Identifier¶

Rules for identifier designation¶

Namenskonvention

Rules for identifiers of variables

• An identifier must not contain spaces or special characters.
• This means that CODESYS ignores uppercase/lowercase. VAR1 and var1 indicate the same variable.
• CODESYS recognizes underscores. For example, A_BCD and AB_CD are treated as two different identifiers. Multiple consecutive underscores are not permitted.
• The length of an identifier is unlimited.

Rules for multiple use of identifiers (namespaces)

• You are permitted to use an identifier locally only one time.

• An identifier is not permitted to be identical to a keyword (for example, variable type).

• You are permitted to use an identifier globally several times. If a local variable has the same name as a global variable, then the local variable has priority within the POU.

• A variable that is defined in a global variable list can have the same name as a variable defined in another GVL. CODESYS provides features that extend the standard for the namespace and scope of variables:

  • Global namespace operator: An instance path that begins with a dot always opens a global namespace. If there is a local variable (for example, ivar) that has the same name as a global variable, then you refer to the global variable as .ivar.

  • The name of a global variable list can define the namespace uniquely for the include variables. Therefore, you can declare variables with the same name in different global variables list and still uniquely reference by prepending the list name.

    For example, globlist1.ivar := globlist2.ivar; (* ivar from GVL globlist2 is copied to ivar in GVL globlist1 *).

  • Variables that are defined in the global variable list of a library included in the project can be referenced uniquely with the following syntax: <namespace library>.<GVL name>.<variable name>.

    For example, globlist1.ivar := lib1.globlist1.ivar (* ivar from GVL globlist1 in library lib1 is copied to ivar in GVL globlist1 *).

• When inserting a library, you also use the library manager to define a namespace. In this way, you can make unique references to library blocks and library via <namespace library>.<block name\|variable name>. Please note that when libraries are nested, you must reference the namespaces of all libraries are in succession

  Example: If Lib1 is referenced by Lib0, then the block func in Lib1 is addressed via Lib0.Lib1.fun: ivar := Lib0.Lib1.fun(4, 5); (* return value from func is copied to variable ivar in the project *)

See also

• Data Types
• Variable Types and Special Variables

Recommendations¶

We recommend that you apply the following rules in addition to the items that you have to consider specifically for variables declaration. By doing this, you will achieve the best possible harmonization when assigning names.

Recommendations for variable names¶

In all applications and libraries, you should name variables with Hungarian notation, when possible:

For each variable, find a short, meaningful, English description for the base name. The first letter of words in the base name is uppercase and all other letters are lowercase (for example, FileSize).

Append lowercase prefixes to the base name depending on the data type of the variables:

*: x is used intentionally as a prefix for Boolean variables to differentiate from BYTE and to accommodate IEC programmers.

bySubIndix: BYTE;

xFlag: BOOL;

udiCounter: UDINT;

Recommendations for variable names CODESYS V3.x libraries¶

Recommendations for identifiers for user-defined data types (DUT)¶

Recommendations for identifiers for user-defined data types (DUT) in CODESYS V3 libraries¶

Recommendations for identifiers for POUs, functions, function blocks, programs¶

Recommendations for identifiers for POUs in CODESYS V3 libraries¶

Recommendations for identifiers for visualizations¶

See also

• Declaring Variables