Question

I am creating a VCL forms application with multiple forms. I have created a new form called formCreateAppointment.

I am trying to load the form via this code in a menuItem:

formCreateAppointment.Show();

I am getting this error:

E2451 Undefined symbol ‘formCreateAppointment’

Do I have to declare this form as a ‘global’ object or something similiar?

Thanks

More Info

The form ‘formCreateAppointment’ is under the Project->Options->Auto-create forms. When I use the code:

formCreateAppointment->Show();

My code will not compile and I get the following error:

E2451 Undefined symbol ‘formCreateAppointment’

Answer 1

When you create a new Form class in the IDE, the generated .hpp file contains a global pointer for you, eg:

#ifndef Unit2H
#define Unit2H

#include <Classes.hpp>
//...

class TformCreateAppointment : public TForm
{
    //...
}; 

extern PACKAGE TformCreateAppointment *formCreateAppointment; // <-- here

#endif

It sounds like you have not #include‘d that .hpp file into your main code, eg:

#include "Unit2.hpp" // (or whatever you decided to name that Form's unit as)

If you set that Form to be Auto-Created in the Project Options, that global pointer will be automatically instantiated at program startup for you (by inserting a call to Application->CreateForm() in your project’s WinMain() function). Otherwise, you have to instantiate it manually in your code using the new operator instead.

Either way, the variable is a pointer. VCL objects cannot be instantiated on the stack, only the heap. You have to use the -> operator to access members of the Form object, eg:

formCreateAppointment->Show(); 

If you want to use the . operator instead then you have to dereference the pointer first:

(*formCreateAppointment).Show();