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Using IJW in Managed C++

, 2 May 2002
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A basic introduction to using IJW instead of P/Invoke in Managed C++. This is also the first CP article on IJW.


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
    MsgBox(String *str)
        IntPtr ptrtxt = Marshal::StringToCoTaskMemUni(str);
            L"IJW is cool",0);

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.


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About the Author

Nish Nishant

United States United States
Nish is a real nice guy who has been writing code since 1990 when he first got his hands on an 8088 with 640 KB RAM. Originally from sunny Trivandrum in India, he has been living in various places over the past few years and often thinks it’s time he settled down somewhere.
Nish has been a Microsoft Visual C++ MVP since October, 2002 - awfully nice of Microsoft, he thinks. He maintains an MVP tips and tricks web site - where you can find a consolidated list of his articles, writings and ideas on VC++, MFC, .NET and C++/CLI. Oh, and you might want to check out his blog on C++/CLI, MFC, .NET and a lot of other stuff -
Nish loves reading Science Fiction, P G Wodehouse and Agatha Christie, and also fancies himself to be a decent writer of sorts. He has authored a romantic comedy Summer Love and Some more Cricket as well as a programming book – Extending MFC applications with the .NET Framework.
Nish's latest book C++/CLI in Action published by Manning Publications is now available for purchase. You can read more about the book on his blog.
Despite his wife's attempts to get him into cooking, his best effort so far has been a badly done omelette. Some day, he hopes to be a good cook, and to cook a tasty dinner for his wife.

Comments and Discussions

GeneralRe: That's the smartest interop article... PineditorNishant S28-Apr-03 16:49 
GeneralIJW doesn´t works!!!!!!!!!!!!!!! Pinmembertomjackson15-Apr-03 21:08 
GeneralRe: IJW doesn´t works!!!!!!!!!!!!!!! PineditorNishant S16-Apr-03 17:29 
QuestionHow to resolve names clash? PinmemberAlex Farber14-Apr-03 0:08 
AnswerRe: How to resolve names clash? PineditorNishant S14-Apr-03 4:25 
GeneralRe: How to resolve names clash? PinmemberAlex Farber14-Apr-03 5:05 
GeneralRe: How to resolve names clash? PineditorNishant S15-Apr-03 18:38 
GeneralRe: How to resolve names clash? PinmemberAlex Farber26-Apr-03 20:27 
QuestionNish & Nick!!!??? PinmemberOneAngryProgrammer15-May-02 20:23 
GeneralPerformant PinsitebuilderNick Hodapp (MSFT)6-May-02 9:52 
GeneralRe: Performant PinmemberNish [BusterBoy]6-May-02 16:05 
GeneralRe: Performant PinmemberJamie Hale8-May-02 10:17 
GeneralRe: Performant PinmemberNish [BusterBoy]8-May-02 10:35 
GeneralRe: Performant PinmemberJamie Hale8-May-02 10:48 
GeneralRe: Performant PinmemberNish [BusterBoy]8-May-02 10:55 
GeneralRe: Performant PinmemberJamie Hale8-May-02 11:07 
GeneralRe: Performant PinmemberNish [BusterBoy]8-May-02 11:15 
GeneralRe: Performant PinmemberBruno3-Oct-03 3:41 
GeneralRe: Performant PinmemberThomas Freudenberg8-May-02 11:04 
GeneralRe: Performant PinmemberNish [BusterBoy]8-May-02 11:07 
GeneralRe: Performant PinmemberThomas Freudenberg8-May-02 11:15 
GeneralRe: Performant PinmemberNish [BusterBoy]8-May-02 11:19 
GeneralRe: Performant PinmemberThomas Freudenberg8-May-02 11:24 
GeneralRe: Performant PinmemberNish [BusterBoy]8-May-02 11:28 
GeneralRe: Performant PinmemberThomas Freudenberg8-May-02 11:29 
GeneralRe: Performant PinmemberNish [BusterBoy]8-May-02 11:32 
GeneralRe: Performant PinmemberJamie Hale8-May-02 11:11 
GeneralRe: Performant PinmemberNish [BusterBoy]8-May-02 11:17 
GeneralGood job Nish PinmemberShog93-May-02 21:33 
GeneralRe: Good job Nish PinmemberNish [BusterBoy]3-May-02 21:38 
GeneralRe: Good job Nish PinmemberLee Alexander4-May-02 1:49 
GeneralRe: Good job Nish PinmemberNish [BusterBoy]4-May-02 7:00 
QuestionThis is the first one, right? PinmemberNish [BusterBoy]3-May-02 8:29 

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