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Posted 2 May 2002


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Using IJW in Managed C++

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2 May 20023 min read
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


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.


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

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About the Author

Nish Nishant
United States United States
Nish Nishant is a Principal Software Architect based out of Columbus, Ohio. He has over 17 years of software industry experience in various roles including Lead Software Architect, Principal Software Engineer, and Product Manager. Nish was a Microsoft Visual C++ MVP between 2002 and 2015.

Nish is an industry acknowledged expert in the Microsoft technology stack. He authored C++/CLI in Action for Manning Publications in 2005, and had previously co-authored Extending MFC Applications with the .NET Framework for Addison Wesley in 2003. In addition, he has over 140 published technology articles on and another 250+ blog articles on his WordPress blog. Nish is vastly experienced in team management, mentoring teams, and directing all stages of software development.

Contact Nish : If you are interested in hiring Nish as a consultant, you can reach him via his google email id voidnish.

Company Website :

Comments and Discussions

GeneralI'm kind of surprised you think this is simpler.... Pin
TheWerewolf20-Jan-11 11:07
MemberTheWerewolf20-Jan-11 11:07 
QuestionIJW seems not to work with more complicate controls Pin
gunag19-Jul-06 3:48
Membergunag19-Jul-06 3:48 
QuestionHow about resources in the mfc-DLLs Pin
gunag6-Jul-06 3:35
Membergunag6-Jul-06 3:35 
GeneralIJW does not work!!! Pin
SleepingPedant23-Nov-03 19:06
MemberSleepingPedant23-Nov-03 19:06 
General[Message Removed] Pin
immetoz1-Oct-08 9:47
Memberimmetoz1-Oct-08 9:47 
GeneralThat's the smartest interop article... Pin
Stephane Rodriguez.16-Apr-03 11:29
MemberStephane Rodriguez.16-Apr-03 11:29 
GeneralRe: That's the smartest interop article... Pin
Nish Nishant16-Apr-03 16:26
sitebuilderNish Nishant16-Apr-03 16:26 
GeneralRe: That's the smartest interop article... Pin
Stephane Rodriguez.16-Apr-03 18:49
MemberStephane Rodriguez.16-Apr-03 18:49 
GeneralRe: That's the smartest interop article... Pin
Nish Nishant16-Apr-03 18:58
sitebuilderNish Nishant16-Apr-03 18:58 
GeneralRe: That's the smartest interop article... Pin
Tom Archer28-Apr-03 13:28
MemberTom Archer28-Apr-03 13:28 
GeneralRe: That's the smartest interop article... Pin
Nish Nishant28-Apr-03 15:49
sitebuilderNish Nishant28-Apr-03 15:49 
GeneralIJW doesn´t works!!!!!!!!!!!!!!! Pin
tomjackson15-Apr-03 20:08
Membertomjackson15-Apr-03 20:08 
GeneralRe: IJW doesn´t works!!!!!!!!!!!!!!! Pin
Nish Nishant16-Apr-03 16:29
sitebuilderNish Nishant16-Apr-03 16:29 
QuestionHow to resolve names clash? Pin
567890123413-Apr-03 23:08
Member567890123413-Apr-03 23:08 
AnswerRe: How to resolve names clash? Pin
Nish Nishant14-Apr-03 3:25
sitebuilderNish Nishant14-Apr-03 3:25 
GeneralRe: How to resolve names clash? Pin
567890123414-Apr-03 4:05
Member567890123414-Apr-03 4:05 
GeneralRe: How to resolve names clash? Pin
Nish Nishant15-Apr-03 17:38
sitebuilderNish Nishant15-Apr-03 17:38 
GeneralRe: How to resolve names clash? Pin
567890123426-Apr-03 19:27
Member567890123426-Apr-03 19:27 
QuestionNish & Nick!!!??? Pin
15-May-02 19:23
suss15-May-02 19:23 
GeneralPerformant Pin
Nick Hodapp6-May-02 8:52
sitebuilderNick Hodapp6-May-02 8:52 
GeneralRe: Performant Pin
Nish Nishant6-May-02 15:05
sitebuilderNish Nishant6-May-02 15:05 
GeneralRe: Performant Pin
Jamie Hale8-May-02 9:17
MemberJamie Hale8-May-02 9:17 
GeneralRe: Performant Pin
Nish Nishant8-May-02 9:35
sitebuilderNish Nishant8-May-02 9:35 
GeneralRe: Performant Pin
Jamie Hale8-May-02 9:48
MemberJamie Hale8-May-02 9:48 
GeneralRe: Performant Pin
Nish Nishant8-May-02 9:55
sitebuilderNish Nishant8-May-02 9:55 

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