcall MyFunc(int *pi)
{
if (!pi) return E_POINTER;
*pi = 42;
return S_OK;
}

---

[DllImport("your.dll")]
static extern uint MyFunc(ref int pi);

....

int i = 0;
uint hr = MyFunc(ref i);
Mattias

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

[Ben Voigt]

"Mattias Sjögren" <ma********************@mvps.orgwrote in message
news:%2****************@TK2MSFTNGP06.phx.gbl...

>

>>More specifically, I would like the return value to be a HRESULT (as it
already is), but I would like to pass a parameter which I can change in
the
DLL so that it also has effect in the C# app.

So something like this?

HRESULT _stdcall MyFunc(int *pi)
{
if (!pi) return E_POINTER;
*pi = 42;
return S_OK;
}

---

[DllImport("your.dll")]
static extern uint MyFunc(ref int pi);

Works, but bleech, you need untrusted code permission. If you can compile
the C++ code as a managed assembly (C++/CLI), then you would use

public ref class A
{
HRESULT MyFunc(System::Int32% intbyref) { intbyref = 42; return S_OK; }
}

which has almost the identical caller interface, but no need for DllImport
(use a managed reference instead) and needs no special permissions (since
this code will compile with /clr:safe)

...

int i = 0;
uint hr = MyFunc(ref i);
Mattias

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

[Willy Denoyette [MVP]]

"Ben Voigt" <rb*@nospam.nospamwrote in message
news:%2****************@TK2MSFTNGP05.phx.gbl...

>
"Mattias Sjögren" <ma********************@mvps.orgwrote in message
news:%2****************@TK2MSFTNGP06.phx.gbl...

>>

>>>More specifically, I would like the return value to be a HRESULT (as it
already is), but I would like to pass a parameter which I can change in the
DLL so that it also has effect in the C# app.

So something like this?

HRESULT _stdcall MyFunc(int *pi)
{
if (!pi) return E_POINTER;
*pi = 42;
return S_OK;
}

---

[DllImport("your.dll")]
static extern uint MyFunc(ref int pi);

Works, but bleech, you need untrusted code permission. If you can compile the C++ code as
a managed assembly (C++/CLI), then you would use

public ref class A
{
HRESULT MyFunc(System::Int32% intbyref) { intbyref = 42; return S_OK; }
}

which has almost the identical caller interface, but no need for DllImport (use a managed
reference instead) and needs no special permissions (since this code will compile with
/clr:safe)

True, but the OP is talking about existing native C++ code I guess, Mattias is only
illustrating, by example, how you can declare a function that returns an HRESULT and passes
a value by reference.
Note that you can apply the "SuppressUnmanagedCodeSecurityAttribute" to suppress the
security walk when using PInvoke, this achieves the same result as C++/CLI's managed/native
code interop.

Wily.