CODEWITHSUNDEEP
nullpowerbuilder
user1251698
user1251698

Reputation: 2143

PowerBuilder NULL and Empty variable

I'm using PowerBuilder and have a problem with the if condition. I want to check if a variable is not null or it is not empty.

So first I have following if condition to test if the variable is null or not:

IF IsNull(ls_name) THEN
    messagebox("ls_name", "is null")  //true
else
    messagebox("ls_name", "is not null")
end if

From the above condition, I know that ls_name is null. Now I test if its empty or not:

if ls_name = "" then
    messagebox ("ls_name", "is empty")
else
    messagebox("ls_name", "is not empty") //true
end if

And i get that ls_name is not empty.

Now when I use an if condition to check if ls_name is NOT Null or it is NOT empty, I put the following if condition:

IF not IsNull(ls_name) or ls_name <> "" THEN
    messagebox("test", "condition true")
else
    messagebox("test", "condition false")  //this becomes true.
end if

It goes to the else part of the condition. Shouldn't the if part become true? Am I writing the if condition wrong?

Upvotes: 0

Views: 33172

Answers (3)

Sid
Sid

Reputation: 765

Best technique i use for my programs are

If IsNull(ls_name) THEN ls_name = ""

IF Len(Trim(ls_name)) = 0 THEN

 ERR  MSG HERE

END IF

i always set null strings to empty spaces then check if the strings are empty.. it also depends on the scenario you are running

Upvotes: 0

Terry
Terry

Reputation: 6215

Thinking of "null" as "unknown" has always gotten me by in understanding how expressions evaluated.

So, when ls_name is null, 

not IsNull(ls_name) or ls_name <> ""

evaluates to

NOT TRUE OR UNKNOWN

or

FALSE OR UNKNOWN

Well, for an OR to evaluate to TRUE, at least one condition must be TRUE. That doesn't apply in this case.

The way I usually test for this is:

IF NOT (IsNull (ls_name) OR ls_name = "") THEN

which, when ls_name is null, resolves to

NOT (TRUE OR UNKNOWN)

then

NOT (TRUE)

and

FALSE

In other words, the variable is "empty".

Good luck,

Terry

Upvotes: 2

Seki
Seki

Reputation: 11465

Beware of PB manner for testing if conditions and null behavior:

  • unlike C language, PB is not making lazy evaluation, i.e it always evaluates all the parts of the condition and does not stop at the first false or true part
  • null is contagious, in the sense that if a part of a statement returns null, the whole statement becomes null
  • a null statement is always false when using if

So in your case, it is probable that when ls_name is null the not IsNull(ls_name)is evaluating to true, but ls_name <> "" is becoming null, thus true or null is becoming null and you always going to the else part.

I would check in 2 times :

if not IsNull(ls_name) then
    if ls_name <> "" then
        //not empty
    else
        //empty
    end if
else
    //null
end if

If you need to handle the same code for not empty / not null then you would have to use some kind of boolean flag. I also starting to use the goto statement that is handy when dealing with nested if statement.

(BTW : NO, goto- when used carefully - is not evil ;o)

Upvotes: 1

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