Thread: Custom Windows Message.

Hi. im trying to get messages from one application to the next. The two apps are not sharing any resources and are totally independant. So, I decided to use the windows message pump to pass messages back and forth. Can anyone provide me wih some info about this topic because I apperently I cannot find any

The messages are going to be custom made, so they dont interfere with the windows messages that get passed around.

Well in order to use custom messages, they need to be defined as a value greater than WM_USER. So, if I wanted a message like WM_MYMESSAGE:-

Code:

#define WM_MYMESSAGE    (WM_USER + 1)

The only problem is: what's stopping another program from doing the same thing for its own messages?
The answer: RegisterWindowMessage.

Code:

unsigned int uiMessage;

uiMessage = RegisterWindowMessage("WM_MYMESSAGE");

The return value of RegisterWindowMessage is guaranteed to be unique across the entire system and within the range WM_USER to 0x7FFF. As many applications that use the message may call RegisterWindowMessage, they will all get the same value to use.

So, you've done all that, now what about passing stuff? Passing an integer here and there is easily done, wParam and lParam are at your disposal...

Code:

LRESULT WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
   switch (uMsg)
   {
      ...
      case WM_MYMESSAGE:
      {
         if (wParam == 1)
            MessageBox(hwnd, "Woot!", "Hello!", MB_ICONEXCLAMATION);

         break;
      }

   }

   return FALSE;
}

BUT... what if you want to pass a string, or a pointer to a structure? Then things get tougher. The thing is, each process's memory is protected from other processes. They can't just pop inside each other's address space and compare notes. What you need is, specifically for messaging, some shared memory. This is known as custom marshalling.

And it's not something I know how to do.

Consider proxy.

WM_COPYDATA

Kuphryn

Ok Thnx for the help. Tho i do have more questions, How would i get the hWnd of a registered window, is there a lookup function?

Originally Posted by Mastadex

Ok Thnx for the help. Tho i do have more questions, How would i get the hWnd of a registered window, is there a lookup function?

FindWindow

Code:

unsigned int uiMessage;

uiMessage = RegisterWindowMessage("WM_MYMESSAGE");

...

LRESULT WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
   switch (uMsg)
   {
      ...
      case WM_MYMESSAGE:
      {
         if (wParam == 1)
            MessageBox(hwnd, "Woot!", "Hello!", MB_ICONEXCLAMATION);

         break;
      }

   }

   return FALSE;
}

I was wondering how you would know what WM_MYMESSAGE would be in the WndProc. Would you have to make it a global and then like case uiMessage?