c# to C++ - transfer an array of int*

Posted on 2004-10-12
Last Modified: 2008-01-09
So I was in a hurry the other day and couldn't figure out the *right* way to do something.  Instead I ended up with this lovely funtion in my .cpp library:

int HoldEmLibrary::CompareSixHands(Deck handA,                                                   Deck handB,
                    Deck handC,
                    Deck handD,
                    Deck handE,
                    Deck board,
                   int *retCount,
                   int *retHandACount,
                   int *retHandBCount,
                   int *retHandCCount,
                   int *retHandDCount,
                   int *retHandECount,
                   int *retTieCount,
                   int *HandsA0,
                   int *HandsA1,
                   int *HandsA2,
                   int *HandsA3,
                   int *HandsA4,
                   int *HandsA5,
                   int *HandsA6,
                   int *HandsA7,
                   int *HandsA8,
                   int *HandsB0,
                   int *HandsB1,
                   int *HandsB2,
                   int *HandsB3,
                   int *HandsB4,
                   int *HandsB5,
                   int *HandsB6,
                   int *HandsB7,
                   int *HandsB8,
                   int *HandsC0,
                   int *HandsC1,
                  int *HandsC2,
                  int *HandsC3,
                  int *HandsC4,
                  int *HandsC5,
                  int *HandsC6,
                  int *HandsC7,
                  int *HandsC8,
                  int *HandsD0,
                  int *HandsD1,
                  int *HandsD2,
                  int *HandsD3,
                  int *HandsD4,
                  int *HandsD5,
                  int *HandsD6,
                  int *HandsD7,
                  int *HandsD8,
                  int *HandsE0,
                  int *HandsE1,
                  int *HandsE2,
                  int *HandsE3,
                  int *HandsE4,
                  int *HandsE5,
                  int *HandsE6,
                  int *HandsE7,
                  int *HandsE8

Which is called like this from an unsafe funtion in C#:

                  int* iHandsA = stackalloc int[9];
                  int* iHandsB = stackalloc int[9];

                  for (int icnt = 0; icnt <9; icnt++)
                        iHandsA[icnt] = 0;
                        iHandsB[icnt] = 0;

                  int iCount = lib.CompareTwoHands(d1,d2,d3,&iCnt,&iH1,&iH2,&iTie,


Obviously this is fugly and leads to ugliness on both ends...but for the life of me, I couldn't figure out the right way to do it.  Help?


Question by:mittelhauser
  • 6
  • 4

Author Comment

ID: 12290574
I presume it is obvious but what I would prefer is to pass the various int* as arrays instead of indvidually.  
LVL 14

Accepted Solution

AvonWyss earned 500 total points
ID: 12290796
Well, just pass them as arrays! The marshaller does support this, just use the MarshalAs-Attribute to specify what it is:

[DllImport ("SomeDll.dll")]
public static extern void ExternalMethodWithConstantSizedArray([MarshalAs(UnmanagedType.LPArray, SizeConst=3)] Vertex[] data);


[DllImport ("SomeDll.dll")]
public static extern void ExternalMethodWithVaribaleSizedArray([MarshalAs(UnmanagedType.LPArray, SizeParamIndex=1)] Vertex[] data, long size);

That should do the trick...
LVL 14

Expert Comment

ID: 12290821
Note that if you want to retrieve data from the external method, you can use the ref or out modifier and the In- and Out-Attributes. The marshaller then also copies data back from unmanaged space to managed space.
Master Your Team's Linux and Cloud Stack!

The average business loses $13.5M per year to ineffective training (per 1,000 employees). Keep ahead of the competition and combine in-person quality with online cost and flexibility by training with Linux Academy.


Author Comment

ID: 12291146
I guess I need a more specific answer because I can't figure out how to apply that.

It has been awhile since I messed around with c++ but I needed to for this app.  Some more specifics, the C++ function is in managed code.  I need the C++ function to fill-in all of the ints which are passed.

Can you provide me an example declaration for both the C++ function and the C# call.  Just take a case where I want to pass some parameters (say 2 strings for the example) to a C++ function which uses those parameters to calculate 20 int values,  I need to get those 20 integers back to the C# function that called.  My current solution has the C# pass 20 int* but that is ugly and requires unsafe code...

LVL 14

Expert Comment

ID: 12291358
Have a look at this USENET discussion:

I believe that this is what you are looking for.

Author Comment

ID: 12291675
Well maybe but it doesn't seem like the solution given in the post actually works.  I get the following:

c:\code\poker\HoldEmLib\HoldEmLib.h(105): error C3162: 'int __gc *__gc * ' : __gc pointers to interior __gc pointers cannot be declared

when I try to declare a test function in the C++ lib:

void HoldEmLibrary::TestArrayPass(int __gc * __gc * pArray) like the example.

I just feel like I am making this too hard.  All I want to do is have a managed C++ function return a set of ints to a managed C# app...seems like a common thing to do...right?

LVL 14

Expert Comment

ID: 12291721
Er, why are you doing "int __gc * __gc * pArray"? You only need one __gc * - the one that points to the start of the array, right? And this you can then use as ref or out (when you apply the OutAttribute on the C++ code) in the C# part.
LVL 14

Expert Comment

ID: 12291758
Here's the MSDN reference to the different __gc usages:

I'm sorry that I can't provide you with a working example, but I don't use C++ and have just been importing exported dll functions using the .NET marshaller so far, thus my first comment since I didn't realize you were talking of managed C++.

Author Comment

ID: 12292155
Well I solved the problem by moving the C++ functions I needed into an unmanaged DLL and using the orginal suggestion.  Not really a true solution but it worked for me...I'll award you the points.
LVL 14

Expert Comment

ID: 12292174
Thank you. As I said, I'm sorry, but I haven't used managed C++, so I don't really have a clue about your specific question with managed C++. But I'm glad it worked with unmanaged code.

Featured Post

Windows Server 2016: All you need to know

Learn about Hyper-V features that increase functionality and usability of Microsoft Windows Server 2016. Also, throughout this eBook, you’ll find some basic PowerShell examples that will help you leverage the scripts in your environments!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
WCF Service Application cannot connect from TCP terminal 1 32
Media.Imaging 1 18
Graphics 2 28
InputLanguage 1 26
Article by: Ivo
C# And Nullable Types Since 2.0 C# has Nullable(T) Generic Structure. The idea behind is to allow value type objects to have null values just like reference types have. This concerns scenarios where not all data sources have values (like a databa…
Introduction This article series is supposed to shed some light on the use of IDisposable and objects that inherit from it. In essence, a more apt title for this article would be: using (IDisposable) {}. I’m just not sure how many people would ge…
This Micro Tutorial hows how you can integrate  Mac OSX to a Windows Active Directory Domain. Apple has made it easy to allow users to bind their macs to a windows domain with relative ease. The following video show how to bind OSX Mavericks to …
Email security requires an ever evolving service that stays up to date with counter-evolving threats. The Email Laundry perform Research and Development to ensure their email security service evolves faster than cyber criminals. We apply our Threat…

778 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question