Managed C++/CLI

Re: How to check availability of internet connection

11-Dec-08 3:00

Hi I have an SQL query which is to be executed from the server. Just before executing, I am checking if the internet is available or not.

I am using InternetGetConnectedState api to implement this.

But this call returns true, for 2-3 seconds after the network connection is lost. This causes the application to hang.

Pls verify my code and check if it is the appropriate code

---------------------------------------------------

[DllImport("wininet.dll",
SetLastError=true,CharSet=CharSet::Unicode,ExactSpelling=true,
CallingConvention=CallingConvention::StdCall)]
static bool InternetGetConnectedState(int &Description, int ReservedValue ) ;

bool IsConnectedToInternet()
{
int Desc ;
return InternetGetConnectedState(Desc, 0 ) ;
}

if (IsConnectedToInternet())
{
mysql_query(mysqlConnectorObject,sqlQuery);
return mysql_store_result(mysqlConnectorObject);
}
else
{
MessageBox::Show("Not connected");
}

----------------------------------------------------

Thanks in advance

Anvesh

Luc Pattyn11-Dec-08 3:16

Re: How to check availability of internet connection

11-Dec-08 3:16

Hi,

InternetGetConnectedState() is the best way I know to look at the Internet connection state.

You are saying it shows a slightly outdated state, but that should not be too bad. Anyway,
the connection could be lost right after you call the function, so the code that follows must
survive that anyway. Hence, use asynchronous code (on a separate thread) and give whatever you
are trying to do a timeout.

Smile | :)

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anveshvm11-Dec-08 4:12

Re: How to check availability of internet connection

11-Dec-08 4:12

Thank you very much.....

Can you pls tell me how to set the time limit when starting a new thread.

Can you also suggest the most suited class to do this? I mean whether it is backgroundworker, threadpool or thread class?

Luc Pattyn11-Dec-08 4:36

Re: How to check availability of internet connection

11-Dec-08 4:36

anveshvm wrote:
how to set the time limit

you either perform calls that support a time limit, or you should launch a (one-shot) timer, which:
- you cancel again when the operation succeeds
- and if the timer fires, you stop the timer and cancel the thread

anveshvm wrote:
backgroundworker, threadpool or thread?

whatever fits your circumstances best; since you may have to abort it, threadpool could not be the right choice though.

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anveshvm11-Dec-08 4:42

Re: How to check availability of internet connection

11-Dec-08 4:42

Thank you Luc Pattyn.... I will try that way. Smile | :)

Luc Pattyn11-Dec-08 13:29

How to check the return value of a messagebox

11-Dec-08 13:29

Hi,

I just discovered this article[^] that may interest you.

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anveshvm11-Dec-08 2:52

Re: How to check the return value of a messagebox

11-Dec-08 2:52

I have written a code to check the return value of a message box. But it doesn't work .

My code is
--------------------------------------

DialogResult^ res = MessageBox::Show("Network connection failed.,"Error in connection",MessageBoxButtons::RetryCancel,MessageBoxIcon::Warning,MessageBoxDefaultButton::Button1);

if (res == System::Windows::Forms::DialogResult::Cancel)
{
Application::Exit();
}
else if (res == System::Windows::Forms::DialogResult::Retry)
{
continue;
}

---------------------------------------------------------

Here both the if condition fails...

In immediate window, the value of res is {...}

Pls check it

Thanks in advance

Anvesh

Luc Pattyn11-Dec-08 3:10

Re: How to check the return value of a messagebox

11-Dec-08 3:10

anveshvm wrote:
DialogResult^ res

do you want the ^ there? DialogResult is a value type, isn't it?

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anveshvm11-Dec-08 3:31

Re: How to check the return value of a messagebox

11-Dec-08 3:31

Yeah.... I got it....

Thanks alot

Luc Pattyn11-Dec-08 3:43

How to call base class method

11-Dec-08 3:43

you're welcome.

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s196675m8-Dec-08 8:54

s196675m

8-Dec-08 8:54

From inside the overriden virtual function of a derived class, how can I call the base class function. The C# equivalent is base.SomeVirtualFunction(); I need VC++ managed equivalent.

Thank you.

Re: How to call base class method

Mark Salsbery8-Dec-08 9:51

Re: How to call base class method

8-Dec-08 9:51

public ref class baseclass
{
public:
    virtual void virtualmethod()
    {
    }
};

public ref class derivedclass : public baseclass
{
public:
    virtual void virtualmethod() override
    {
        baseclass::virtualmethod();
    }
};

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

Eytukan12-Dec-08 19:49

Eytukan

12-Dec-08 19:49

You know it's really funny. C++/CLI forum is serving every other forum. All platform related things are being asked here taking the burden off C# & VB.net forums, and also the OO questions, freeing up the C++ forum Big Grin | :-D

OK,. what country just started work for the day ? The ASP.NET forum is flooded with retarded questions. -Christian Graus

Best wishes to Rexx[^]

Re: How to call base class method

Mark Salsbery13-Dec-08 6:52

Getting HDD serial No in C++/CLI environment

13-Dec-08 6:52

This board is so dead it makes me Sleepy | :zzz:

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

J_E_D_I5-Dec-08 21:50

5-Dec-08 21:50

Hi, I had this code which worked beautifully in console mode, but now I am trying to convert the program into windows forms and the compiler returns the following error:

Error 1 error C3861: '_T': identifier not found

Any advice on how to solve this problem would be highly appreciated.

int GetHDDserialNo;

	//// Gets HDD serial No
	TCHAR volumeName[MAX_PATH];
	DWORD volumeSerialNumber;
	DWORD maxNameLength;
	DWORD fileSystemFlags;
	TCHAR systemName[MAX_PATH];

	GetHDDserialNo = GetVolumeInformation
		(
		_T("c:\\"),
		volumeName, MAX_PATH,
		&volumeSerialNumber,
		&maxNameLength,
		&fileSystemFlags,
		systemName, MAX_PATH
		);

	int SerialNumber = volumeSerialNumber;

Mark Salsbery6-Dec-08 6:12

6-Dec-08 6:12

J_E_D_I wrote:
'_T': identifier not found

#include <tchar.h>

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

J_E_D_I6-Dec-08 9:07

6-Dec-08 9:07

Thanks, I do not get that error anymore...but I get all those ones!

Error 1 error C2065: 'MAX_PATH' : undeclared identifier
Error 2 error C2065: 'DWORD' : undeclared identifier
Error 3 error C2146: syntax error : missing ';' before identifier 'volumeSerialNumber'
Error 4 error C2065: 'DWORD' : undeclared identifier
Error 5 error C2146: syntax error : missing ';' before identifier 'maxNameLength'
Error 6 error C2065: 'maxNameLength' : undeclared identifier
Error 7 error C2065: 'DWORD' : undeclared identifier
Error 8 error C2146: syntax error : missing ';' before identifier 'fileSystemFlags'
Error 9 error C2065: 'fileSystemFlags' : undeclared identifier
Error 10 error C2065: 'MAX_PATH' : undeclared identifier
Error 11 error C2065: 'maxNameLength' : undeclared identifier
Error 12 error C2065: 'fileSystemFlags' : undeclared identifier
Error 13 error C2065: 'systemName' : undeclared identifier
Error 14 error C2065: 'MAX_PATH' : undeclared identifier
Error 15 error C2078: too many initializers

Mark Salsbery6-Dec-08 9:36

6-Dec-08 9:36

What other header files are you including?

Those errors indicate windows.h is not included.

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

J_E_D_I6-Dec-08 19:58

6-Dec-08 19:58

Actually, windows.h is already included in the .cpp file...

These are the other header files I've got:

#include "stdafx.h"
#include "Form1.h"
#include tchar.h
#include vector
#include ctime
#include math.h
#include fstream
#include string
#include iostream
#include sstream
using std::dec;
using std::hex;
#include iomanip 
using std::setprecision; 
using std::setbase;
#include cstdlib
using std::atof;
#include windows.h
#pragma comment(lib, "user32.lib")
#include stdio.h
#include cstdio
#include strsafe.h
using namespace Ex22_01;

(Note: I had to remove < and > from the directives as otherwise it would not show up in this message)

Luc Pattyn7-Dec-08 1:14

7-Dec-08 1:14

Hi,

it may come as a surprise, but the order of the includes matters too.
i.e. if tchar.h relies on windows.h, then windows.h must precede tchar.h;
normally if you suddenly need another include, you put it at the end of the list.

BTW: the behavior of message editing regarding < and > depends on the checked state of "Ignore HTML tags in this message" checkbox.

Smile | :)

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J_E_D_I7-Dec-08 19:21

7-Dec-08 19:21

Luc, you are absolutely right! I've changed the order of the include directives and it works like a breeze.
Thank you so much for this, I admit I would have never thought about it.
Smile | :)

Luc Pattyn7-Dec-08 23:06

Re: Creating Registry Key Values in C++/CLI environment

7-Dec-08 23:06

You're welcome.

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J_E_D_I13-Dec-08 7:56

Re: Creating Registry Key Values in C++/CLI environment

13-Dec-08 7:56

Hi again Luc, I was wondering if you had any hint on how to solve this problem which is somehow linked to the previous one. I need to save the value obtained with the previous code (which is a DWORD: DesiredValue) in a registry key and this was the syntax I was using (successfully) in console environment.

DWORD DesiredValue;

// Creates Desired Registry Key 
	HKEY Xtmpkey;
	DWORD dwDisp = 0;
	LPDWORD xlpdwDisposition = &dwDisp;
	DWORD dwVal = DesiredValue; 
	// Desired Path for the Registry Key 
	RegCreateKeyEx(HKEY_CURRENT_USER, L"SOFTWARE\\MyPath", 0L,NULL, REG_OPTION_NON_VOLATILE, KEY_ALL_ACCESS, NULL, &Xtmpkey,xlpdwDisposition);

// Creates Desired Value
RegSetValueEx (Xtmpkey, L"Desired_Value_Name", 0L, REG_DWORD,(CONST BYTE*) &dwVal, sizeof(DWORD));

Now that I am porting the software into C++/CLI environment it returns the following errors:

Error 1 error LNK2001: unresolved external symbol "extern "C" long __stdcall RegCreateKeyExW(struct HKEY__ *,wchar_t const *,unsigned long,wchar_t *,unsigned long,unsigned long,struct _SECURITY_ATTRIBUTES * const,struct HKEY__ * *,unsigned long *)" (?RegCreateKeyExW@@$$J236YGJPAUHKEY__@@PB_WKPA_WKKQAU_SECURITY_ATTRIBUTES@@PAPAU1@PAK@Z)

Error 2 error LNK2001: unresolved external symbol "extern "C" long __stdcall RegSetValueExW(struct HKEY__ *,wchar_t const *,unsigned long,unsigned long,unsigned char const *,unsigned long)" (?RegSetValueExW@@$$J224YGJPAUHKEY__@@PB_WKKPBEK@Z)

Error 3 fatal error LNK1120: 2 unresolved externals

What am I doing wrong?

I thank you in advance.

Luc Pattyn13-Dec-08 8:26