Signal and slot Qt - c++

Question

I’m trying to write a very simple calendar program (I’m trying to learn Qt). The program itself is very basic, all it does is open a dialog box which displays today’s date with a button next to it. When the button is pressed another dialog opens, which I’ll call the calendar picker.
Here is the gist of the program: First, the main dialog opens with the current date. Then when the button shown in the picture is pushed, a signal is sent to a function which opens the picker and sets up a connection between the two classes which I'll describe below! The picker opens in which you can choose a date if you want. Let's say you choose a date by double clicking it. A signal is then sent to a function which closes the picker and the function then emits a signal to the main dialog to update the date to the new date. Now here's the problem:
Both the main dialog and the picker are in separate classes and I'm trying to set up a connection between the two classes when an item is double clicked.
***EDIT: Ok, now my problem is that I have Picker *mypicker declared in my header file and when I try using it in the .cpp file for example mypicker->show(); it causes the program to crash. Anyone know why?
Any help would be appreciated!!

Answer 1

undefined reference to MainDialog::updateDate(QDate)
Usually means that the compiler or the linker can't find the reference to it. So in your header, you make a promise that it will exist.
Then if when matching things up later the reference was never found... you get an error.
So what probably happened is one of a few things:
In your maindialog.cpp file you have:
// Either no definition of updateDate at all, Wrong because you put in your header a declaration for one.
void updateDate(QDate date) // Wrong because it doesn't specify MainDialog
{
}
void MainDialog::updateDate() // Wrong because it doesn't match the parameter list
{
}
void MainDialog::updatedate(QDate date) // Wrong because the function name is off
{
}
QDate MainDialog::updateDate(QDate date) // Wrong because return type is off
{
}
void MainDialog::updateDate(QDate date) // Correct! Matches the header file perfectly!
{
}
Then after you get past that, and other compile errors, keep an eye on the Application Output, because the connect call is a runtime connection, so it won't report a syntax mis-alignment until at the moment a connection is attempted.
Hope that helps.