Re: C++ Message Handling without using state machines

"Robbie Hatley" <bogus.address@no.spam>
Fri, 30 Jun 2006 09:37:42 GMT
"libster" <> wrote:

I'm writing code and I have a scenario where I'm waiting to receive
a msg and a timeout message at the same time.

That's a little superfluous, isn't it? I mean, a "timeout message"
already IS a "message". So what you really meant is, "I'm waiting
[callback function?] to receive messages, which may be timeout or

For example, I've set a timer so that if I don't receive a message
in a certain time, then I will receive a timeout message. Based on
which message I receive first I will perform certain tasks. Is
there a good way to handle this in C++ without using state machines?

I'd say a function which processes incoming messages and alters the
state of a system based on what messages it receives already IS a
"state machine". Why are you afraid of that term?

If I receive the timeout message first then what do I do when the
other message comes in or vice-versa? Need to determine a way to
find out, once I receive a message, if the other message has been
received yet. Any advice would be greatly appreciated.

Use static bool variables to keep track of whether certain messages
have been received yet by a function. Sort of like:

      HWND hWnd,
      UINT message,
      WPARAM wParam,
      LPARAM lParam
   static bool GotTimeout = false;
   static bool GotSleep = false;
   static bool GotWakeup = false;
   static bool GotExplode = false;
   switch (message)
      case TIMEOUT:
         GotTimeout = true;
         // do stuff
         return 1;
      case SLEEP:
         GotSleep = true;
         // do stuff
         return 1;
      case WAKEUP:
         GotWakeup = true;
         // do stuff
         return 1;
      case EXPLODE:
         return 666;
   return 0;

You'll have to decide under what conditions you want to reset
your "got-the-message" booleans so that they can be triggered
by the next message of that type. But I think the above scheme
would work.

Robbie Hatley
Tustin, CA, USA
lonewolfintj at pacbell dot net (put "[ciao]" in subject to bypass spam filter)

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