IEC WStrings always contain the number of characters in double bytes. Preceding is a 4 byte header. The character string must be terminated with two bytes containing a zero character. All IEC WStrings use internally a structure IecWString. Though the string is defined as using double characters, also 4 byte UTF-16 characters can be used. The length of the string is shortened.
The default string IECWString80's maximum size is 160 bytes, which is set implicitly. The memory representation is 80 characters (double byte) of string content + 4 byte header + 2 byte terminating zeroes.
The IEC user string type can be defined to the users needs. The memory representation is the amount of characters in the string (double byte) + 4 byte header + 2 byte terminating zeroes. For user defined strings, a structure of type IecWString is necessary. The Init() method of this string must set its maximum character size.
The IecWString structure contains the member m_cap The member m_cap must be initialized to the required character size before use. A field of the type IecWString must have the [FieldOffset(0)] attribute, to define the beginning of the IEC strings physical representation.
The sample function block adds to an input string another string. One character is a special 4 byte UTF-16 character.