Provided by standard library.
Returns the length of a string. Input STR is of type STRING, the return value of the function is type INT.
Example in Function Block Diagram
Example in Structured Text
VarSTRING1 := LEN ('SUSI');
String functions are not "thread safe": When using tasks, string functions may only be used in a single task. If the same function is used in different tasks, there is a danger of overwriting.