Recommendations on the Naming of Identifiers

Overview

Identifiers are defined:

oat the declaration of variables (variable name)

oat the declaration of user-defined data types

oat the creation of POUs (functions, function blocks, programs)

In addition to the general items to be considered when defining an identifier (refer to chapter General Information on variables declaration), consider the following recommendations in order to make the naming as unique as possible:

oVariable names 

oVariable names in Libraries 

oUser-defined data types (DUTs) in Libraries

oFunctions, Function blocks, Programs (POU), Actions

oPOUs in Libraries

Variable Names

For naming variables in applications and libraries, follow the Hungarian notation as far as possible.

Find for each variable a meaningful, short description. This is used as the base name. Use a capital letter for each word of the base name. Use small letters for the rest (example: FileSize).

Simple declaration

Examples for simple declarations:

bySubIndex: BYTE;

sFileName: STRING;

udiCounter: UDINT;

Nested declaration

Example for a nested declaration where the prefixes are attached to each other in the order of the declarations:

pabyTelegramData: POINTER TO ARRAY [0..7] OF BYTE;

Function block instances and variables of user-defined data types

Function block instances and variables of user-defined data types get a shortcut for the function block or the data type name as a prefix (for example: sdo).

Example

cansdoReceivedTelegram: CAN_SDOTelegram;

TYPE CAN_SDOTelegram :     (* prefix: sdo *)
STRUCT
  wIndex:WORD;
  bySubIndex:BYTE;
  byLen:BYTE;
  aby: ARRAY [0..3] OF BYTE;
END_STRUCT
END_TYPE

Local constants

Local constants (c) start with prefix c and an attached underscore, followed by the type prefix and the variable name.

Example

VAR CONSTANT
  c_uiSyncID: UINT := 16#80;
END_VAR

Global variables and global constants

Global variables are prefixed by g_ and global constants are prefixed by gc_.

Example

VAR_GLOBAL
  g_iTest: INT;
END_VAR
VAR_GLOBAL CONSTANT
  gc_dwExample: DWORD;
END_VAR

Variable Names in Libraries

Structure

Basically, refer to the above description for variable names. Use the library namespace as prefix, when accessing a variable in your application code.

Example

g_iTest: INT; (declaration)
CAN.g_iTest (implementation, call in an application program

User-Defined Data Types (DUT) in Libraries

Structure

The name of each structure data type consists of a short expressive description (for example, SDOTelegram) of the structure.

Example (in library with namespace CAL):

TYPE Day :(
MONDAY,
TUESDAY,
WEDNESDAY,
THURSDAY,
FRIDAY,
SATURDAY,
SUNDAY);

Declaration:

eToday: CAL.Day;

Use in application:

IF eToday = CAL.Day.MONDAY THEN

NOTE: Consider the usage of the namespace when using DUTs or enumerations declared in libraries.

Functions, Function Blocks, Programs (POU), Actions

The names of functions, function blocks, and programs are prefixed by an expressive short name of the POU (for example, SendTelegram). As with variables, the first letter of a word of the POU name should always be a capital letter whereas the others should be small letters. It is recommended to compose the name of the POU of a verb and a substantive.

Example

FUNCTION_BLOCK SendTelegram (* prefix: canst *)

In the declaration part, provide a short description of the POU as a comment. Further on, the inputs and outputs should be provided with comments. In case of function blocks, insert the associated prefix for set-up instances directly after the name.

Actions

Actions do not get a prefix. Only those actions that are to be called only internally that is by the POU itself, start with prv_.

POUs in Libraries

Structure

For creating method names, the same rules apply as for actions. Enter English comments for possible inputs of a method. Add a short description of a method to its declaration. Start interface names with letter I; for example, ICANDevice.

NOTE: Consider the usage of the namespace when using POUs declared in libraries.