FLTK Fl_Choice obtain selected item - visual-c++

Question

I want to get the selected item of users but it gives an error on this code:
choice->value();
hopes you kind guys can help me.
Fl_Choice* choice;
int i = 0;
void but_cb(Fl_Button* obj, void*)
{
i = choice->value();
cout<<i;
}
int main (int argc, char* argv[]) {
Fl_Double_Window* win = new Fl_Double_Window(400,400,"Sample");
win->begin();
Fl_Choice* choice = new Fl_Choice(100,100,100,100,"Name");
choice->add("Peter");
choice->add("Tom");
choice->add("Mary");
Fl_Button* but = new Fl_Button(300,300,50,50,"Selected");
but->callback((Fl_Callback*)but_cb);
win->show();
return (Fl::run());
}

Answer 1

I did not spend much time reading the code, so the modified, and commented code below may not be solution to your problem. I believe choice is NULL in but_cb() as you are redefining choice in your main() function, hiding the global 'choice' pointer.
Fl_Choice* choice;
int i = 0;
void but_cb(Fl_Button* obj, void*) {
i = choice->value(); // uses global `choice` pointer to Fl_Choice.
cout << i;
}
int main (int argc, char* argv[]) {
Fl_Double_Window* win = new Fl_Double_Window(400,400,"Sample");
win->begin();
/* You are redefining choice here! BAD, because but_cb uses the global one.
Fl_Choice* choice = new Fl_Choice(100,100,100,100,"Name");
*/
// Good, assigns to the global `choice`, so it won't be NULL when but_cb is called
choice = new Fl_Choice(100,100,100,100,"Name");
choice->add("Peter");
choice->add("Tom");
choice->add("Mary");
Fl_Button* but = new Fl_Button(300,300,50,50,"Selected");
but->callback((Fl_Callback*)but_cb);
win->show();
return (Fl::run());
}