c++ - QT signal slot is not working -

i facing strange problem while trying execute following program

main.cpp

#include "sample.h" #include <qlist> #include <unistd.h>  int main(int argc, char **argv) {   a;   a.calla();   while(1)     sleep(1);   return 0; } 

sample.cpp

#include "sample.h" #include <qlist> #include <qmetamethod> #include <unistd.h>   thread::thread(a *a) { } void thread::run() {   int = 5;   while (i){     qdebug()<< i;     sleep(2);     i--;   }   emit processingdone(">>> thread");   qdebug()<<"emited signal thread"; }  void a::calla() {   qdebug()<<"from calla";   //movetothread(thread);   thread->start();   //thread->run();   //emit signala(">>> calla"); }  void a::slota(qstring arg) {   qdebug()<<"from sloata "<< arg; } 

sample.h

class a;     class thread : public qthread     {       q_object     public:       thread(a *a);       ~thread(){         qdebug()<<"thread destroyed";       }       void run();     signals:       void processingdone(qstring arg);     };      class : public qobject{     q_object      public:       a(){         qdebug()<<"registering";         thread = new thread(this);         connect(thread, signal(processingdone(qstring)), this, slot(slota(qstring)));         connect(this,signal(signala(qstring)), this, slot(slota(qstring)));       }     public slots:       void calla();       void slota(qstring arg);      signals:       void signala(qstring arg);      private:       thread *thread;     }; 

when try executed program, slot not getting invoked? if put movetothraed(), code work won't serve puprose. missing?

you not starting main event loop.

your main function should this:

qapplication app(argc, argv); a; a.calla(); return app.exec(); 

qt queued connections can't work if there no event loop running in receiving thread.

when receiver object lives in thread other thread signal emitted, qt::autoconnection uses qt::queuedconnection, see docs.

a qt::queuedconnection works posting event event loop of target thread (the thread receiver qobject lives). when event processed (by event loop) call slot invoked in target thread.

in case, main thread stuck in:

while(1)     sleep(1); 

so, never able execute else.