LrealIsNaN

This function tests whether a value is NaN (Not a Number). If the return value is TRUE, the value is NaN.

Return value

Name	Type	Description
LrealIsNaN	BOOL	If the return value is TRUE, the value is NaN.

VAR_INPUT
    x        : REFERENCE TO LREAL;
END_VAR

Name	Type	Description
x	REFERENCE TO LREAL	Transfers the value being tested.

The following points rank among the main features of NaN values:

All arithmetic operations that use NaN as input data return NaN as the result.
All relational operators =, !=, > < >= <= always return the value False if at least one of the operands is NaN.
The standard C functions isnan() or _isnan() or the PLC functions LrealIsNaN() and RealIsNaN (Tc2_Utilities library) return the value True if the argument has the value NaN.
The expression isnan(a) is equivalent to the expression !(a == a) or NOT(a = a).

The fact that NaN values reproduce themselves when used in further calculations is advantageous in that invalid values cannot be overlooked.

CAUTION

Software malfunctions

NaN values can lead to potentially dangerous malfunctions of the software concerned!

Only use expressly approved NaN values, specifically as control values in motion control and drive control functions.

Notice

Machine damage due to floating point exceptions (FP exceptions)

Comparisons with NaN values can lead to an exception, which result in the runtime stopping and potentially machine damage.

Switch off the FP exceptions if NaN values are to be used and processed in the application.

Development environment	Target platform	PLC libraries to be integrated (category group)
TwinCAT v3.1.4020	PC or CX (x86, x64, Arm^®)	Tc2_Utilities (System) >=3.3.16.0