Prologue
I have always loathed P/Invoke in an intense manner. I guess it's perhaps due
to the fact that I am a very simple human being and thus I naturally disliked
anything which was not simple. P/Invoke in my opinion was ugly and so
pathetically unnatural. These two facets made it an utterly complicated entity.
Then I came across these beautiful words by Nick Hodapp.
"IJW in C++ is syntactically easier than P/Invoke, and as I said, slightly
more performant." - Nick Hodapp, Microsoft
Two things struck me immediately after I read those words. The first one,
naturally was that there was no word called "performant" in the English
dictionary, though I could actually understand very clearly what Nick Hodapp had
meant by that word. The second more glaring point was that I didn't know what
IJW meant. Later on when I realized that IJW simply meant, "It just works", I
had this feeling for a few seconds that I was stuck in a world of lunacy. But
after I tried it out, I simply said aloud, "It just works". Because, it really
does work. And it's not ugly or unnatural like P/Invoke is. And as Nick Hodapp
said, it's slightly more performant.
Using IJW
All you do is to simply #include
the required C++ header file.
Of course there is always a danger that there will be several name clashes
between the definitions in the header file and the .NET framework classes and
their member functions. I found this out the hard way when I got 100s of
compilation errors. All of them simply said :- "error C2872: 'blahblahblah' :
ambiguous symbol". Now as you can assume, this was a most distressing situation
as far as I was concerned. It took my rather simple brain a couple of minutes to
figure out that, I had to include the header file before all my
using
namespace
directives.
Unlike P/Invoke, where all the data marshalling between .NET types and native
types is done by the compiler, here we must do it ourselves. It's not a
complicated issue at all once you take a look at the
System.Runtime.InteropServices.Marshal
class in the framework.
Jolly nice class I tell ya, with jolly nice functions.
Without further tête-à-tête, let's see some sample code. In the tiny example
program listed below I shall show you how to create a managed class, which can
be instantiated from a managed block, and which uses IJW to call a native API
call. You'll see how much more nicer this looks like when compared to the foul
looking P/Invoke code.
Code Listing
#include "stdafx.h"
#using <mscorlib.dll>
#include <tchar.h>
#include <windows.h>
using namespace System;
using namespace System::Runtime::InteropServices;
public __gc class MsgBox
{
public:
MsgBox(String *str)
{
IntPtr ptrtxt = Marshal::StringToCoTaskMemUni(str);
MessageBoxW(0,(LPCWSTR)ptrtxt.ToPointer(),
L"IJW is cool",0);
Marshal::FreeCoTaskMem(ptrtxt);
}
};
int _tmain(void)
{
String *str;
str = "Nish was here";
MsgBox *m_msgbox = new MsgBox(str);
return 0;
}
I have used StringToCoTaskMemUni
which copies the string to an
unmanaged area in the heap. Once I have made my call, I must free the string
that has been allocated in the unmanaged heap area, because this will not get
garbage collected. Isn't it truly amazing that when IJW existed, a lot of us
were wasting our time with P/Invoke! Of course this is available only for
Managed C++ programmers. The poor C# and VB .NET guys will have to suffer the
P/Invoke monster as that's their only option.
I guess this is one very good reason for the use of Managed C++ ahead of C#.
I am also hoping that this is the first IJW article on CP or perhaps on any
non-Microsoft site. I guess I'll have to wait for Chris M to confirm that. I
also do hope that it has served it's simple purpose. Thank you.
Nish Nishant is a technology enthusiast from Columbus, Ohio. He has over 20 years of software industry experience in various roles including Chief Technology Officer, Senior Solution Architect, Lead Software Architect, Principal Software Engineer, and Engineering/Architecture Team Leader. Nish is a 14-time recipient of the Microsoft Visual C++ MVP Award.
Nish authored C++/CLI in Action for Manning Publications in 2005, and co-authored Extending MFC Applications with the .NET Framework for Addison Wesley in 2003. In addition, he has over 140 published technology articles on CodeProject.com and another 250+ blog articles on his WordPress blog. Nish is experienced in technology leadership, solution architecture, software architecture, cloud development (AWS and Azure), REST services, software engineering best practices, CI/CD, mentoring, and directing all stages of software development.
Nish's Technology Blog :
voidnish.wordpress.com