Planned maintenance has been done but it did not solve the problem. So work will continue on this and a new time for trying updates will be announced asap.
@adutzu89 said in Stack/Heap/smart pointers question.:
So what's the point of using a smart pointers instead of stack-based allocation?
The point is that you can't allocate everything on the stack.
So, often you have to use heap and then smart pointers should be used to make sure memory is freed again.
Every "new" requires "delete" at some point and that's exactly what smart pointers are used for.
@sierdzio said in compiler optimization:
I have no idea if it matters in this case, though.
A great deal. QString has an additional indirection through the d_ptr and this is the great wall of china standing in front of the optimizations the compiler could possibly make.
@Engelard this involves Windows API functions which find the window from the cursor point, possibly with WindowFromPoint which returns an HWND. From that HWND you can resolve the parent process with GetProcessHandleFromHwnd.
At the core of Windows applications is the message loop within which it calls a callback function, or window procedure, to handle event messages. There's a function called SetWinEventHook which allows intercepting certain window messages in a given range.
Now, if fraps can get the HWND of your app it can either intercept the WM_PAINT message to get a device context to draw over the top of the content, or it could create a child window displaying the FPS. But those are guesses.
Other than what I've speculated on, if you want to find out what's actually happening, you could use OllyDbg to reverse engineer the program.
@SGaist said in Statistics c++:
histogram from the frequencies of cats running through a street by moonless night
I have been scouring the internet for this! 😉
@JonB said in Simple big-looped program break down:
Doesn't "doubling" mean "the next power of 2"?
Yeah. I'm not at the top of my game, so you can probably safely ignore me.
@KroMignon said in How to use Qt documentation?:
@Please_Help_me_D said in How to use Qt documentation?:
In reality I also need to use Little/Big conversation with float data-type. Do you know how to solve that?
As far as I know, a float is stored as a 32 bits word and a double as 64 bits word.
So my suggestion would be to cast your float value to quint32 and your double to quint64
float floatBE = static_cast<float>(qToBigEndian(static_cast<quint32>(val));
double doubleBE = static_cast<double>(qToBigEndian(static_cast<quint64>(valDouble));
nope, that does NOT work! Casting float to int truncates it. What you can do instead, is to reinterpret_cast the memory occupied by the float - or use a union. We currently have a similar topic in the forum on this.
Regards
@Please_Help_me_D said in General question about arrays and I/o:
I need to extract {4, 2, 3}
You will need to do it by yourself. There is nothing for that neither in Qt nor in C++ stdlib. Even if there would be it would do nothing else as iterating over {4, 2, 3} in a loop. So, I doubt you can optimise here much.
@KroMignon said in QList and smart pointers:
auto obj=QSharedPointer<MyCustomObj>(new MyCustomObj, &QObject::deleteLater);
Your post interested me. I read some articles on this and I get the idea that you should not mix ownership methods. QObject based system uses parent/child to express ownership. So if you use smart pointers you should not use the parent/child ownership. I explored your custom deleter strategy with std smart pointers:
{
// smart pointers combined with custom deleter for use with QObject based objects
using namespace std;
shared_ptr<QObject> ptr(new QObject, [](QObject* p){
p->deleteLater();
});
unique_ptr<QObject,function<void(QObject*)>> ptr2(new QObject, [](QObject* p){
p->deleteLater();
});
}
I am filing this away for future use. Thanks for sharing.
Hi and welcome to devnet,
Where is your threading code ?
What do you do in it ?
Are you creating widgets in that thread ? If that's the case then it's wrong. Widgets creation and manipulation should be done in the QApplication thread i.e the main thread
@kshegunov said in Returning unique_ptr and preventing move:
The typical problem being that returning the unique_ptr transfers ownership.
I am confused then. I thought he had trouble doing this. I didnt understand that he didnt want it to move.
@Exotic_Devel said in Setters with and without this pointer.:
@J-Hilk said in Setters with and without this pointer.:
But why would you insist on always writing this-> this isn't Python !
Habit I acquired when I started using Java. :)
Ah, my condolences!
😉
The only way I see to write this "genericly" would be to have some virtual QVariant getValue() const and virtual QVariant setValue(QVariant v) in your base class and implement it in Derived.
This way you wouldn't have to do any casting, simply b2->setValue(b1->getValue()).
The implementation in Derived would do the cast to T via QVariant's value().
@Exotic_Devel In the link I posted is a full list of implicitly shared classes: list of classes. What I said applies to all of them and yes, QMap is one of them.
@mrdebug said in How to resolve this warning:
QtAndroid:
Wait, this is a warning and not an error?
Maybe a declaration to satisfy the template?:
void QAndroidJniObject::callMethod(const char *methodName, const char *sig, ...) const;
I don't know if that is the right sig though:
https://doc.qt.io/qt-5/qandroidjniobject.html#callMethod-1
@Vinoth-Rajendran4
Depends what you mean by "class memory", but as you say a static variable is never part of a class instance, so it will be stored (once) outside of any memory area allocated on creating an instance. Yes, it can be accessed across objects/instances precisely because it's in some shared area.
These are the instruction that I made after installed it on my Ubuntu 18.04 linux install. Maybe it will help you
Download QT 5.12.4 from QT website using the downloads buttons and then select open source and download
After Download is complete go to Downloads folder and run the installer
(for new ubuntu users – right click on file in downloads and select permissions and select option at bottom)
Download latest QT that is known to have LTS (long term support)
-Run installer
-deselect android stuff and make sure that you select the dev tools and sources at the bottom
install QT
download and install mysql and dev packages
sudo apt-get install libglu1-mesa-dev
sudo apt-get install build-essential
sudo apt-get install libmysqlclient-dev
sudo apt-get install libssl-dev
navigate to your Qt folder/5.12.4/Src
-run config file
-./configure -plugin-sql-mysql
Navigate to qt source ie...Qt/5.12.4/Src/qtbase/src/plugins/sqldrivers/mysql
-run the QT qmake
/home/bj/Qt/5.12.4/gcc_64/bin/qmake MYSQL_PREFIX=/usr/include/mysql/ mysql.pro
locations may vary depending on where you installed Qt during the installation process and what version of Ubuntu you may be using
after running qmake
-run make
-make install
you should be set from here...if you have any more issues then refer to these articles to seek clarification
https://forum.qt.io/topic/59449/qsqldatabase-qmysql-driver-not-loaded-build-mysql-plugin
https://stackoverflow.com/questions/37369480/qsqldatabase-qmysql-driver-not-loaded-on-ubuntu-15-04-64bits
https://doc.qt.io/qt-5/sql-driver.html#qmysql-for-mysql-4-and-higher
https://forum.qt.io/topic/36072/qmysql-driver-not-loaded-on-ubuntu/15
@JKSH said in An experiment to understand ways of copying C arrays to vector:
No resizing was done.
// using copy
vector<int> vec3;
qInfo() << vec3.capacity();
copy(arr, arr+arrsize, back_inserter(vec3));
loop("vec3", vec3);
Output:
0
vec3
10 16
std::vector(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
Maybe I said the wrong term. A reserve was done.
@Chris-Kawa said in connect is driving me batty!:
I sure would love to get rid of stuff like currentIndexChanged() overloaded on int and QString.
I failed with my last patch for it :D
@mrdebug said in A Makefile problem:
After having studying how to QtCreator generates a Makefile, I have inserted the following lines on code in my Makefile
Mmm, so are you editing the Makefile by hand?
I'm not sure it's a good way to go.
You may want to edit your Qt project file (.pro) and let qmake create your Makefile then, passing to it all your settings...
@fcarney said in How is this error possible? g++: error: build/.o: No such file or directory:
is what caused this.
is your issue solved then? If so please don't forget to mark your post as such. Thanks
@kshegunov I'm not an expert on that but I do see boost when optimizing for reduced vtable usage, so either my hardware doesn't do that good of a job or something else is going on. Thanks for a nudge, I guess it's something worth looking into.
Why not have a central where you collect the data and then have specific "propagetors" that will publish/send/whatever ?
You'll keep your devices focused on getting data and then you can an new propagation channels San you see fit.
@chrabaszcz-patryk
Hi I had the same problem with qtsqldrivers-config.pri
I leave it here, maybe it will be helpful
Go to :
/Qt_new/5.9.1/Src/qtbase/src/plugins/sqldrivers
Run qmake:
../../../../../gcc_64/bin/qmake sqldrivers.pro
After that I got:
Configure summary:
Qt Sql:
DB2 (IBM) .............................. no
InterBase .............................. no
MySql .................................. yes
OCI (Oracle) ........................... no
ODBC ................................... no
PostgreSQL ............................. no
SQLite2 ................................ no
SQLite ................................. yes
Using system provided SQLite ......... no
TDS (Sybase) ........................... no
Then go to:
/Qt_new/5.9.1/Src/qtbase/src/plugins/sqldrivers/mysql
Run qmake again:
../../../../../../gcc_64/bin/qmake mysql.pro
Run make:
make
You will see as a part of an output message that it was compiled and moved into:
"mv -f libqsqlmysql.so ../plugins/sqldrivers/"
I had this problem when added Qt 5.13.0 using online installation to the Qt 5.12 i have already installed i thought the installation was wrong until i came across your solution. Thanks you very much.
@aha_1980
Thank you for this tip.
This means I have to implement a timer with a interval of 200µs which kicks off reading of one new bit from the RX868SH-DV.
OK I will try it. And then I give you an answer.
But now I got a new problem using timers in QT-Creator. I make a new topic for this.
my new topic for two timer
@jjlee said in Can someone explain this syntax to me?:
the previous syntax doesn't seem to work anymore
It does, but you need to tell the compiler which version you want to use. For that you can use https://doc.qt.io/qt-5/qtglobal.html#qOverload macro.
One issue I ran into was my local variables were showing zeros as well. It wasn't until I inited the ram with 255 for every character and used new(mempool()) to use that preinited ram that I did see uninitialized ram. Of course that was on the heap and not the stack. I did test this over the weekend and observed what you said. Variables declared outside of local scope are initialized to zero. While stack and heap are not.
@fcarney
BTW, reading around (and then I must get back to my work!), it seems there is another C++ variant to int64_t(something) which is actually supposedly preferred (to just that one): int64_t{something}!
From what I read, the consensus is best to use the static_cast<> family of casts for all of this. The basic claim is that it makes it easier to search source code for these.
