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  • Safe Cross Thread Signals/Slot C++

    - by JP
    It seem that the only implementation that provide Safe Cross-Thread Signals for both the Signal class and what's being called in the slot is QT. (Maybe I'm wrong?). But I cannot use QT in the project I'm doing. So how could I provide safe Slots call from a different thread (Using Boost::signals2 for example)? Are mutex inside the slot the only way? I think signals2 protect themself but not what's being done inside the slot. Thanks

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  • Problem with signals and slots

    - by Jen
    I am creating a class with custom slots in Qt: class CustomEdit : public QTextEdit { Q_OBJECT public: CustomEdit(QWidget* parent); public slots: void onTextChanged (); }; However, I'm getting thise linker error: undefined reference to 'vtable for CustomEdit' The documentation says: if you get compiler errors along the lines of "undefined reference to vtable for LcdNumber", you have probably forgotten to run the moc or to include the moc output in the link command. ... but it is not obvious what that means. Is there something I need to add to my class, or to the .pro file?

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  • Functions connected to signals in QtScript (on Qt 4.5.2) are not firing

    - by Cody Brocious
    I've injected into a proprietary Qt (4.5.2) application, added my own compatible build of QtScript, and have managed to get access to all the signals I need. However, when connecting to them (via QtScript) my functions are never called. I've come up with a few theories for why this is and I've tested everything I can think of, but I've hit a bit of a wall. Note, I've never had any connection exceptions whatsoever. Here are my current theories: The signals I'm connecting to are already connected to other slots, and that's somehow blocking it (but as far as I know, all Qt signals fire to all slots with no extra work, and can't be restricted in this way) The signals are rejecting my connection, or disconnecting me after connection (but I see no facility for this) My connection is happening from another thread, and this is somehow causing it not to connect properly Are any of these theories plausible? If not, what have I missed?

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  • How to convert an existing callback interface to use boost signals & slots

    - by the_mandrill
    I've currently got a class that can notify a number of other objects via callbacks: class Callback { virtual NodulesChanged() =0; virtual TurkiesTwisted() =0; }; class Notifier { std::vector<Callback*> m_Callbacks; void AddCallback(Callback* cb) {m_Callbacks.push(cb); } ... void ChangeNodules() { for (iterator it=m_Callbacks.begin(); it!=m_Callbacks.end(); it++) { (*it)->NodulesChanged(); } } }; I'm considering changing this to use boost's signals and slots as it would be beneficial to reduce the likelihood of dangling pointers when the callee gets deleted, among other things. However, as it stands boost's signals seems more oriented towards dealing with function objects. What would be the best way of adapting my code to still use the callback interface but use signals and slots to deal with the connection and notification aspects?

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  • How does Qt implement signals and slots?

    - by anton
    Can someone explain to me the basic idea of Qt signals&slots mechanism IMPLEMENTATION? I want to know what all those Q_OBJECT macros do "in plain C++". This question is NOT about signals&slots usage. added: I know that Qt uses moc compiler to transform Qt-C++ in plain C++. But what does moc do? I tried to read "moc_filename.cpp" files but I have no idea what can something like this mean void *Widget::qt_metacast(const char *_clname) { if (!_clname) return 0; if (!strcmp(_clname, qt_meta_stringdata_Widget)) return static_cast<void*>(const_cast< Widget*>(this)); return QDialog::qt_metacast(_clname); } Thanks in Advance, anton

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  • POSIX threads and signals

    - by Donal Fellows
    I've been trying to understand the intricacies of how POSIX threads and POSIX signals interact. In particular, I'm interested in: What's the best way to control which thread a signal is delivered to (assuming it isn't fatal in the first place)? What is the best way to tell another thread (that might actually be busy) that the signal has arrived? (I already know that it's a bad idea to be using pthread condition variables from a signal handler.) For reference about why I want this, I'm researching how to convert the TclX package to support threads, or to split it up and at least make some useful parts support threads. Signals are one of those parts that is of particular interest.

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  • How to "signal" interested child processes (without signals)?

    - by Teddy
    I'm trying to find a good and simple method to signal child processes (created through SocketServer with ForkingMixIn) from the parent process. While Unix signals could be used, I want to avoid them since only children who are interested should receive the signal, and it would be overkill and complicated to require some kind of registration mechanism to identify to the parent process who is interested. (Please don't suggest threads, as this particular program won't work with threads, and thus has to use forks.)

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  • What exactly are signals and slots in Qt?

    - by Jen
    I know how they work conceptually, but how are signals and slots implemented in the Qt framework? Qt Creator treats them as keywords, but are they simply a set of macros, or is a special pre-processor required before these source files can be compiled? In other words, if I use Qt's signal/slot features in my code, can I easily compile it on any C++ compiler?

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  • Using PyQt signals correctly

    - by Skilldrick
    A while ago I did some work in Qt for C++; now I'm working with PyQt. I have a subclass of QStackedWidget, and inside that a subclass of QWidget. In the QWidget I want to click a button that goes to the next page of the QStackedWidget. My (simplified) approach is as follows: class Stacked(QtGui.QStackedWidget): def __init__(self, parent=None): QtGui.QStackedWidget.__init__(self, parent) self.widget1 = EventsPage() self.widget1.nextPage.connect(self.nextPage) self.widget2 = MyWidget() self.addWidget(self.widget1) self.addWidget(self.widget2) def nextPage(self): self.setCurrentIndex(self.currentIndex() + 1) class EventsPage(QtGui.QWidget): nextPage = QtCore.pyqtSignal() def __init__(self, parent=None): QtGui.QWidget.__init__(self, parent) self.continueButton = QtGui.QPushButton('Continue') self.continueButton.clicked.connect(self.nextPage) So, basically, I'm connecting the continueButton clicked signal to the EventsPage nextPage signal, which I'm then connecting in Stacked to the nextPage method. I could just delve into the internals of EventsPage in Stacked and connect self.widget1.continueButton.clicked, but that seemed to completely defeat the purpose of signals and slots. So does this approach make sense, or is there a better way?

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  • Qt QNetworkAccessManager does not emit signals

    - by Emilio
    The function CheckSite() is called with an url like http://site.com, it initializes a QNetworkAccessManager object and connect() slots and signals. The manger-get() call seems work (it generates http traffic) but does not call the slot replyFinished() at the request end. What's wrong with this code? #include <QtCore> #include <QtNetwork> class ClientHandler : public QObject { Q_OBJECT QNetworkAccessManager *manager; private slots: void replyFinished(QNetworkReply *); public: void CheckSite(QString url); }; void ClientHandler::replyFinished(QNetworkReply *reply) { qDebug() << "DONE"; } void ClientHandler::CheckSite(QString url) { QUrl qrl(url); manager = new QNetworkAccessManager(this); connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(replyFinished(QNetworkReply*))); manager->get(QNetworkRequest(qrl)); }

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  • Determine signals connected to a given slot in Qt

    - by Cody Brocious
    I've injected myself into a Qt application, and I'm attempting to figure out what signals a given slot is connected to, but can't find any information on doing this. Is there a mechanism for doing this out of the box? If so, is this exposed to QtScript? (If not, I can wrap it easily enough.) If there is no such mechanism, what would be the best way to add it? I cannot manipulate the existing application outside of simple hooking, but I could hook QObject::connect and store the connections myself, just not sure if that's the best way to go about it.

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  • Qt C++ signals and slots did not fire

    - by Xegara
    I have programmed Qt a couple of times already and I really like the signals and slots feature. But now, I guess I'm having a problem when a signal is emitted from one thread, the corresponding slot from another thread is not fired. The connection was made in the main program. This is also my first time to use Qt for ROS which uses CMake. The signal fired by the QThread triggered their corresponding slots but the emitted signal of my class UserInput did not trigger the slot in tflistener where it supposed to. I have tried everything I can. Any help? The code is provided below. Main.cpp #include <QCoreApplication> #include <QThread> #include "userinput.h" #include "tfcompleter.h" int main(int argc, char** argv) { QCoreApplication app(argc, argv); QThread *thread1 = new QThread(); QThread *thread2 = new QThread(); UserInput *input1 = new UserInput(); TfCompleter *completer = new TfCompleter(); QObject::connect(input1, SIGNAL(togglePause2()), completer, SLOT(toggle())); QObject::connect(thread1, SIGNAL(started()), completer, SLOT(startCounting())); QObject::connect(thread2, SIGNAL(started()), input1, SLOT(start())); completer->moveToThread(thread1); input1->moveToThread(thread2); thread1->start(); thread2->start(); app.exec(); return 0; } What I want to do is.. There are two seperate threads. One thread is for the user input. When the user enters [space], the thread emits a signal to toggle the boolean member field of the other thread. The other thread 's task is to just continue its process if the user wants it to run, otherwise, the user does not want it to run. I wanted to grant the user to toggle the processing anytime that he wants, that's why I decided to bring them into seperate threads. The following codes are the tflistener and userinput. tfcompleter.h #ifndef TFCOMPLETER_H #define TFCOMPLETER_H #include <QObject> #include <QtCore> class TfCompleter : public QObject { Q_OBJECT private: bool isCount; public Q_SLOTS: void toggle(); void startCounting(); }; #endif tflistener.cpp #include "tfcompleter.h" #include <iostream> void TfCompleter::startCounting() { static uint i = 0; while(true) { if(isCount) std::cout << i++ << std::endl; } } void TfCompleter::toggle() { // isCount = ~isCount; std::cout << "isCount " << std::endl; } UserInput.h #ifndef USERINPUT_H #define USERINPUT_H #include <QObject> #include <QtCore> class UserInput : public QObject { Q_OBJECT public Q_SLOTS: void start(); // Waits for the keypress from the user and emits the corresponding signal. public: Q_SIGNALS: void togglePause2(); }; #endif UserInput.cpp #include "userinput.h" #include <iostream> #include <cstdio> // Implementation of getch #include <termios.h> #include <unistd.h> /* reads from keypress, doesn't echo */ int getch(void) { struct termios oldattr, newattr; int ch; tcgetattr( STDIN_FILENO, &oldattr ); newattr = oldattr; newattr.c_lflag &= ~( ICANON | ECHO ); tcsetattr( STDIN_FILENO, TCSANOW, &newattr ); ch = getchar(); tcsetattr( STDIN_FILENO, TCSANOW, &oldattr ); return ch; } void UserInput::start() { char c = 0; while (true) { c = getch(); if (c == ' ') { Q_EMIT togglePause2(); std::cout << "SPACE" << std::endl; } c = 0; } } Here is the CMakeLists.txt. I just placed it here also since I don't know maybe the CMake has also a factor here. CMakeLists.txt ############################################################################## # CMake ############################################################################## cmake_minimum_required(VERSION 2.4.6) ############################################################################## # Ros Initialisation ############################################################################## include($ENV{ROS_ROOT}/core/rosbuild/rosbuild.cmake) rosbuild_init() set(CMAKE_AUTOMOC ON) #set the default path for built executables to the "bin" directory set(EXECUTABLE_OUTPUT_PATH ${PROJECT_SOURCE_DIR}/bin) #set the default path for built libraries to the "lib" directory set(LIBRARY_OUTPUT_PATH ${PROJECT_SOURCE_DIR}/lib) # Set the build type. Options are: # Coverage : w/ debug symbols, w/o optimization, w/ code-coverage # Debug : w/ debug symbols, w/o optimization # Release : w/o debug symbols, w/ optimization # RelWithDebInfo : w/ debug symbols, w/ optimization # MinSizeRel : w/o debug symbols, w/ optimization, stripped binaries #set(ROS_BUILD_TYPE Debug) ############################################################################## # Qt Environment ############################################################################## # Could use this, but qt-ros would need an updated deb, instead we'll move to catkin # rosbuild_include(qt_build qt-ros) rosbuild_find_ros_package(qt_build) include(${qt_build_PACKAGE_PATH}/qt-ros.cmake) rosbuild_prepare_qt4(QtCore) # Add the appropriate components to the component list here ADD_DEFINITIONS(-DQT_NO_KEYWORDS) ############################################################################## # Sections ############################################################################## #file(GLOB QT_FORMS RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} ui/*.ui) #file(GLOB QT_RESOURCES RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} resources/*.qrc) file(GLOB_RECURSE QT_MOC RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} FOLLOW_SYMLINKS include/rgbdslam_client/*.hpp) #QT4_ADD_RESOURCES(QT_RESOURCES_CPP ${QT_RESOURCES}) #QT4_WRAP_UI(QT_FORMS_HPP ${QT_FORMS}) QT4_WRAP_CPP(QT_MOC_HPP ${QT_MOC}) ############################################################################## # Sources ############################################################################## file(GLOB_RECURSE QT_SOURCES RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} FOLLOW_SYMLINKS src/*.cpp) ############################################################################## # Binaries ############################################################################## rosbuild_add_executable(rgbdslam_client ${QT_SOURCES} ${QT_MOC_HPP}) #rosbuild_add_executable(rgbdslam_client ${QT_SOURCES} ${QT_RESOURCES_CPP} ${QT_FORMS_HPP} ${QT_MOC_HPP}) target_link_libraries(rgbdslam_client ${QT_LIBRARIES})

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  • Scanf with Signals

    - by jreid42
    I have a signal that blocks SIGINT and basically says "Sorry, you can't quit.\n" The issue is this can occur during a scanf. When this occurs during a scanf, scanf takes in the printf as input. How can I do a printf that will cause scanf to basically hit the enter key automatically. I don't care that I am getting bad input. I just want to programatically finish that scanf with a printf or something else. Process: scanf("get stuff") - User is able to enter stuff in. - SIGINT occurs and goes to my handler. - Handler says "Blah blah blah" to stdout. - Scanf has taken this blah blah blah and is waiting for more input. How do I make it so that when I return scanf is finished (don't care what it has gathered I just want it to continue without user help).

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  • C signals and processes

    - by Gary
    Hi, so basically I want "cmd_limit" to take a number in seconds which is the maximum time we'll wait for the child process (safe to assume there's only one) to finish. If the child process does finish during the sleep, I want cmd_limit to return pass and not run the rest of the cmd_limit code. Could anyone help me do this, here's what I've got so far.. int cmd_limit( int limit, int pid ) { signal( SIGCHLD, child_died ); sleep( limit ); kill( pid, SIGKILL ); printf("killin'\n"); return PASS; } void child_died( int sig ) { int stat_loc; /* child return information */ int status; /* child return status */ waitpid( -1, &stat_loc, WNOHANG ); if( WIFEXITED(stat_loc) ) { // program exited normally status = WEXITSTATUS( stat_loc ); /* get child exit status */ } printf("child died: %s\n", signal); }

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  • Boost signals and passing class method

    - by Ockonal
    Hello, I've defined some signal: typedef boost::signals2::signal<void (int temp)> SomeSig; typedef SomeSig::slot_type SomeSigType; I have some class: class SomeClass { SomeClass() { SomeSig.connect(&SomeClass::doMethod); } void doMethod(const SomeSig &slot); }; And got a lot of errors: error: ‘BOOST_PP_ENUM_SHIFTED_PARAMS_M’ was not declared in this scope error: ‘T’ was not declared in this scope error: a function call cannot appear in a constant-expression error: a function call cannot appear in a constant-expression error: template argument 1 is invalid error: ‘BOOST_SIGNALS2_MISC_STATEMENT’ has not been declared error: expected identifier before ‘~’ token error: expected ‘)’ before ‘~’ token error: expected ‘;’ before ‘~’ token

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  • How to process signals in a Qt subclass?

    - by Jen
    How do I process a signal of in a subclass? Let's say my subclass is derived from QTextEdit and is interested in the signal textChanged. It seems silly to connect an object to itself, I should be able to simply override the textChange method -- but it isn't virtual. What is the accepted way to do this?

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  • Evaluating and Investigating Drug Safety Signals with Public Databases Webinar

    - by Roxana Babiciu
    In this one-hour webinar, BioPharm Systems' Dr. Rodney Lemery, vice president of safety and pharmacovigilance, will review a number of public databases available to use during the evaluation and investigation of identified safety signals. The discussion will focus on the use of free and paid longitudinal healthcare databases available online. After attending this presentation, you will better understand how these data sources can be used in your daily PV work. Read more here

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  • What is the correct Qt idiom for exposing signals/slots of contained widgets?

    - by Tyler McHenry
    Suppose I have a MyWidget which contains a MySubWidget, e.g. a custom widget that contains a text field or something. I want other classes to be able to connect to signals and slots exposed by the contained MySubWidget instance. Is the conventional way to do this: Expose a pointer to the MySubWidget instance through a subWidget() method in MyWidget Duplicate the signals and slots of MySubWidget in the MyWidget class and write "forwarding" code Something else? Choice 1 seems like the least code, but it also sort of breaks encapsulation, since now other classes know what the contained widgets of MyWidget are and might become dependent on their functionality. Choice 2 seems like it keeps encapsulation, but it's a lot of seemingly redundant and potentially convoluted code that kind of messes up the elegance of the whole signals and slots system. What is normally done in this situation?

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  • Less is more: The making of a 37 signals style pizza

    - by Liam McLennan
    For years now we have been hearing from 37 signals that the way to bake a great web app is to build less – well the same is true of pizza. Our western hedonism has led us to pursue ever cheesier and more stuffed crusts at the expense of the simple flavours. All we are left with is a fatty, salty heart attack in waiting. The Italians know that the secret to great taste is simplicity. With that in mind I decided to base my pizza masterpiece on these simple flavours: tomato sopressa (spicy aged salami) mozzarella garlic basil Of course the first thing one needs when making pizza is a base.   A freshly made base is extremely important but unfortunately I was too lazy. Next up is the tomato sauce. My wife made the sauce by reducing some tomatoes and adding herbs and sugar. We had selected some fine ingredients to make our topping: sopressa salami, fresh basil and the best mozzarella we could find.   It is, according to google, important to bake pizza at a high temperature, so I set the oven to 250C (480F). Here are the before and after shots: Meanwhile, the dog did nothing.

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  • How to properly handle signals when using the worker thread pattern?

    - by ipartola
    I have a simple server that looks something like this: void *run_thread(void *arg) { // Communicate via a blocking socket } int main() { // Initialization happens here... // Main event loop while (1) { new_client = accept(socket, ...); pthread_create(&thread, NULL, &run_thread, *thread_data*); pthread_detach(thread); } // Do cleanup stuff: close(socket); // Wait for existing threads to finish exit(0); ) Thus when a SIGINT or SIGTERM is received I need to break out of the main event loop to get to the clean up code. Moreover most likely the master thread is waiting on the accept() call so it's not able to check some other variable to see if it should break;. Most of the advice I found was along the lines of this: http://devcry.blogspot.com/2009/05/pthreads-and-unix-signals.html (creating a special signal handling thread to catch all the signals and do processing on those). However, it's the processing portion that I can't really wrap my head around: how can I possibly tell the main thread to return from the accept() call and check on an external variable to see if it should break;?

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  • DIY Weather-Aware Umbrella Stand Signals Stormy Weather

    - by Jason Fitzpatrick
    This clever DIY project adds ambient weather notification to your umbrella stand–simply walk by it on your way out the door to get a subtle reminder to take your umbrella. The clever setup involves a hobby board, motion detection, and LEDS to a rather clever end. As you walk by the semi-translucent umbrella stand all of it is mounted in, it lights up to indicate the weather conditions. Blue indicates the forecast for the day shows no sign of rain, green indicates rain, and red indicates thunderstorms. Check out the above video to see the hardware involves and the stand in action; hit up the link below for the full build guide including code. DIY Umbrella Stand Hack with Rain Alert [via Make] How To Delete, Move, or Rename Locked Files in Windows HTG Explains: Why Screen Savers Are No Longer Necessary 6 Ways Windows 8 Is More Secure Than Windows 7

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  • Can I use POSIX signals in my Perl program to create event-driven programming?

    - by Shiftbit
    Is there any POSIX signals that I could utilize in my Perl program to create event-driven programming? Currently, I have multi-process program that is able to cross communicate but my parent thread is only able to listen to listen at one child at a time. foreach (@proc) { sysread(${$_}{'read'}, my $line, 100); #problem here chomp($line); print "Parent hears: $line\n"; } The problem is that the parent sits in a continual wait state until it receives it a signal from the first child before it can continue on. I am relying on 'pipe' for my intercommunication. My current solution is very similar to: http://stackoverflow.com/questions/2558098/how-can-i-use-pipe-to-facilitate-interprocess-communication-in-perl If possible I would like to rely on a $SIG{...} event or any non-CPAN solution. Update: As Jonathan Leffler mentioned, kill can be used to send a signal: kill USR1 = $$; # send myself a SIGUSR1 My solution will be to send a USR1 signal to my child process. This event tells the parent to listen to the particular child. child: kill USR1 => $parentPID if($customEvent); syswrite($parentPipe, $msg, $buffer); #select $parentPipe; print $parentPipe $msg; parent: $SIG{USR1} = { #get child pid? sysread($array[$pid]{'childPipe'}, $msg, $buffer); }; But how do I get my the source/child pid that signaled the parent? Have the child Identify itself in its message. What happens if two children signal USR1 at the same time?

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