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Variable: CONSTANT

Constant variables are declared in global variable lists or in the declaration part of programming objects. In implementations, constant variables can be accessed as read-only via the instance path.

Syntax 

<scope> CONSTANT
    <identifier> : <data type> := <initial value> ;
END_VAR

<scope> : VAR | VAR_INPUT | VAR_STAT | VAR_GLOBAL
<data type>: <elementary data type> | <user defined data type> | <function block>
<initial value> : <literal value> | <identifier> | <expression>

Always assign an initialization value when declaring a constant variable. Then the constant cannot be written any more.

Example

Declaration 

VAR CONSTANT
        c_rTAXFACTOR : REAL := 1.19;
END_VAR

Call 

rPrice := rValue * c_rTAXFACTOR;

You have read-only access to constant variables in an implementation. Constant variables are located to the right of the assignment operator.

For more information, see: ⮫ “Operands ”, ⮫ “Constants and literals ”, ⮫ “Variables ”, ⮫ “Other ”