emitting and catching signals

[nish]

connect(classA_object,SIGNAL(receiving_finished()), classB_object, SLOT(write_data()));
//This is present in the mainclass's constructor which has a instance of classB_object but no classA instance.

connect(classA_object,SIGNAL(receiving_finished()), classB_object, SLOT(write_data()));
//This is present in the mainclass's constructor which has a instance of classB_object but no classA instance.

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you say the "no classA instance." is present in mainclass so how are you able to connect..
i am afraid that you need to give some more code... why not just provide a simple minimal compilable program reproducing the problem?

[srohit24]

Should i place the connect command in classB's constructor to connect the signals as classB has classA's instance?

EDIT

I placed the connect code in the classB's constructor.The app compiled successfully but i got this in qDebug

connect(classA_object,SIGNAL(receiving_finished()), this, SLOT(write_data()));
 
QObject::connect: Cannot connect (null)::receiving_finished() to classB::write_data()

connect(classA_object,SIGNAL(receiving_finished()), this, SLOT(write_data()));

QObject::connect: Cannot connect (null)::receiving_finished() to classB::write_data()

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[spirit]

classA_object is not created, i.e. classA_object == 0.
EDIT: take a debugger in your hands and debug your programm step by step.

[srohit24]

ok. but I have created a class object and I am using it make a function call.

how can that be null?

[spirit]

this message says another

QObject::connect: Cannot connect (null)::receiving_finished() to classB::write_data()