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Variable: RETAIN

Retain variables are declared by the keyword RETAIN is added in programming objects in the scope VAR, VAR_INPUT, VAR_OUTPUT, VAR_IN_OUT, VAR_STAT, or VAR_GLOBAL.

Syntax for the declaration

<scope> RETAIN
    <identifier>: <data type> ( := <initialization> )? // ( ... )? : Optional
END_VAR
<scope> : VAR | VAR_INPUT | VAR_OUTPUT | VAR_IN_OUT | VAR_STAT | VAR_GLOBAL

An assignment of inputs, outputs, or memory addresses with the AT keyword is not permitted.

Example 98. Example

In a POU

VAR RETAIN
        iVarRetain: INT;
END_VAR

In a GVL

VAR_GLOBAL RETAIN
        g_iVarRetain: INT;
END_VAR


Possible declaration locations

Locally in a program

Only the variable is located in the retain memory area.

Note

When using redundancy, the entire program with all of its data is located in the retain memory area.

Globally in a global variable list

Only the variable is located in the retain memory area.

Note

When using redundancy, the entire global variable list with all of its data is located in the retain memory area.

Locally in a function block

The entire instance of the function block with all of its data is located in the retain memory area. Only the declared retain variable is protected.

Locally in a function

The variable is not located in the retain memory area. This declaration does not have any effect.

Locally and persistently in a function

The variable is not located in the retain memory area. This declaration does not have any effect.

Tip

Whenever possible, avoid using RETAIN to mark the variables of a function block.

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