Description
You can use the instruction "Check for UNEQUALS NULL pointer" to query whether the VARIANT or the reference does not point to a NULL pointer and therefore points to an object.
The <operand> must have the data type VARIANT or REF_TO <data type>.
|
Note VARIANT tag points to an ANY pointer If the VARIANT tag points to an ANY pointer, the instruction always returns the result RLO = "1" even if the ANY pointer is NULL. |
Parameters
The following table shows the parameters of the "Check for UNEQUALS NULL pointer" instruction:
|
Parameters |
Declaration |
Data type |
Memory area |
Description |
|---|---|---|---|---|
|
<operand> |
Input |
VARIANT or REF_TO <data type> |
L (The declaration is possible in the "Input", "InOut" and "Temp" sections of the block interface.) |
Operand that is compared for UNEQUALS NULL |
|
OUT |
Output |
BOOL |
I, Q, M, D, L |
Result of comparison |
For additional information on valid data types, refer to "See also".
Example
The following example shows how the instruction works:
The "TagOut" output is set when the following conditions are fulfilled:
-
The operands "Tag_In1" and "Tag_In2" have signal state "1".
-
The condition of the comparison instruction is fulfilled, i.e. the #Tag_Operand operand points to an object.