Unresolved constant

A CONSTANT declaration could not be resolved to a compile-time value.

This error is reported when the compiler cannot determine a valid constant initializer, for example when:

• the initializer references non-constant values,
• the initializer contains non-constant operations/calls,
• a referenced constant is itself unresolved,
• a CONSTANT has no explicit initializer and no usable default can be derived from its type.

Example

TYPE MyInt : INT; END_TYPE

VAR_GLOBAL CONSTANT
    // No explicit initializer, and no type default available
    a : MyInt;

    // Not a constant expression
    b : INT := someVar + 1;
END_VAR

Possible fixes

• Provide an explicit compile-time initializer, e.g. a : MyInt := 0;.
• Ensure all referenced symbols in the initializer are themselves constants.
• Replace non-constant calls/operations with compile-time expressions.
• If relying on implicit defaults, define a default on the declared type.