IsNull
PowerScript function
Description
Reports whether the value of a variable or expression is
null.
Syntax
|
1 |
IsNull ( any ) |
|
Argument |
Description |
|---|---|
|
any |
A variable or expression that you want to test to |
Return value
Boolean.
Returns true if any is null and false if it is not.
Usage
Use IsNull to test whether a user-entered value or a value retrieved
from the database is null.
If one or more columns in a DataWindow are required columns, that
is, they must contain data, you do not want to update the database if the
columns have null values. You can use FindRequired to find rows in which
those columns have null values, instead of using IsNull to evaluate each
row and column.
Setting a variable to null
To set a variable to null, use the SetNull function. In standard
PowerBuilder applications, if a variable is not set to null explicitly by
calling the SetNull function, calling the IsNull function against the
variable returns false.
If the variable is of a reference type (a type derived from the
PowerObject base class), IsNull returns true if the variable has not been
initialized by assigning an instantiated object to it. In the following
example, IsNull returns false in a standard PowerBuilder
application:
|
1 2 3 4 5 |
dataStore ds boolean b b = IsNull(ds) MessageBox("IsNull", string(b)) |
If the variable is explicitly set to null, IsNull returns true in
standard PowerBuilder applications:
|
1 2 3 |
SetNull(ds) b = IsNull(ds) MessageBox("IsNull", string(b)) |
Examples
These statements set lb_test to true:
|
1 2 3 4 5 |
integer a, b boolean lb_test SetNull(b) lb_test = IsNull(a + b) |
See also
IsNull method for DataWindows in the section called “IsNull” in DataWindow Reference.