Question

If I have a C++/CLI form with textbox1 and a class called Dummy in another header file, what can I do if I want to change “directly” the value of textbox1.Text by a function exists in Dummy class?

Answer 1

C++ does single-pass compilation. That means you can’t use something until the compiler has already seen it.

When you have two classes using each other mutually, that can be tricky. Luckily C++ also allows forward declaration, which tells the compiler “Here is the signature for a class or function I’m going to provide you with later”.

In general, provide the compiler with the following, in this order:

• forward declaration of classes

  ref class Dummy;
  ref class MyForm;
  

• class definitions

  ref class Dummy { ... };
  ref class MyForm { ... };
  

• class member function definitions

  void Dummy::DoIt()
  {
      myForm->textBox1->Text = whatever;
  }
  

Often, the only thing needed is to put function definitions in a .cpp file, and make sure that .cpp file #includes the header file for every class. For your problem, that’d mean you should put this line in Dummy.cpp, which includes both Dummy.h and myform.h.