_com_error not caught by 'Try-Catch' code - C / C++ / MFC Discussion Boards

Re: volatile local variable

econy6-Nov-13 4:44

econy

6-Nov-13 4:44

thanks, what you said like:

C++

volatile int* aPtr = aSharedMem;

right? then in another thread,

C++

aSharedMem = aNewValue;

then in the current thread, stalled before aSharedMem=aNewValue, then resume, *aPtr get the aNewValue.

if local variable just copy a global's value, like:
volatile int aLocal = aGlobal;
then in another thread, aGlobal = aNewValue;
in current thread, stalled before aGlobal = aNewValue, then resume, aLocal will get aNewValue?

Re: volatile local variable

pasztorpisti6-Nov-13 5:15

pasztorpisti

6-Nov-13 5:15

C++

// global scope. some other threads may use this pointer after its initialization...
int* globalptr;

void myfunc()
{
    volatile int localvar = 0;
    globalptr = &localvar;
    //blah blah
    //wait for something
    
    // start using the volatile var again:
    printf("localvar: %d\n", localvar);
    // In this case the compiler is forced to read up the value of
    // localvar again from memory even if it would be present in a register.
    // Maybe the compiler is smart enough to figure out that forming a pointer
    // to the local var is suspicious but even if you hide this from the compiler
    // with some ugly magic it will read the value from the memory when it comes
    // to printing/using it without doing any optimizations/caching.
}

Re: volatile local variable

econy6-Nov-13 5:36

econy

6-Nov-13 5:36

is the following scenario, the volatile is useful?

C++

//global scope
int globalVar;

//in task1
void task1SetGlobal(void)
{
  
  if (xyz == 100) 
     globalPtr = 100;
}

...
//in task2
void task2GetGlobal(void)
{
  volatile int localVar = 0;

  localVar = globalVar;

  if (localVar < 100 ) doSth;
  else if (localVar == 100) do100Thing;

}

Re: volatile local variable

pasztorpisti6-Nov-13 5:39

pasztorpisti

6-Nov-13 5:39

Not really. In order to understand volatile you should first understand some other concepts like multithreading and caching and all the related problems that can cause problems along with the optimizations done by the compiler.

Re: volatile local variable

Aescleal6-Nov-13 4:49

Aescleal

6-Nov-13 4:49

It's not necessarily bad design to pass a reference to a local variable to another thread for processing. One example of where it might come in handy is splitting up an array into chunks and processing each chunk in separate threads. However using volatile as a synchronisation mechanism is not the sort of thing I'd recommend to try and avoid a proper synchronisation mechanism (i.e. a condition variable).

Re: volatile local variable

pasztorpisti6-Nov-13 5:09

pasztorpisti

6-Nov-13 5:09

Then we agree, in this case some kind of memory fence is used for synchronization that is usually built into the synch primitives like events. In this case you usually make a function call too to pass the job to another thread and usually this already prevents a compiler from optimizing away some things.

Re: volatile local variable

jschell6-Nov-13 8:03

jschell

6-Nov-13 8:03

Probably just me but given the code that was posted I can't see any reason for volatile.

_com_error not caught by 'Try-Catch' code

Mike Grove5-Nov-13 22:14

Mike Grove

5-Nov-13 22:14

I have added some code (to an existing MFC/ATL application), to communicate with a piece of hardware that comes complete with com-based driver software.

(Before I forget: I'm writing C++ in Visual Studio 2010, for Windows7).

My code is based closely upon the sample code that the hardware manufacturer supplied, and is as follows;

C++

#import "GlobMgr.dll"	no_namespace // I/O funtionality
#import "IviDriverTypeLib.dll"	no_namespace // IVI inherent functionality
#import "agu265x.dll"	no_namespace // Instrument specific functionality

IAgilentU265xPtr spAgDrvrSlot1;

CCMDS::CCMDS( ...class details not relevant... )
  : CUSBDevice( ...ditto... )
{
  // Must first call either CoInitialize or CoInitializeEx to initialize COM **DON'T NEED THIS BIT - COM ALREADY INITIALISED**
  //HRESULT hr = S_OK;
  //hr = CoInitialize( NULL );
  //if ( hr != S_OK )
  //{
  //	if ( hr == S_FALSE )
  //	{
  //		AfxMessageBox( "Com Already Initialised" );
  //	}
  //	else
  //	{
  //		AfxMessageBox( "Co-initialise Failed" );
  //	}
  //}

  // Create and Initialise instances of the Agilent driver for
  // each of the four U2635A I/O modules in the U2781A rack
  spAgDrvrSlot1.CreateInstance( __uuidof( AgilentU265x ) );

  try
  {
	spAgDrvrSlot1->Initialize( "USBInstrument1", VARIANT_FALSE, VARIANT_TRUE, "" );
  }
  catch ( _com_error e )
  {
	AfxMessageBox( "Driver Initialise Failed" );
  }

HOWEVER, my code crashes at the Initialize(USBInstrument1...) statement with a Windows dialog saying

Quote:
First-chance exception at 0x755bb9bc in IOHandler.exe: Microsoft C++ exception: _com_error at memory location 0x001de4e0..

Why this code fails at all is a mystery but the big question is why does Windows crash with a dialog rather than my Try-Catch code catching the error in the controlled fashion I'd hoped for??

Re: _com_error not caught by 'Try-Catch' code

Richard MacCutchan5-Nov-13 22:26

Richard MacCutchan

5-Nov-13 22:26

Presumably something in Windows is catching the error and not re-throwing it. You may wish to talk to the people who provided this code for more help.

Veni, vidi, abiit domum

Re: _com_error not caught by 'Try-Catch' code

Mike Grove5-Nov-13 22:53

Mike Grove

5-Nov-13 22:53

Ok, got it thanks - Windows was catching the error and not re-throwing it because... I'm running in Debug and had Visual Studio set to catch all Exceptions Blush | :O

Re: _com_error not caught by 'Try-Catch' code

Aescleal5-Nov-13 22:36

Aescleal

5-Nov-13 22:36

Something you might have missed: You can set the VC++ debugger up to catch exceptions where they're thrown and it generates a message like the dialogue you're getting. Are you running under the debugger with that setting enabled?

If you're not running under a debugger then it's something else but I thought I'd try and clear that up first!

Re: _com_error not caught by 'Try-Catch' code

Mike Grove5-Nov-13 22:57

Mike Grove

5-Nov-13 22:57

Ooops, sorry - I missed your reply earlier! Yes, you were correct - thank-you Thumbs Up | :thumbsup:

Feeling like a newbie (again) Frown | :(

Re: _com_error not caught by 'Try-Catch' code

Aescleal5-Nov-13 23:38

Aescleal

5-Nov-13 23:38

No probs - I only thought about it as I had the same problem last week Smile | :)

mfc

shizhanbiao5-Nov-13 19:59

shizhanbiao

5-Nov-13 19:59

<pre>Dialog box with two buttons, when I drag and drop to another button area swap places. How to do it.
</pre>

Re: mfc

CPallini5-Nov-13 21:32

CPallini

5-Nov-13 21:32

Coding & Googling[^], I suppose.

Veni, vidi, vici.

Re: mfc

David Crow6-Nov-13 4:13

David Crow

6-Nov-13 4:13

shizhanbiao wrote:
How to do it.

How to do what, exactly? Confused | :confused:

Create a dialog box with two buttons? Implement drag and drop? Swap two buttons? Be specific with what you are asking. It's Wednesday so the mind-reading pills are wearing off.

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"Show me a community that obeys the Ten Commandments and I'll show you a less crowded prison system." - Anonymous

Getting output parameters value[Solved]

pkfox4-Nov-13 4:04

pkfox

4-Nov-13 4:04

Hi all, I read some more on MSDN and found out that if you call a stored proc ( SQL Server in my case ) which returns a record set and also populates an *output* parameter , the parameters return value is in a separate record set. What I did was print all my records then move to the next set with:

spRst = spRst->NextRecordset();
// you also need to access the *Item* collection ( which I wasn't doing previously )
// then get the return value from the *command object*
bstr_t NumRecs = ((bstr_t)pCmd->Parameters->Item["Count"]->Value)->GetBSTR(); // this used to always return zero.

A lesson learnt.

Hi all, the code below works fine except for the retrieval of the @Count parameter which is of type *output* it always returns zero - any ideas ? ( it's this line of code : _tprintf(_T("Records found = %d\n\n"),spCmd->Parameters["@Count"]);

Many thanks

C++

#pragma region Includes and Imports
#include "stdafx.h"

#include <atlstr.h>

#import "C:\Program Files\Common Files\System\ADO\msado15.dll" rename("EOF","EndOfFile")
using namespace ADODB;
#pragma endregion

static ADODB::_ParameterPtr CreateParam(_bstr_t Name, _bstr_t Value, int Size, ADODB::DataTypeEnum Type, ADODB::ParameterDirectionEnum Direction);
static ADODB::_ParameterPtr CreateParam(_bstr_t Name, int Value, int Size, ADODB::DataTypeEnum Type, ADODB::ParameterDirectionEnum Direction);

int _tmain(int argc, _TCHAR* argv[])
{
if (argc < 4)
{
_tprintf(_T("Usage: CppUseADO.exe \"Search for this\" Y|N to specify combined or not Y|N to include address search\n"));
return -1;
}

int i = 0;
::CoInitializeEx(NULL, COINIT_APARTMENTTHREADED);

ADODB::_ConnectionPtr spConn = NULL;
ADODB::_RecordsetPtr spRst = NULL;
ADODB::_CommandPtr spCmd = NULL;
ADODB::_ParameterPtr spParam = NULL;

_bstr_t bstrSearchExp(argv[1]);
_bstr_t bstrCombined(argv[2]);
_bstr_t bstrSearchAddress(argv[3]);

_bstr_t bstrConn("dsn=CMS;");

try
{

spConn.CreateInstance(__uuidof(ADODB::Connection));
_tprintf(_T("Connecting to the database ...\n"));
spConn->Open(bstrConn, "", "", NULL);

spCmd.CreateInstance(__uuidof(ADODB::Command));

spCmd->ActiveConnection = spConn;
spCmd->CommandText = "SearchOnCreditorName";
spCmd->CommandType = ADODB::adCmdStoredProc;

spRst.CreateInstance(__uuidof(ADODB::Recordset));

spParam = CreateParam("@PartWord", bstrSearchExp, 35, ADODB::adVarChar, ADODB::ParameterDirectionEnum::adParamInput);
spCmd->Parameters->Append(spParam);

spParam = CreateParam("@Combined", bstrCombined, 1, ADODB::adChar, ADODB::ParameterDirectionEnum::adParamInput);
spCmd->Parameters->Append(spParam);

spParam = CreateParam("@SearchAddress", bstrSearchAddress, 1, ADODB::adChar, ADODB::ParameterDirectionEnum::adParamInput);
spCmd->Parameters->Append(spParam);

spParam = CreateParam("@Count", 0, 8, ADODB::adInteger, ADODB::ParameterDirectionEnum::adParamReturnValue);
spCmd->Parameters->Append(spParam);

_tprintf(_T("Searching the CMS Database for value %s \n"), (PCTSTR)bstrSearchExp);
spCmd->Prepared = true;

spRst = spCmd->Execute(NULL, NULL, NULL);

_tprintf(_T("Records found = %d\n\n"),spCmd->Parameters["@Count"]);

while (!spRst->EndOfFile)
{
variant_t vtClaimRef(spRst->Fields->Item["ClaimRef"]->Value);
variant_t vtCreditorName(spRst->Fields->Item["CreditorName"]->Value);
variant_t vtAddr1(spRst->Fields->Item["AddrLine1"]->Value);
variant_t vtAddr2(spRst->Fields->Item["AddrLine2"]->Value);
variant_t vtAddr3(spRst->Fields->Item["AddrLine3"]->Value);

_tprintf(_T("%s\t %s\t %s %s %s\n"),
vtClaimRef.vt == VT_NULL ? _T("(DBNull)") : (PCTSTR)vtClaimRef.bstrVal,
vtCreditorName.vt == VT_NULL ? _T("(DBNull)") : (PCTSTR)vtCreditorName.bstrVal,
vtAddr1.vt == VT_NULL ? _T("(DBNull)") : (PCTSTR)vtAddr1.bstrVal,
vtAddr2.vt == VT_NULL ? _T("(DBNull)") : (PCTSTR)vtAddr2.bstrVal,
vtAddr3.vt == VT_NULL ? _T("(DBNull)") : (PCTSTR)vtAddr3.bstrVal);

i++;
spRst->MoveNext(); // Move to the next record
}

_tprintf(_T("%d records printed for %s\n"), i, (PCTSTR)bstrSearchExp);

}
catch (_com_error err)
{
_tprintf(_T("\nOops something went wrong ! probably no records found\n"));
_tprintf(err.Description());
_tprintf(err.ErrorMessage());
_tprintf(_T("\n\n"));
}

/////////////////////////////////////////////////////////////////////////
// Clean up objects before exit.
//

_tprintf(_T("Closing the connection...\n"));

// Close the record set if it is open
if (spRst && spRst->State == ADODB::adStateOpen)
spRst->Close();

// Close the connection to the database if it is open
if (spConn && spConn->State == ADODB::adStateOpen)
spConn->Close();

::CoUninitialize();
return 0;
}

static ADODB::_ParameterPtr CreateParam(_bstr_t Name, _bstr_t Value, int Size, ADODB::DataTypeEnum Type, ADODB::ParameterDirectionEnum Direction)
{
ADODB::_ParameterPtr spParam;
spParam.CreateInstance(__uuidof(ADODB::Parameter));
spParam->Direction = Direction;
spParam->Name = Name;
spParam->Type = Type;
spParam->Size = Size;
spParam->Value = Value;
return spParam;
}

static ADODB::_ParameterPtr CreateParam(_bstr_t Name, int Value, int Size, ADODB::DataTypeEnum Type, ADODB::ParameterDirectionEnum Direction)
{
ADODB::_ParameterPtr spParam;
spParam.CreateInstance(__uuidof(ADODB::Parameter));
spParam->Direction = Direction;
spParam->Name = Name;
spParam->Type = Type;
spParam->Size = Size;
spParam->Value = Value;
return spParam;
}

C++

We can’t stop here, this is bat country - Hunter S Thompson RIP

modified 6-Nov-13 2:40am.

Re: Gettin output parameters value

Richard MacCutchan4-Nov-13 6:10

Richard MacCutchan

4-Nov-13 6:10

I cannot find a reference for the CreateParam function anywhere so it's difficult to check your settings. Also, it would help if you put <pre> tags around your code.

Veni, vidi, abiit domum

Re: Gettin output parameters value

pkfox4-Nov-13 10:07

pkfox

4-Nov-13 10:07

OK, sorry Richard ' the CreateParam function is a UDF , I included it in the code sample - also I didn't know about the

 tag
<div class="signature">We can’t stop here, this is bat country - Hunter S Thompson RIP</div>

Re: Gettin output parameters value

David Crow4-Nov-13 10:44

David Crow

4-Nov-13 10:44

pkfox wrote:
also I didn't know about the
tag

Select the text, and click either the "code" or "var" link above the message box. I would add to this that most of the code you've shown is not relevant to the problem. Only include what is absolutely necessary so that more folks will read your post.

Re: Gettin output parameters value

Richard MacCutchan4-Nov-13 22:29

Richard MacCutchan

4-Nov-13 22:29

Not the 'var' link for lines of code.

Veni, vidi, abiit domum

Re: Gettin output parameters value

Richard MacCutchan4-Nov-13 22:31

Richard MacCutchan

4-Nov-13 22:31