Search code examples
functionsyntaxnullpowerbuilder

PowerBuilder: when argument to a function is in dot-notation and has value null, a null is NOT received

I am calling a user-defined function and passing an argument that is in dot notation. For example,

of_testingnullarg( tab_2.tabpage_comp_info.dw_webcomp_info.object.dormant[i] )

The above function is purely to demonstrate this problem. It accepts a long parameter and uses isNull() and messagebox() to tell the user if the parameter is null or not. Here is its listing:

// of_testingnullarg( al_arg1 )
// strictly an experiment

if isNull(al_arg1) then
    messageBox("al_arg1", "is null inside of_testingNullArg")
else
    messageBox("al_arg1", "is NOT null inside of_testingNullArg, it is "+string(al_arg1))
end if

When the dormant[i] (referring to the first function call) control contains a number, there is no problem--the parameter inside of_testingnullarg will contain the same number, as expected. But when the dormant[i] control has read null from the database, I find that the parameter inside of_testingnullarg does NOT hold null. It holds a number such as 16. Null was passed in (according to isNull()), but the parameter inside of_testingnullarg holds a number. It is not a random number, it is consistent, but seems to be dependent on how many parameters the function accepts.

This problem does NOT reveal itself when I run the program inside the Powerbuilder IDE. (I am running Powerbuilder 12.5) It shows up only when I build the program and run the executable.

I have found that if I first do this, the problem goes away:

long ll_dormant
ll_dormant = tab_2.tabpage_comp_info.dw_webcomp_info.object.dormant[i]
of_testingnullarg( ll_dormant )

To summarize, the problem shows up when 3 things are true:

  1. I am NOT running the program through the Powerbuilder IDE
  2. My argument is in dot-notation (not inside a variable)
  3. The value in the control is null

I think this must have something to do with a pointer on the call stack. It must be off 2 bytes or something. Is it common knowledge to always put the value into a variable first?

Solution

  • I have found out that dot-notation returns type 'ANY'. This is a problem when the value is NULL which is typeless. PowerBuilder is trying to do an implicit cast of a NULL Any value to a NULL Long and gets confused. The solution is to help PowerBuilder with the type BEFORE the function call (which is why putting it into a variable first worked). These also work:

    of_testingnullarg( LONG(tab_2.tabpage_comp_info.dw_webcomp_info.object.dormant[i]) )

    or

    of_testingnullarg( tab_2.tabpage_comp_info.dw_webcomp_info.GetItemNumber(i, "dormant") )