Degging Windows Programs

[Joe Speroni]

I declared a GLOBAL value for debbuging in my windows
progam

GLOBAL alertvalue AS STRING

then defined a Callback function

CALLBACK FUNCTION Alert()
alertvalue="Hello"
END FUNCTION

and called the function from dialog button CALL.

Then in the "main loop" for my dialog (just after the
FUNCTION=action statement), I put the statements

IF alertvalue>"" THEN MSGBOX alertvalue:alertvalue=""
=====================================================

I never get a MSGBOX. Why isn't alertvalue being
set, and the MSGBOX showing its value?

Is there another smarter way to display values seen
inside CALLBACK functions?

[Matthew Berg]

If you are testing alertvalue to see if it has a value, why do you use the comparison operator ">"? Should that not be IF alertvalue <> "" THEN ...

[Joe Speroni]

I appreciate your taking the time to answer, but all strings are greater
than the null string. That's not it, but I did change the code anyway.
(just in case). No my problem has some other origin.

[Chris Boss]

Joe:

>Then in the "main loop" for my dialog (just after the
>FUNCTION=action statement), I put the statements
>
>IF alertvalue>"" THEN MSGBOX alertvalue:alertvalue=""

The first NO, NO is "Never" try to display a messagebox from within a DialogBox (or window Proc) Procedure unless it is done when a specific message is processed (like WM_COMMAND).

By putting the messagebox command in a place where it can be executed by any Dialog Message (ie, where you put it), you may be trying to display a messagebox during a particular message that Windows finds offensive.

Do NOT assume that a Dialog Procedure is dormant. There are a bunch of messages that are processed before a Window (Dialog) is even displayed, ie. WM_NCCREATE, WM_INITDIALOG and possibly others.

By putting the messagebox command in a place that where it may execute during a windows message that does not like it, you can cause problems, even GPFs.

If you move your messagebox command to the WM_COMMAND message and test for say a Button press and then execute it, it should work fine.