E073 - Missing operator function

Some operators are carried out by a function. A comparison of two values of a user-defined type calls <TYPE>_EQUAL, <TYPE>_LESS, or <TYPE>_GREATER, and arithmetic on date and time types calls the standard library, for example ADD_DT_TIME for DATE_AND_TIME + TIME. This error reports an operator whose function is not declared.

Erroneous code example:

TYPE Point : STRUCT
    x, y : DINT;
END_STRUCT
END_TYPE

PROGRAM mainProg
VAR
    a, b : Point;
END_VAR
    IF a = b THEN
    END_IF
END_PROGRAM

To fix this, declare the function the operator needs:

FUNCTION Point_EQUAL : BOOL
VAR_INPUT
    a, b : Point;
END_VAR
    Point_EQUAL := a.x = b.x AND a.y = b.y;
END_FUNCTION

For date and time arithmetic, include the standard library in the build.