Definitions

The compiler supports the definition of aliases. An alias is a unique identifier that can be used in programs to replace another text. Definitions are typically used for replacing a constant expression and ease the maintenance of programs.

There are two levels of definitions:

Global to all programs of a project.
Local to one program.

Local definitions are edited together with the corresponding program. Use the View / Local Defines menu command when editing a program to open its local definitions.

Hint: Alias declared as global define can be used as variable name in a fieldbus configuration. An alias can replace a full variable name or an index in case of an array element.

Definitions are entered in a text editor. Each definition must be entered on one line of text according to the following syntax:

#define Identifier Equivalence (* comments *)

Example

#define OFF FALSE (* redefinition of FALSE constant *)
#define PI 3.14 (* numerical constant *)
#define ALARM (bLevel > 100) (* complex expression *)

Please note: There is no semicolon (;) at the end of the expression.

You can use a definition within the contents of another definition. The definition used in the other one must be declared first.

Example

#define PI 3.14
#define TWOPI (PI * 2.0)

Information

A definition may be empty, for example:

#define CONDITION

Defined word can be used for directing the conditional compiling directives.

You can enter #define lines directly in the source code of programs in IL or ST languages.

The use of definitions may disturb the program monitoring and make error reports more complex. It is recommended to restrict the use of definitions to simple expressions that have no risk to lead to a misunderstanding when reading or debugging a program.

System definitions

The following words are predefined by the compiler and can be used in the programs:

Word	Description
__DATE__	Date stamp of compiling expressed as a string constant expression Format is: Year/Month/Day-Hours-Minutes.
__MACHINE__	Name of the machine where compiling is run, expressed as a string constant expression.
__USER__	Name of the user where compiling is run, expressed as a string constant expression.
__APPNAME__	Name of the project, expressed as a string constant expression.

Example

The following ST program sets variables declared as STRING(255):

   strDate := __DATE__;
   strMachine := __MACHINE__;
   strUser := __USER__;
strProject := __APPNAME__;

Result:

strDate is '2007/11/25-10:45'
strMachine is 'LaptopJX'
strUser is 'John'
strProject is 'Project1'

Definitions

IEC 61131-3 Automation platform > IEC 61131-3 Programming Environment > Definitions

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