Identifiers for variables and instances

When naming variables and instances, consider the following points:

Prefixes of variable and instance names are written in lower case.
The first character after the prefix is capitalized (enable option First character after prefix should be an upper case letter of naming conventions from Static Analysis, see the following note on Static Analysis).

Static Analysis:

Also note the option to check programming conventions using TE1200 PLC Static Analysis.

Prefixes:

1) Variables of elementary and dynamic data types:

Type	Prefix	Description	Declaration example	Call example	Static Analysis Name Convention ID
SINT, USINT, INT, UINT, DINT, UDINT, LINT, ULINT, BYTE, WORD, DWORD, LWORD, XINT, UXINT, XWORD	n	Integer, bit-based number	nErrorID : UDINT; nSize : UINT; nMask : WORD; nMessages : UINT;	nErrorID := 16#745; nSize := SIZEOF(ST_BufferEntry); nMask := nMask & 16#0FF0; nMessages := 3;	NC0005-NC0016, NC0035, NC0037, NC0038, NC0160
BOOL, BIT	b	boolean (bit)	bConfigured bReset		NC0003, NC0004
REAL, LREAL	f	float	fPosition		NC0017, NC0018
STRING	s	string	sNetID		NC0019
WSTRING	ws	wide string (unicode)	wsRouteName		NC0020
TIME, LTIME	t	time	tDelay		NC0021, NC0022
TIME_OF_DAY	td	time of day	tdClockTime		NC0025
DATE	d	date	dProductionStart		NC0023
DATE_AND_TIME	dt	date and time	dtProductionStart		NC0024
ARRAY[...] OF ...	a	array	aMessages		NC0030
POINTER TO ...	p	pointer	pData pNextProduct	pData := ADR(aBuffer);	NC0026
POINTER TO POINTER TO ...	pp	Nested pointer	ppData
POINTER TO INTERFACE	pip	Pointer to an interface	pipCylinder
REFERENCE TO ... 1) as method input 2) in other cases	1) according to the basic data type of the reference 2) ref	Reference	1) nData (with REFERENCE TO INT) 2) refSize	1) SampleMethod(nData := <…>) 2) refSize REF= nSize;	NC0027

Pointer:

Typed pointers are preferred over untyped pointers for safety reasons.
Pointers should be declared as POINTER TO <data type>, where <data type> matches the data type of the variable to which the pointer refers.
A pointer pointing to an array should be declared as POINTER TO ARRAY [...] OF <data type>, where <data type> matches the data type of the array to which the pointer refers.
If the data type of the variable to which a pointer points is unknown and therefore cannot be typified, it should be declared as POINTER TO BYTE (or PVOID). The data type DWORD cannot be used as pointer for reasons of 64 bit compatibility.
The content operator '^' is used for dereferencing a pointer.
Particular attention should be paid to the validity of the address to which a pointer points.

Sample 1:

nSample       : INT;
pSampleToInt  : POINTER TO INT;

pSampleToInt  := ADR(nSample)
pSampleToInt^ := 123;              // Result: nSample = 123

Sample 2:

aSample                   : ARRAY[1..3] OF LREAL;
pSampleToArrayOfLreal     : POINTER TO ARRAY[1..3] OF LREAL;

pSampleToArrayOfLreal     := ADR(aSample);
pSampleToArrayOfLreal^[2] := 4.56; // Result: aSample[2] = 4.56

Pointer arithmetic / pointer comparisons:

If possible, pointer arithmetic and the use of comparison operators on pointers should be avoided for safety reasons (e.g. increments such as [pSampleToLreal: = pSampleToLreal + SIZEOF(LREAL)] or pointer comparisons using >, >=, <, <=).
If you cannot do without these operations, use them at most within an array.
It is particularly important to ensure that the pointers point to elements of the same array, and that the address range of the array is complied with.

2) Instances of objects, and user-defined data types:

Instances of function blocks that are defined in the IEC61131 standard and are of fundamental importance (R_TRIG, TON ...) have no other prefix. Example for correct naming:

fbAdsTimer : TON;

Type	Prefix	Description	Declaration example	Call example	Static Analysis Name Convention ID
FUNCTION_BLOCK	fb	Instance of a function block	fbWritePersData : FB_WritePersistentData;	fbWritePersData();	NC0031
STRUCT	st	Instance of a structure	stBufferEntry : ST_BufferEntry;	stBufferEntry.nCounter := 5;	NC0032
ENUM	e	Instance of an enumeration	eMachineState : E_MachineState; eQuality : E_Quality;	eMachineState := E_MachineState.Stop; eQuality := E_Quality.Good;	NC0029
TYPE (Alias)	according to the internal data type	Instance of an alias type	nNibble : T_Nibble; sNetId : T_AmsNetId;	nNibble := 16#1; sNetId := '1.2.3.4.5.6';	NC0033 See also: Placeholder {datatype}
INTERFACE	ip	Instance of an interface	ipCylinder : I_Cylinder;	ipCylinder := fbCylinderBase;	NC0036
UNION	u	Instance of a union	uCtrl : U_Control;	uCtrl.aRegister[1] := 16#02;	NC0034

3) Other:

Type	Prefix	Description	Declaration example	Static Analysis Note
Nested types	Only according to the outer type Exception 1: 'pp' for POINTER TO POINTER TO Exception 2: 'pip' for POINTER TO INTERFACE		pTelegramData : POINTER TO ARRAY[0..7] OF BYTE;	Disable option Recursive prefixes for combinable data types See also: Naming conventions (2)
Local and global constants	c		VAR CONSTANT cSyncID : UINT := 16#80; END_VAR VAR_GLOBAL CONSTANT cLowerThreshold : UDINT := 9; cOptionMove : DWORD := 16#04; END_VAR	NC0062, NC0070
Global variables		The same naming rules apply for global variables. (Do not add a second prefix to the variable names.)	VAR_GLOBAL nProducedUnits : UINT; END_VAR	Disable option Combine scope prefix with data type prefix See also: Naming conventions (2)
HRESULT	hr		hrErrorCode : HRESULT;	NC0160
PVOID	p	pointer	pData : PVOID;	NC0160
GUID		No prefix is assigned for GUID.
AT%I*	optional before the data type prefix: I	allocated input	fActPos AT%I: LREAL; oder: IfActPos AT%I: LREAL;
AT%Q*	optional before the data type prefix: O	allocated output	fSetPos AT%Q: LREAL; oder: OfSetPos AT%Q: LREAL;

Allocated inputs or outputs can have an optional additional prefix 'I' or 'O' before the data type prefix. For instances, it represents the only prefix that is capitalized. The decision for or against the use of this optional prefix should be consistent, so that the name of allocated variables is uniform across the project.