Pragmas

A pragma is a { … } annotation that attaches metadata to a declaration without changing its data type. logiccloud supports two kinds: the access pragma on variable declarations and the JSON pragma on struct elements.

Access pragma

The access pragma is written after a variable declaration and controls how that variable is exposed to connectors and the HMI, and how it behaves on reset.

VAR
    speed   : REAL { IN HMI };
    state   : INT  { OUT RESET_TO 0 };
    setpoint: REAL { IN_OUT INTERNAL };
END_VAR

Keywords

Keyword	Meaning
IN	Expose the variable as an input access variable.
OUT	Expose the variable as an output access variable.
IN_OUT	Expose as both input and output (two access variables generated).
HMI	Make the access variable visible in the HMI.
INTERNAL	Mark as internal use only (not used in connectors; typically HMI-only values).
RESET_TO <const>	On program reset, reset the variable to a constant value.
NO_RESET	Do not reset the variable on program reset.
RESET_DEFAULT	Reset the variable to its default value on program reset (the default policy).

A pragma names one direction (IN, OUT or IN_OUT), optionally INTERNAL and/or HMI, and — for OUT / IN_OUT — an optional reset policy. The reset keywords are mutually exclusive.

VAR
    sensor : BOOL { IN HMI };                 // HMI-visible input
    alarm  : BOOL { OUT HMI NO_RESET };       // retained across resets
    gain   : REAL { OUT RESET_TO 1.0 };       // reset to 1.0
    scratch: INT  { OUT INTERNAL };           // internal, not a connector
END_VAR

Note

The access pragma is the code-level equivalent of the input/output configuration described in Project Elements → Inputs & Outputs, which covers the generated access-variable names, the HMI implications and the IN_OUT two-variable behavior in detail. Refer to that page for the full workflow; this page documents only the ST syntax.

JSON struct-element pragma

A struct element can carry a { JSON … } pragma that controls how that element is serialized to / deserialized from JSON.

TYPE
    Reading : STRUCT
        id        : DINT;
        value     : REAL  { JSON "measurement" };   // rename the JSON field
        debugInfo : STRING { JSON IGNORE };          // omit from JSON entirely
        note      : STRING { JSON OMIT_EMPTY };      // drop when empty
        label     : STRING { JSON "tag" OMIT_EMPTY };// rename and omit when empty
    END_STRUCT;
END_TYPE

Options

Form	Effect
{ JSON IGNORE }	The element is excluded from JSON serialization.
{ JSON "name" }	Use "name" as the JSON field name instead of the element name.
{ JSON OMIT_EMPTY }	Omit the element from the JSON output when it holds an empty/zero value.
{ JSON "name" OMIT_EMPTY }	Combine a custom field name with omit-when-empty.

Note

The JSON pragma is only valid on struct elements (see derived types → structures). IGNORE cannot be combined with a name or OMIT_EMPTY — it removes the element from the JSON representation entirely.