@Axel-Spoerl Thanks , I did post "sarcastic" ...." it compiles" in "the lounge".

Maybe I could ask for it to be moved .....

and do as you suggested after

@AnneRanch simplilfied() will squeeze possibly more spaces between bluetooth.service; and disabled into only one space. This will make sure contains() call more accurate.

@Chris-Kawa I did not realize I made a duplicate post , so I am adding my goof here . Sorry for wasting space.
I think I got the concept of containers, but I am obviously missing something else.

What am I missing in my code ?

Decaration

QList<const QBluetoothDeviceInfo* > RemoteDeviceInfo;

This works

RemoteDeviceInfo.append(&info);

// verify text = "!!!!!!!!! DEBUG verify RemoteDeviceInfo \n"; text += " name \n"; text += RemoteDeviceInfo.at(0)->name(); qDebug() << text; m_ui->plainTextEdit_8->appendPlainText(text); // m_ui->plainTextEdit_3->appendPlainText(text for(auto &device:RemoteDeviceInfo) { text = " BUILD range loop test "; m_ui->plainTextEdit_8->appendPlainText(text); text = " device name "; text += device->name(); m_ui->plainTextEdit_8->appendPlainText(text); }

when I attempt to verify RemoteDeviceInfo) using another method

it fails

if(!RemoteDeviceInfo.isEmpty()) passes OK
{
for (auto &device:RemoteDeviceInfo)
{
text = " For loop test ";
qDebug() << text;
text = " device address \n";
text += device->address().toString(); fails here
qDebug() << text;
m_ui->plainTextEdit_8->appendPlainText(text);
text = " device name \n";
text += device->name(); // >address().toString()
qDebug() << text;
m_ui->plainTextEdit_8->appendPlainText(text);

} } }

My debug shows no contents in RemoteDeviceInfo when used in another method.

@Andy314 said:

Strange it comes with the new Qt-version
QMAKE_CXXFLAGS += -permissive

Qt6 requires C++17 and requires permissive- switch in MSVC (not to confuse with -permissive, which is the same as /permissive). Further C++ standards in MSVC imply permissive- and are required for some of the new features like modules or concepts. Qt6 requires it to avoid having to support non-standard code paths for a single supported compiler.

permissive- switch turns off all language extensions and makes the implementation conformant with the standard.

As @kshegunov said, you should not be using permissive. It locks you into MSVC specific toolchain and will make updates to future standards harder and error prone.
I'd say keep the standard conformance on and fix code that is nonstandard.

@Chris-Kawa

We were beyond floppies by then. The first computer I used had 10.5 inch (I think, unless it was only 8 inch) floppies, https://www.computinghistory.org.uk/det/10247/Nord-ND305-355-Floppy-Disk/ :)

@AnneRanch I did not realize that pairingFinished( emulates the SIGNAL.
I get compiler warning that it is missing "emit" , which is kind of
superficial if it generates SIGNAL without "emit".

localDevice.requestPairing(adapter.address(), QBluetoothLocalDevice::AuthorizedPaired); localDevice.pairingFinished(adapter.address(), QBluetoothLocalDevice::Pairing());

PARTIALLY SOLVED

@kshegunov said in question about singletons:

static variables inside a function are automatically thread-safe (since C++11). A class variable is not automatically thread-safe.

No they aren't. Only the initialization is thread-safe, which is also guaranteed for any global static (scoped or not).

Thank you for clarifying this. It is what I meant (but not what I wrote).

@JonB Thanks but no, I had a wrong syntax.
SOLVED

@AR --

You are going to keep having problems with these embedded command line sequences. quoting/escaping embedded command sequences is a PITA, and can be mitigated by creating subshell scripts and just calling the script instead of trying to build a long convoluted command line on execution. It also has the benefit of allowing for easier testing because you can work out the script directly and not involve Qt until you are ready.

@nasimChildOfDesert said in Sqlite connection QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.:

threading, mutex, socketprograming TCP

You don't need threading for sockets/tcp when you use Qt. Seaching for 'Qt threading' or looking at the QTcpSocket documentation should be a good start.

Here is an update.
Went back to project backup copy and got rid of the gibberish.

The result of the "ln" ( '/dev/rfcomm0' -> '/dev/ttyUSB0' ) is now in the temporary file
which resides in my main .pro folder .
Do not like it there , but...

I like to redirect good "ln" result into QString using stdio - if possible-
,and error too.
I am working on that but could still use some assistance to add that to the current command.

"TASK unlink "
" echo q | sudo -S -k unlink /dev/rfcomm0 "
[sudo] password for nov25-1: " echo q | sudo -S -k unlink /dev/rfcomm0 SUCCESS un linked "
" Result system 0"
"TASK link - add tee "
" echo q | sudo -S -k ln -s -v /dev/ttyUSB0 /dev/rfcomm0 | tee temporary_link_file.txt"
[sudo] password for nov25-1: '/dev/rfcomm0' -> '/dev/ttyUSB0'
" echo q | sudo -S -k ln -s -v /dev/ttyUSB0 /dev/rfcomm0 | tee temporary_link_file.txt SUCCESS linked "
" Result system 0"

@mzimmers

Unless I'm misreading the thread, there is a fundemental difference between a class trait object and an inherited class. you can't get "parent" of a trait object and expect it to be the class where the trait is instantiated.

When using pure inheritence, you can refer to parent(), but you better use the correct type cast operation when doing so.

IOW, parent or superclass access works for is_a, but not for has_a.

@JonB I would agree with Kent, avoid. It's far too easy to blow past the stack size with this with no warning. With constant sizes you can static check this. With dynamic containers you use the heap, so no problem either. With this you never know.
It's also worth mentioning that it makes stuff like sizeof become a runtime evaluation instead of a constant compile time expression, so another potential downside. I'd say being explicit about your stack usage is always a good thing and leaving it to runtime parameters is asking for trouble.
Besides, it's a compiler extension, so locking you into that particular brand. Something I would avoid too.

@JoeCFD The stack sizes are a per thread resource, yes, but they allocate address space and physical memory pages can be mapped as needed. A modern PC runs hundreds of threads at a time and it's easy to get into GB territory of address space allocations just for stacks, even if physical memory use is a lot lower. Large stacks can be an issue where address space is limited, e.g. on 32 bit systems, or can lead to degraded performance due to large amount of small chunks and fragmentation. The stack size is a balancing act. The defaults are different on different platforms, but you can always set your own size for your app. If you know it's stack hungry or that it barely uses it and you have a lot of threads running you can configure stack size via compiler switches.

@AnneRanch
You have to set the break point in the implementation, i.e. usually the cpp file.
The constructors listed are definitions ;-)
You probably want to debug the first one, which takes only a parent argument.

@KuQt said in : Syntax:

:Animal(age)

As @Christian-Ehrlicher says about readable code tags, please. Which : Animal(age), you mean in

inline Dog(int age) : Animal(age)

? So that constructor is calling the base Animal constructor passing in the age it received? My knowledge of C++ is not perfect :), but without that wouldn't it look for a base constructor of plain Animal(), which does not exist?

@SGaist Thanks

Multi apps doing more work was less false sharing related.

Running multi apps with identical task and less threads seems like good trick to test performance with reduced false sharing vs memory bandwidth.

Now placed for loops and data in a way to attemp maximize multithreaded memory access distance between threads instead of closeness for portions involving writing data while keeping memory access closeness and less copies for reading portions.

Hopefully that is right philosophy for multithreaded optimization on multilevel cached hardware.