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R008_LimitStringLength.md

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R008_LimitStringLength.md

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Recommendation R008: Specify string lengths

String data types (STRING and WSTRING) can be declared with an optional maximum capacity. The limit is 254 for STRING and 16328 for WSTRING.

If strings are passed as formal parameters via the VAR_INPUT and VAR_OUTPUT sections of a FUNCTION_BLOCK they are passed by value. In this case it is recommended to specify the required string length via a symbolic constant.

Example

VAR CONSTANT
    MSG_LENGTH : DINT := DINT#300;
END_VAR
    
VAR_INPUT
    statusMessage : WSTRING[MSG_LENGTH];
END_VAR

Note

The usage of string variables with appropriate size limitation also reduces the memory allocated by the system.

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