[C++/CLI]problem with unmanaged C library and callback functions - Managed C++/CLI Discussion Boards

Hey guys,

I have a question that's been plaguing me for a day or so. I'll try to explain as best as possible. No code this time, just some general questions.

I have a hierarchy of Windows forms, MainForm->AdminForm->JobDetailsForm. JobDetailsForm requires objects from MainForm, and AdminForm is just a middle man. Is there a slick way to get information from an object in MainForm to JobDetails form without passing the object through AdminForm? The object is an ArrayList of Objects called Users. I set information in the MainForm, and then I get that information inside of JobDetailsForm. Currently I'm doing something similar to

Pseudo Code:

MainForm
ArrayList users;
...
new AdminForm(users);

AdminForm
...
//no operations on users
new JobDetailsForm(users)

JobDetailsForm
...
//some operations on users

AdminForm has no use for users, it simply displays some information unrelated to users. If possible, I'd also like the operations preformed in JobDetailsForm to be reflected in the users object used in MainForm. I'm thinking a global or static variable could solve this, but from what I understand, there are no global or static variables in managed C++/CLI. Any ideas or suggestions?

[Insert Witty Sig Here]

VonHagNDaz wrote:
I'm thinking a global or static variable could solve this, but from what I understand, there are no global or static variables in managed C++/CLI.

If you choose that route, you can have a ref class with a static constructor and static member methods/properties/fields...How to: Define Static Constructors in a Class or Struct[^]

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Hey Guys,

I'm having a little problem parsing a date and time from a string.

DateTime^ start = gcnew DateTime();

temp = "";
this->thisJob->getStartDate(temp);
start->Parse(temp);

temp is "5/16/2011"

however, after start->parse(temp) the value of start is always "1/1/1 0 Blush | :O

" I'm only interested in the date "5/26/2011". MSDN has several differnt "Parse" methods, and I've tried a few others, but the result is always "1/1/1 0 Blush | :O

"

Sorry for the smileys, I think CP website is taking my returned string I'm typing into the question and converting it into some kind of smiley code.

[Insert Witty Sig Here]

Try something like this...

String ^temp = "5/26/2011";
DateTime start;
if (DateTime::TryParse(temp, start))
{
    // do something with start
}

...or this...

String ^temp = "5/26/2011";
try
{
    DateTime start = DateTime::Parse(temp);

    // do something with start
}
catch (Exception ^)
{
}

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

modified on Monday, May 16, 2011 2:32 PM

That works! I'm a bit confused as to why your code works and mine doesn't. What is the difference between SomeDateTimeObject.Parse, and DateTime::Parse?

[Insert Witty Sig Here]

All the Parse() methods are static (AFAIK) so they return a new DateTime object instead of altering the one you were calling Parse() on.

This would have worked;

start = start->Parse(temp);

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

I see, MSDN wasn't too clear on that. It lead me to believe temp would be modified. Thank you, 5's for both.

[Insert Witty Sig Here]

Hi,
I've got this problem and I don't try to solve it.
I'm using Microsoft Studio 2008 and I want to build a managed application.
This application uses a C unmanaged library.

In particular the library function that I must use is:

error_status TED_PixRad_RegisterEventCallback( eventCallback_t eventCallbackProc,void* customData = NULL ).
(I must use it to hook the event returned by a device).

This function has a callback function parameter with this syntax:

typedef void (*eventCallback_t)( const event_id eventID, const Event *eventData,void* customData );

I' ve found that I must build a wrapper class to use my managed application and the unmanaged library.

I try to build a wrapper class:

file wrapper.h:
#pragma once
#include "stdafx.h"
#include "gcroot.h"

namespace Pixium {

using namespace System;
using namespace System::Runtime::InteropServices;

void cdeclEventCallback(const event_id eventID, const Event *eventData, void* customData );

public ref class Library
{
public:
delegate void eventRegistered(const event_id eventID);

internal:

eventRegistered ^_event_registered;
private:

gcroot<Library^> *_native_handle;
public:
Library();
~Library();
error_status registerEvent(eventRegistered ^evento);
};
}

file wrapper.cpp:
#include "stdafx.h"
#include "wrapper.h"

namespace Pixium {
Library::Library()
{
_native_handle = new gcroot<Library^>();
_event_registered=nullptr;
}
Library::~Library()
{
delete _native_handle;
}
error_status Library::registerEvent(eventRegistered ^evento)
{
_event_registered=evento;
return TED_PixRad_RegisterEventCallback(cdeclEventCallback,_native_handle);
}

void cdeclEventCallback(const event_id eventID, const Event *eventData, void* customData )
{
gcroot<Library^> & native_handle = *((gcroot<Library^>*)customData);
native_handle->_event_registered(eventID);
}
}

In an application class I try to use this wrapper to receive the values event returned.

In particular in the constructor I initialize the wrapper object:
Form1(void)
{
InitializeComponent();
this->lib=gcnew Library(); //istanzio il wrapper
//event_registered= gcnew Library::eventRegistered(this,&Form1::processEvent);
this->registerEvent();
}
and in the function I call a wrapper event register funciotn:

void Form1::registerEvent()
{
//error_status err_reg_event=TED_PixRad_RegisterEventCallback((eventCallback_t)Marshal::GetFunctionPointerForDelegate(del).ToPointer(),_native_handle);
error_status err_reg_event=this->lib->registerEvent(); //utilizzo il wrapper
if (this->TestError(err_reg_event)){
this->button2->Visible=true;
}
}

The problem: I think a mistake to use the wrapper by my application or also in wrapper building.
Infact I' ve got error on the callback function when I try to receive event message.

I apologize for my bad English, hoping to be able to explain problem

Someone can indicates me an example or tutorial to learn how can I work with managed C++/CLI and unmanaged C type?
Thanks

I think the MSDN topic: How to: Marshal Callbacks and Delegates Using C++ Interop addresses what you need to do.

I think the key will be placing the #pragma managed/unmanaged and using Marshal::GetFunctionPointerForDelegate

John

Hi John,
thanks to help me.
I followed your advice and I've read How to: "Marshal Callbacks and Delegates Using C++ Interop"
I've tried to work on my application.
I' ve done this:

1) I decided to create a simple example without wrapper.h. So I' working only in a Form1.h.
2) Since my form1.exe work with the library of an electronic device and I constantly receive
the events returned by this device, I thinked to put the define of delegate, IntPtr and the callback unmanaged function as form1 private attributes and I declared them in the Form1 constructor:

Form1(void)
{
InitializeComponent();
_native_handle=new gcroot<Form1^>();
evento=gcnew eventRegistered(cdeclEventCallback);
gch =GCHandle::Alloc(evento);
ip=Marshal::GetFunctionPointerForDelegate(evento);
cb=static_cast<eventCallback_t>(ip.ToPointer());
GC::Collect();
this->registerEvent();

}

3) After, in constructor, I call the function registerEvent(). In this function I put the calling at the library function "TED_PixRad_RegisterEventCallback":

void Form1::registerEvent()
{
error_status er_return=TED_PixRad_RegisterEventCallback(cb,_native_handle);
if (this->TestError(er_return)){
this->button2->Visible=true;
}

}

4) the callback implementation in my Form1 is this:
void cdeclEventCallback(const event_id eventID, const Event *eventData, void* customData )
{
gcroot<Form1^> & native_handle = *((gcroot<Form1^>*)customData);
native_handle->processEvent(eventID,"evento");
}

Oss1: I think I must using _native_handle and not passing this (Form1 refer).
Oss3: processEvent is an internal function of Form1 that receive the code eventID and write the code mean in a form1 label.
Oss2: The compilation is without errors or warnings.

Assuming that I can not debug because the device connected to a machine other than the development,I have seen that the device gives me error event handling return
In particular, writing message on Form1 labels I' ve seen that I cannot enter in cdeclEventCallback function and I cannot call processEvent().

I can not understand what could be in error and this is a logic error in using Marshal:: GetFunctionPointerForDelegate in my example.

Have you got any advice for me?

Thanks for the help

OSS1:
I find that probably the error lies in the way the gcroot, because if I pass NULL in place of _native_handle and put processEvent () outside of Form1, I do not come back errors on callback events in the logs of the device;

OSS2: I used gcroot to pass ref of FORM1 between the managed and unmanaged code;

OSS3: I remember that the prototype of "TED_PixRad_RegisterEventCallback" library function is:

error_status TED_PixRad_RegisterEventCallback( eventCallback_t eventCallbackProc,
void* customData = NULL )

and the protorype of callback function by unmanaged library to my managed applicaiton is:

typedef void (*eventCallback_t)( const event_id eventID, const Event *eventData,
void* customData );

and customData for me is my Form1 (in general my object class).

PROBLEM:
I must implements processEvent like object function (then as Form1 funciotn) and so I must to pass FORM1 refer in TED_PixRad_RegisteredEventCallback that is the function of unmanaged library.
Any ideas?

I've never done this with C++/CLI but I've done it quire frequently between C# (managed) and C (native), and the one thing to remember is in the native world you must declare the callback function as StdCall.

You can read some about C#-C in this article of mine[^].

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

Hi luc,
thantks for advice.
Reading your article, I had an idea:
- I haven't used gcroot but directly GCHandle.
- I must casting because parameter library function is void*.

This is what I've done:
1) I 've used GCHandle to build an handle to object (for my example FORM1) and I've used GCHandle.Alloc() to reserve memory when i send object refer from managed code to unmanaged library. I' ve done this in the constructor. So it is:

Form1(void)
{
    InitializeComponent();
    evento=gcnew eventRegistered(Form1::cdeclEventCallback);
    gch =GCHandle::Alloc(evento);
    ip=Marshal::GetFunctionPointerForDelegate(evento);
    cb=static_cast<eventCallback_t>(ip.ToPointer());
    GC::Collect();
    gch3=GCHandle::Alloc(this);  //<-**************
    this->registerEvent();
}

2) I've used GCHandle::ToIntPtr to obtain pointer of handle to send like parameter.I've done this in my registerEvent() function when i call library funciton. registerEvent() now is:

void Form1::registerEvent()
{
    error_status er_return=TED_PixRad_RegisterEventCallback(cb,(void*)(GCHandle::ToIntPtr(gch3)));  //<******

    if (this->TestError(er_return)){
        this->button2->Visible=true;
    }
}

3) Since library function receives void* customData parameter and it returns this in callback function, I must cast my pointer Form1 refer from IntPtr to void*. After, in the callback function I must casting from void* to IntPtr and in second time I must casting from intPtr to Form1^.
The implementation of the callback funciton now is:

static void Form1::cdeclEventCallback(const event_id eventID, const Event *eventData, void* customData )
{
    GCHandle gch4 = GCHandle::FromIntPtr((IntPtr)(customData)); //<-***************
    Form1^ frm = (Form1^)gch4.Target;                           //<-***************
    frm->label3->Text="GESTIONE EVENTO";
    frm->label3->Refresh();
    frm->processEvent(eventID,"");                           //<-***************

}

Now I must call processEvent like an object function and not like Form1 external function.
---------------------------------------------------------------

I compiled without problems and doing some tests I've seen that behavior is correct, that the occurrence of an event correctly calls the callback function and that this uses the correctly reference at Form1.
Less than denials I think the problem is solved, thank you all for your help.

Smile | :)

I'm not sure I understand everything you're doing here, however I'm glad you got it working.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

Hello,

I'm a long time lurker on CodeProject, and finally have a problem that I'm getting nowhere on.

We have a C++ application we're building in VS2008 that uses "it just works" interop to create reports using Crystal Reports. So there is a C# ReportHandler (which contains a reference to the Report itself), and a C++/CLI ReportWrapper. If the ReportWrapper is built as a static lib, it works under both WinXP x32 and Win7 x64. However, when the ReportWrapper is built as a DLL, it works under WinXP x32 but crashes under Win7 x64 (it's built as a x86 application either way).

It crashes not when the app starts, but when you try to bring up the File:Open dialog using CFileDialog::DoModal(). The call stack is not obvious:

ntdll.dll!77158eb9() 	<br />
[Frames below may be incorrect and/or missing, no symbols loaded for ntdll.dll]	<br />
AcXtrnal.dll!60af9480() 	<br />
KernelBase.dll!76b54958() 	<br />
comdlg32.dll!769ee4ab() 	<br />
comdlg32.dll!769eea8b() 	<br />
comdlg32.dll!769cfa0e() 	<br />
comdlg32.dll!769b8a57() 	<br />
comdlg32.dll!769b876c() 	<br />
shell32.dll!750861ee() 	<br />
shell32.dll!75086159() 	<br />
ole32.dll!74dd09bf() 	<br />
shlwapi.dll!75d4b6cf() 	<br />
ntdll.dll!7718808e() 	<br />
ntdll.dll!77159fc5()

Here are the last few lines of the debug output window.

088c:0e48 @ 159626312 - LdrpRunInitializeRoutines - INFO: Calling init routine 64E71291 for DLL "C:\Windows\system32\NetworkExplorer.dll"<br />
088c:0e48 @ 159626312 - LdrpLoadDll - RETURN: Status: 0x00000000<br />
088c:0e48 @ 159626312 - LdrLoadDll - RETURN: Status: 0x00000000<br />
088c:0e48 @ 159626312 - LdrGetProcedureAddressEx - INFO: Locating procedure "DllGetClassObject" by name<br />
088c:0e48 @ 159626312 - LdrGetProcedureAddressEx - INFO: Locating procedure "DllCanUnloadNow" by name<br />
088c:0e48 @ 159626328 - LdrGetProcedureAddressEx - INFO: Locating procedure "PropVariantToUInt64" by name<br />
088c:0e48 @ 159626328 - LdrGetProcedureAddressEx - INFO: Locating procedure "PropVariantToInt32" by name<br />
088c:0e48 @ 159626328 - LdrGetProcedureAddressEx - INFO: Locating procedure "PropVariantToInt32WithDefault" by name<br />
088c:0e90 @ 159626328 - LdrGetProcedureAddressEx - INFO: Locating procedure "OpenThreadToken" by name<br />
First-chance exception at 0x77158eb9 in theapp.exe: 0xC0000005: Access violation writing location 0x00000014.<br />
088c:0e90 @ 159626328 - LdrGetProcedureAddressEx - INFO: Locating procedure "OpenProcessToken" by name<br />
Unhandled exception at 0x77158eb9 in theapp.exe: 0xC0000005: Access violation writing location 0x00000014.

If I force the "bVistaStyle" flag in CFileDialog to false, the dialog does work without crashing the app; however, it then causes strange out of memory errors later on when we try to actually load a file (using dynazip). That tells me that something nefarious is going on, other than just with the CFileDialog (I suspect some strange DLL corruption).

Other oddities:
- we have a similar Report/ReportHandler/ReportWrapper in a different application, and there are no problems with that app.
- if the app is built in release configuration under WinXP x86, it runs fine when installed on Win7 x64.
- if the app is built in release configuration under Win7 x64 (as an x86 project), it runs fine.

So it only crashes when running the debug build (whether debugging or not).

Here's what I've tried so far:
- I compared project settings between the app that works and the one that doesn't. As far as I can tell they're the same.
- I compared project settings between the Release and Debug configurations.
- I created a dummy test MFC app and started pulling in libraries/assemblies/dlls from the app that doesn't work; in the test app, however, the same Report/ReportHandler/ReportWrapper works properly. However, I have not pulled in all of the libraries that are linked into the app.
- I've reread about implementing IJW interop (someone else implemented it) to confirm we've set it up properly.
- I've tried depends (x86), but depends crashes when I try to profile the app.
- I've enabled loader snaps to try and see if anything odd is going on, but have limited experience looking at DLL loading.
- various and sundry other things that I can't think of right now, all to no avail (I've been struggling with this for a while).

Any suggestions on how to approach this problem would be most welcome. Given what's going on, I think there's actually a deeper problem underlying this that's only exposed in this particular configuration (when built as a DLL) -- I don't think it's just a matter of the DLL configuration being the problem.

Gosh, on the surface I can only hazard a guess. You seem to have covered things pretty thoroughly though.

Some wild-assed guesses:

1. When you statically link and run the app, the .NET framework is automatically loaded. When you dynamically link and run, perhaps a different version of the framework is started outside of your control. For example, if there's a shell extension pulled in by the Open dialog, perhaps it's loading .NET 2 and you need 3.5 or 4? This could throw an exception when your DLL finally gets loaded.

2. Does the DLL form reference a C# assembly and fail b/c you need to handle the AppDomain.AssemblyResolve event? Just having the assembly in the same dir as the C++/CLI DLL does NOT mean that C# assembly will be found automatically as I've learned the hard way.

3. Any clues in the Fusion Log views after the failed load? (use fuslogvw.exe) or in the System Event viewer logs?

I'll ponder more but it's hard to help w/o playing around w/ things as I'm sure you're aware...

John

Thanks, John, I appreciate the effort. I don't mind guesses at this point, wild-assed or not.

1. I'll look further into that to make sure we're binding to the correct version. We've typically deployed our app binding to .NET 2, to keep the installer footprint small. Unfortunately I can't use depends to find out exactly what's being loaded.

2. I have "resolve #using References" set to the output folder where the assembly DLL is built, and I've made the assembly a dependency of the wrapper library in the VS solution. I've set references for it in no other way.

3. No clues. I ran fuslogvw and enabled all logging; when I run the app to point of failure, nothing appears in the log so I presume that means no binding is triggered. In my test app that does work, nothing shows up in the Fusion log until I actually launch the report. The app that's failing never even gets that far (I just run it and do File:Open).

Trevor

How about running the app under Application Verifier. This has helped me find some pretty subtle issues with our hybrid C++, C++/CLI, C# app.

It will hang for me if I setup App Verifier and debug as a Mixed mode app. It does work if you change the project debug settings to debug as Native Only.

If it is a pointer bug as jschell mentions this could help nail it early.

John

Thanks for all the input, everyone. I'm currently trying out AppVerifier, something I wasn't previously aware of. It helped me figure out that there's a buried call to LoadLibrary() within a DllMain() and I'm just testing now to see if that's our issue.

Pointer bug.

A system exception is caused with the OS detects the app trying to do something that it shouldn't.

The execution environment impacts how a pointer bug impacts an application.
Thus in one place it might work without problem. In another it fails.

The crash can occur long after the actual place where the bug exists.

Presuming the only unmanaged code is via interop the most likely explanation is that it the API is being used incorrectly. Parameter sizing would seem to be likely possibility.

Could also be a bug in one of the libraries you are using.

That was it! We had a DLL unrelated to C++/CLI that was triggering a buried LoadLibrary() within its DllMain. Once removed, it's running fine. Talk about a red herring: it had nothing to do with C++/CLI, it just happened that by linking in that project, it pushed the app over the edge (but only in Debug and only in Win7). Nasty. It's a problem that's been plaguing us for months (but we were able to avoid it up until recently).

Thanks John for suggesting Application Verifier. Of course it didn't say "hey, this is wrong", but it did raise a flag in the DLL that was causing all the trouble and got me to focus on what was going on there. And that's exactly what I was looking for: not necessarily "tell me what's wrong with my code" but "how do I figure out what's wrong" and your suggestion helped nail it. And jschell, you were right about it being a bug in a different library whereas I had focused mainly on the C++/CLI project itself.

So thanks both to John Schroedl and to jschell for taking the time to respond, and to CodeProject for the great site. Much appreciated!

Trevor

Hi guys, I'm having a small problem, and I'd like to know what you guys think.

User.h:

void User::getJobs(ArrayList^ jobs)
{
	jobs = this->jobs;
}

UserForm.h:

UserForm(User^ currentUser)
		{
			InitializeComponent();
			//
			//TODO: Add the constructor code here
			//
			this->user = gcnew User();
			this->allJobs = gcnew ArrayList();

			Job^ currentJob = gcnew Job();
			ListViewItem^ item = gcnew ListViewItem();

			this->user = *currentUser;

			this->user->getJobs(this->allJobs);


			for(int i = 0; i < allJobs->Count; i++)
			{
				currentJob = (Job^)allJobs[i];

				String^ temp = "";
				currentJob->getCustomerName(temp);
				item->SubItems->Add(temp);

				temp = "";
				currentJob->getProjectName(temp);
				item->SubItems->Add(temp);

				Job::EN_PRIORITY^ priority = Job::EN_PRIORITY::EN_PRIORITY_0;
				currentJob->getPriority(priority);
				switch(*priority)
				{
				case Job::EN_PRIORITY::EN_PRIORITY_0:
					item->SubItems->Add("NONE");
					break;
				case Job::EN_PRIORITY::EN_PRIORITY_1:
					item->SubItems->Add("1");
					break;
				case Job::EN_PRIORITY::EN_PRIORITY_2:
					item->SubItems->Add("2");
					break;
				case Job::EN_PRIORITY::EN_PRIORITY_3:
					item->SubItems->Add("3");
					break;
				case Job::EN_PRIORITY::EN_PRIORITY_4:
					item->SubItems->Add("4");
					break;
				case Job::EN_PRIORITY::EN_PRIORITY_5:
					item->SubItems->Add("5");
					break;
				default:
					item->SubItems->Add("NONE");
					break;
				}
				listViewAllJobs->Items->Add(item);

				//add time stuff once I figure it out
			}
		}

I can see that when getJobs() completes job in Job.h equals the values I'm trying to retrieve, but once the function returns, this->allJobs is blank. Any ideas?

[Insert Witty Sig Here]

modified on Friday, May 13, 2011 8:54 AM

If you are expecting getJobs() to change the incoming 'jobs' parameter to reference a different ArrayList even after the function returns, you'll need to use a "tracking reference".

To do that use the % decoration and declare the function like this:

void User::getJobs(ArrayList^% jobs)
{
	jobs = this->jobs;
}

An alternative would be to loop and copy all the items from this->jobs into jobs.

John

That did the trick! I'm new to managed code and c++/CLI. All of these new operators are throwing me for a loop. Darn Windows forms projects!

[Insert Witty Sig Here]

I am animating a ball and I need something faster then what I'm getting with the form Timer() control.

Is there anything faster that I can use to speed up the animation?

Thanks.