IEC_COMPLIANCE.md

IEC 61131-3 Compliance

STruC++ implements the Structured Text (ST) language from IEC 61131-3. This document lists supported features and known gaps. The compiler also supports common CODESYS extensions where noted.

Data Types

Type	Status	Notes
BOOL	Supported
BYTE, WORD, DWORD, LWORD	Supported
SINT, INT, DINT, LINT	Supported
USINT, UINT, UDINT, ULINT	Supported
REAL, LREAL	Supported
TIME	Supported	Nanosecond precision, int64_t storage
DATE	Supported
TIME_OF_DAY	Supported
DATE_AND_TIME	Supported
LTIME, LDATE, LTOD, LDT	Supported	64-bit time types with nanosecond precision
STRING	Supported	Parameterized length: STRING(N), default 254
WSTRING	Supported	Parameterized length: WSTRING(N)
CHAR, WCHAR	Supported

Derived Types

Type	Status	Notes
TYPE ... END_TYPE	Supported	Type aliases
STRUCT ... END_STRUCT	Supported	With nested structs
Enumerations	Supported	With optional base type
ARRAY (1D)	Supported	Arbitrary bounds: ARRAY[1..10] OF INT
ARRAY (2D)	Supported	ARRAY[1..3, 1..4] OF REAL
ARRAY (3D)	Supported	ARRAY[1..3, 1..4, 1..5] OF INT
ARRAY[*] (VLA)	Supported	Variable-length array parameters
Subranges	Supported	Runtime validation
REF_TO	Supported	IEC reference type (explicit dereference)
REFERENCE_TO	Supported	CODESYS reference type (implicit dereference)
POINTER TO	Supported	CODESYS pointer type with dereference via ^

Not Implemented

Type	Notes
UNION	CODESYS extension

Program Organization Units

POU	Status	Notes
PROGRAM	Supported	With CONFIGURATION/RESOURCE/TASK structure
FUNCTION	Supported	With return type, all parameter modes
FUNCTION_BLOCK	Supported	Instantiation, invocation, member access
INTERFACE	Supported	Method and property signatures

Variable Declarations

Feature	Status	Notes
VAR	Supported	Local variables
VAR_INPUT	Supported	Input parameters
VAR_OUTPUT	Supported	Output parameters
VAR_IN_OUT	Supported	Pass-by-reference parameters
VAR_EXTERNAL	Supported	External references to VAR_GLOBAL
VAR_GLOBAL	Supported	Global variables
CONSTANT	Supported	Compile-time constants
RETAIN	Supported	Tracked in retain variable table
NON_RETAIN	Supported
AT %IX0.0	Supported	Located variables (I/Q/M areas, X/B/W/D/L sizes)
Multiple names	Supported	a, b, c : INT := 0;
Initialization	Supported	:= expression

Operators and Expressions

Category	Operators	Status
Arithmetic	+, -, *, /, MOD, **	Supported
Comparison	=, <>, <, >, <=, >=	Supported
Logical	AND, OR, XOR, NOT	Supported
Bitwise	AND, OR, XOR, NOT (on bit types)	Supported
Bit shift	SHL, SHR, ROL, ROR	Supported
Assignment	:=	Supported
Reference assign	REF=	Supported
Dereference	^, DREF()	Supported
Reference	REF()	Supported
Parentheses	( )	Supported
Function call	name(args)	Supported (positional + named)
Method call	obj.method(args)	Supported
Array access	arr[i], arr[i, j]	Supported
Field access	struct.field	Supported
Typed literals	INT#5, DINT#42, REAL#3.14	Supported
NEW	__NEW(type), __NEW(type, size)	Supported
DELETE	__DELETE(ptr)	Supported

Control Structures

Structure	Status	Notes
IF / ELSIF / ELSE / END_IF	Supported
FOR / TO / BY / DO / END_FOR	Supported	With optional BY (step)
WHILE / DO / END_WHILE	Supported
REPEAT / UNTIL / END_REPEAT	Supported
CASE / OF / END_CASE	Supported	Integer, bit, and enum selectors
EXIT	Supported	Break from loop
RETURN	Supported	Early return from POU

OOP Extensions

Feature	Status	Notes
Methods	Supported	On FUNCTION_BLOCK, with return types
Properties (GET/SET)	Supported	Virtual getter/setter methods in C++
Inheritance (EXTENDS)	Supported	Single inheritance
Interfaces (IMPLEMENTS)	Supported	Multiple interfaces, generates C++ abstract classes
ABSTRACT	Supported	Abstract FB (no instantiation) and abstract methods (pure virtual)
FINAL	Supported	Sealed FB and methods
OVERRIDE	Supported	Method override with C++ override specifier
PUBLIC/PRIVATE/PROTECTED	Supported	Access modifiers
THIS	Supported	Self-reference in methods

Standard Functions

All IEC 61131-3 standard functions are implemented in the C++ runtime:

Category	Functions
Numeric	ABS, SQRT, LN, LOG, EXP, EXPT
Trigonometric	SIN, COS, TAN, ASIN, ACOS, ATAN, ATAN2
Selection	SEL, MIN, MAX, LIMIT, MUX
Comparison	GT, GE, EQ, LE, LT, NE
Bitwise	AND, OR, XOR, NOT, MOVE
Bit Shift	SHL, SHR, ROL, ROR
Type Conversion	TO (INT_TO_REAL, DINT_TO_STRING, etc.)
String	LEN, LEFT, RIGHT, MID, CONCAT, FIND, REPLACE, INSERT, DELETE, UPPER, LOWER, TRIM
System	ADR, SIZEOF

Standard Function Blocks

Bundled as a compiled .stlib library (libs/iec-standard-fb.stlib):

FB	Description
TON	On-delay timer
TOF	Off-delay timer
TP	Pulse timer
CTU	Count-up counter
CTD	Count-down counter
CTUD	Up/down counter
R_TRIG	Rising edge detector
F_TRIG	Falling edge detector
SR	Set-dominant bistable
RS	Reset-dominant bistable

Project Structure

Feature	Status	Notes
CONFIGURATION	Supported
RESOURCE ... ON	Supported
TASK ... WITH INTERVAL	Supported
Program instances	Supported	name : programType with task assignment
VAR_GLOBAL in configuration	Supported
Namespace configuration	Supported	Via pragmas

Language Extensions

Feature	Status	Notes
Nested comments (* (* *) *)	Supported	Arbitrary nesting depth
Pragmas {...}	Supported	Including {external} for inline C++
Inline C++	Supported	Via {external ...} pragma blocks
Inline function calls	Supported	Via {call ...} pragma
Global constants (-D)	Supported	CLI -D NAME=VALUE, emits constexpr
Dynamic memory	Supported	__NEW(type), __DELETE(ptr)
POINTER TO	Supported	Full pointer type with dereference
Typed literals	Supported	INT#5, DINT#42, REAL#3.14

Not Yet Implemented

Feature	Notes
UNION	CODESYS union type
FB_Init / FB_Exit	Constructor/destructor lifecycle methods
__QUERYINTERFACE	Runtime interface query
Bit access (var.%X0)	Individual bit addressing
ACTION blocks	Named action blocks
TRY/CATCH/FINALLY	Exception handling
Generics	Parameterized types
Conditional compilation	Preprocessor-style conditionals