C / C++ / MFC Discussion Boards

Re: c++ - std :: map - Is my idea too dirty?

Jochen Arndt12-Jul-18 23:13

12-Jul-18 23:13

I'm a bit late to the party.

The key point of a map is that no two elements in a map container can have equivalent keys. If the number of significant digits entered is less than the precision of double values, this will not happen (besides entering the same value again which applies to ints as well).

But you might get problems when trying to access elements by key when the argument is from other sources (affected by rounding).

That would be my bad feeling:
While there is no problem with the map itself, key based operations ([]operator, erase, swap, find) might behave not as expected (no match). Even when not using such operations now but only iterator based ones, they may be used later when updating the code. So you should at least place a comment about this.

Another option is creating your own std::map based class that disables the affected operations or replaces them with a version that treats close numbers as identical (defining an epsilon).

Re: c++ - std :: map - Is my idea too dirty?

User 1106097913-Jul-18 6:54

User 11060979

13-Jul-18 6:54

Thank you very much for your comments and your time.

It does not solve my Problem, but it answers my question

modified 19-Jan-21 21:04pm.

Re: c++ - std :: map - Is my idea too dirty?

Randor 23-Jul-18 12:20

Randor

23-Jul-18 12:20

0x01AA wrote:
std :: map<double, MyType, std :: less<double> >

Hi,

I was avoiding this discussion but I wanted to just add one more comment. The FPU has a state that has an affect on the precision. In other words... when the FPU is in various states you get a different rounding value. You can control this state with _controlfp_s

Printer DLL and other libraries outside of your control could potentially change the thread FPU state causing your std::map to contain multiple floating point numbers from the same calculations. Unfortunately on Windows user-applications cannot always control third-party DLL from loading into your process. Those DLL could modify and then fail to reset the floating point state.

The answer is "Yes" what you are proposing would work 99% of the time or in "laboratory" conditions where you control both the hardware and software. But if you tried to ship out a commercial product using the above technique... you will almost certainly have a small percentage of the conditions I described above.

Best Wishes,
-David Delaune

Re: c++ - std :: map - Is my idea too dirty?

User 1106097923-Jul-18 20:48

User 11060979

23-Jul-18 20:48

Wow, great that you share this knowledge.
Thank you very much for this.

It does not solve my Problem, but it answers my question

modified 19-Jan-21 21:04pm.

need COM/DCOM basics

Sakthiu11-Jul-18 3:35

Sakthiu

11-Jul-18 3:35

Hi,

I need basics to know about COM/DCOM. Any good article, please point me the link

Thanks,

Re: need COM/DCOM basics

jeron111-Jul-18 4:07

jeron1

11-Jul-18 4:07

There are several articles on CodeProject, here are links to a few;
DCOM D-Mystified: A DCOM Tutorial, Step 1[^]
Introduction to COM - What It Is and How to Use It.[^]
The Simplest COM Tutorial in Visual Studio 2008[^]
DCOM D-Mystified: Questions and Answers[^]
COM in plain C[^]

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Global key press [SOLVED]

Valentinor14-Jul-18 18:38

Valentinor

14-Jul-18 18:38

Hi,

What is the recommended way to listen for a key press globally? At first, adding an infinite loop came to mind (for(;;), or while(true)), but these are bad choices, as they eat a lot of CPU, and adding sleep will cause to lose some of the key press events.
I want to make it to check any key (or key combination), to see what is pressed on Windows OS.

Re: Global key press

Jochen Arndt10-Jul-18 2:45

Jochen Arndt

10-Jul-18 2:45

It depends if "globally" applies to the system (user session) or an application. For an application it depends on the type (console or GUI). With GUI applications it depends also if you want to catch all / multiple or only a single / few key combinations.

The most "global" method is hooking keyboard events with SetWindowsHookEx function (Windows)[^].

For application level handling see About Keyboard Input | Microsoft Docs[^] and follow the links.

To handle only a few specific keyboard events for GUI applications use Accelerators (Hotkeys) processed by the main window of the application.

Re: Global key press

Valentinor10-Jul-18 8:29

Valentinor

10-Jul-18 8:29

This function will be called from Java, which app will be minimized, or maybe running in the background. The app won't be focused, so yes, I need it for the entire user session, even if another application is focused, I want it to still register the key press and do something in case a key I randomly choose is pressed. I will make some profiles: profile 1 has key "A", profile 2 has key "CTRL + A", those combinations will be changeable.

Re: Global key press

Jochen Arndt10-Jul-18 21:21

Jochen Arndt

10-Jul-18 21:21

You might have a look at the AutoIt Scripting Language. I guess you can use that to do what you want.

In any case you should not use a key combination that is used by Windows itself or common applications. See Keyboard shortcuts in Windows for a list of combinations that should not be redirected.

Re: Global key press

Randor 10-Jul-18 23:53

Randor

10-Jul-18 23:53

Valentinor wrote:
I want it to still register the key press and do something in case a key I randomly choose is pressed. I will make some profiles: profile 1 has key "A", profile 2 has key "CTRL + A",

Sounds like you are looking for the RegisterHotKey function[^].

Best Wishes,
-David Delaune

Re: Global key press

Valentinor11-Jul-18 5:09

Valentinor

11-Jul-18 5:09

For what I have now, I'll use only one key, and I used "SetWindowsHookEx". Is it possible to use that for a combination of keys? I don't need it in this application, but in future I will need it. All the examples I saw on google were with only 1 key, or using the mouse. If you can use it for key combination, can it be used to combine 4-5 keys? Yes, it is hard to press that many at a time, but you can map an extra key from the keyboard to press all of them at the same time.

Thanks for you help!

Re: Global key press

Jochen Arndt11-Jul-18 6:40

Jochen Arndt

11-Jul-18 6:40

With key combinations I meant a combination of a single key while also Shift, Ctrl, and or Alt are down.

A combination of multiple keystrokes makes no sense because that can't be "eaten" (the initial strokes has to be passed and will be processed by the window having the focus).

It is still unclear what you finally want to do. If is not a personal project, be very careful what you are doing. Such global "features" might interfere with the active application which is a "don't do it".

Re: Global key press

Valentinor13-Jul-18 20:45

Valentinor

13-Jul-18 20:45

So, let me reformulate my last statement.
What is the alternative of SetWindowsHookEx, for a combination of keys, by checking if Ctrl and/or Alt and/or Shift is down + any other key (different from Windows combinations)?
For a single button (keyboard or mouse) it is great, but from what I've seen, it can't be used to check at the same time if any Ctrl, Alt, Shift is down.

Re: Global key press

Jochen Arndt13-Jul-18 21:00

Jochen Arndt

13-Jul-18 21:00

The status of the Alt key is passed to the hook callback. The status of the Shift and Ctrl keys (and any other key) can be determined with the GetKeyState function (Windows)[^].

Re: Global key press

Valentinor14-Jul-18 10:58

Valentinor

14-Jul-18 10:58

Ok, thanks!

OnDeviceChange dbcc_name length

Member 138991789-Jul-18 4:34

Member 13899178

9-Jul-18 4:34

Hello,

I have registered USB serial devices for notification and get a device arrival & removal notice now in OnDeviceChange. However, always when I try to print out the dbcc_name, its length is one wide character (as defined in the structure documentation) and nothing more prints out. I have browsed countless examples where the code proceeds to extract for instance a VID/PID from the string. What am I doing wrong? The examples also give me one character. I am using windows 10 & VS2017.

I have even reserved a larger buffer for notification registration to fit in the full dbcc_name string. Nothing helps, just get that one character. I have also tried the WideCharToMultibyte and then instead of a Chinese character I get a single question mark. Please advise.

Re: OnDeviceChange dbcc_name length

Richard MacCutchan9-Jul-18 5:26

Richard MacCutchan

9-Jul-18 5:26

Quote:
I am using windows 10 & VS2017.

Yes, but we cannot guess what code you are using. Please edit your question and provide full details.t

Re: OnDeviceChange dbcc_name length

Member 138991789-Jul-18 20:37

Member 13899178

9-Jul-18 20:37

I am using MFC & C++. This code is missing the WideCharToMultibyte conversion which didn't help one bit. I am using this document as refrence: http://www.ftdichip.com/Support/Documents/AppNotes/AN_152_Detecting_USB_%20Device_Insertion_and_Removal.pdf

BOOL CTesterDlg::OnDeviceChange(UINT nEventType, DWORD_PTR dwPtrData)
{
	BOOL bReturn = CWnd::OnDeviceChange(nEventType, dwPtrData);

	PDEV_BROADCAST_DEVICEINTERFACE b = (PDEV_BROADCAST_DEVICEINTERFACE)dwPtrData;

	if(b != NULL)
	{
		CString Msg;
		Msg.Format(L"%s",b->dbcc_name);
		MessageBox(Msg);
	}

	switch (nEventType)
	{
		case DBT_DEVICEARRIVAL:
			if(hComm==INVALID_HANDLE_VALUE) DeviceInit();
			break;
		case DBT_DEVICEREMOVECOMPLETE:
			ClosePort();
			break;
	}

	return bReturn;
}

Re: OnDeviceChange dbcc_name length

Richard MacCutchan9-Jul-18 21:04

Richard MacCutchan

9-Jul-18 21:04

Use your debugger to see exactly what is returned in Dbcc_name. The code looks correct but the actual data may be the problem.

Re: OnDeviceChange dbcc_name length

Member 138991789-Jul-18 21:06

Member 13899178

9-Jul-18 21:06

Yeah, there is nothing more with my debugger than is in the MessageBox added for debugging purposes.

Re: OnDeviceChange dbcc_name length

David Crow9-Jul-18 16:24

David Crow

9-Jul-18 16:24

Member 13899178 wrote:
However, always when I try to print out the dbcc_name, its length is one wide character (as defined in the structure documentation) and nothing more prints out.
...
Please advise.

Please provide the code you are using to do the printing.

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Re: OnDeviceChange dbcc_name length

Jochen Arndt9-Jul-18 22:57

Jochen Arndt

9-Jul-18 22:57

The handler is called multiple times for a single event with different parameters, and also upon specific device changes even when not registered. So you have to check always if the device type matches and cast then to the corresponding broadcast structure (because all structures have the common _DEV_BROADCAST_HDR | Microsoft Docs[^] header, casting can be done initially when checking for the matching type).

So your code should look like (based on your code snippet posted in the above sub thread):

C++

// FTDI_D2XX_Device Class GUID
// To be used with RegisterDeviceNotification()
/*static*/ const GUID CTesterDlg::GUID_DEVINTERFACE_FTDI_D2XX =
{ 0x219D0508, 0x57A8, 0x4FF5, { 0x97, 0xA1, 0xBD, 0x86, 0x58, 0x7C, 0x6C, 0x7E }};

BOOL CTesterDlg::OnDeviceChange(UINT nEventType, DWORD_PTR dwPtrData)
{
    BOOL bReturn = CWnd::OnDeviceChange(nEventType, dwPtrData);

    PDEV_BROADCAST_DEVICEINTERFACE b = reinterpret_cast<PDEV_BROADCAST_DEVICEINTERFACE>(dwPtrData);
    // Check if dwPtrData is not NULL and for type BROADCAST_DEVICEINTERFACE.
    // When having registered an event with a GUID, that should be also compared here.
    // Comparing the GUID must be done when having registered multiple events.
    if (b && 
        b->dbcc_devicetype == DBT_DEVTYP_DEVICEINTERFACE &&
        b->dbcc_classguid == GUID_DEVINTERFACE_FTDI_D2XX)
    {
        //MessageBox(b->dbcc_name);

        // Handle events here
        // switch (nEventType)
    }
    return bReturn;
}

Regarding the encoding of the name, see _DEV_BROADCAST_DEVICEINTERFACE_A | Microsoft Docs[^]:

Quote:
When this structure is returned to a window through the WM_DEVICECHANGE message, the dbcc_name string is converted to ANSI as appropriate.

That means you will get an ANSI string with ANSI builds and a Unicode string with Unicode builds when having called RegisterDeviceNotification().

Portions of the above (like the GUID) are from some testing code I have written in 2012 where I have logged the name using

// Log using the full name from device change notification.
App()->Log(TRACE_LOG_DEBUG,
    _T("Device %s has been %s"), 
    pDev->dbcc_name,
    nEventType == DBT_DEVICEARRIVAL ? _T("added") : _T("removed"));

As far as I remember, the name was displayed properly .

Re: OnDeviceChange dbcc_name length

Member 138991789-Jul-18 23:26

Member 13899178

9-Jul-18 23:26

All valid points, thank you. The note about device interface was good and got me on the right track. I was blind to that part as the code seemed to work and returned something. The problem seems to have been that I have registered to receive messages to my Hwnd from GUID_DEVCLASS_PORTS which is not an interface class, now I changed to GUID_DEVINTERFACE_USB_DEVICE and I get a proper string with VID & PID. Problem solved, thanks!

Re: OnDeviceChange dbcc_name length

Jochen Arndt9-Jul-18 23:42

Jochen Arndt

9-Jul-18 23:42

Fine to hear that the problem is solved.

If you don't need the VID and PID but just want to be informed of the plugin / -out for the virtual COM ports, there is even no need to register. Then just check for DBT_DEVTYP_PORT events. They are one of the always signaled events (as already mentioned):

// Assume port changing (serial or parallel). The devicetype field is part of header of all structures.
// The name passed here is always the COM port name (even with virtual ports).
// Note that dwData may be NULL.
PDEV_BROADCAST_PORT pPort = reinterpret_cast<PDEV_BROADCAST_PORT>(dwData);
if (pPort && DBT_DEVTYP_PORT == pPort->dbcp_devicetype)
{
    // pPort->dbcp_name is "COMx" or "LPTx"
}

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