How to use PostMessage from standard c++ function to MFC dialog?

Question

I created aaa.cpp and aaaDlg.cpp and I want to update dialog GUI from aaa function to Dialog function.

How to use PostMessage from standard c++ function to MFC dialog?
Any examples is better.

============================ Standard c++
aaa.cpp
void AAA::function()
{
PostMessage (........)
}

//===========================MFC
aaaDlg.cpp

include "stdafx.h"

void GetAAADlg::UpdateUI()
{

}