Strings

According to the PLCopen mapping, the PLC data types STRING and WSTRING are both mapped to the OPC UA data types String. The difference lies in the internal storage:

• STRING: Characters are 1 byte long.
• WSTRING: Characters are 2 bytes long.

Both data types are explained below. For more details, please refer to the TwinCAT 3 PLC documentation.

STRING

The STRING data type can be interpreted in TwinCAT as either Latin-1 or UTF-8.
The interpretation is controlled via the {attribute 'TcEncoding'} attribute:

• Latin-1 is used without an attribute.
• UTF-8 is used with attribute.

Samples:

// Standard: Latin-1
sMyStringText   : STRING := 'This is a STRING';

// UTF-8 from STRING
{attribute 'TcEncoding' := 'UTF-8'}
sMyUTF8Text1    : STRING  := sLiteral_TO_UTF8('The dinner costs 30 €.');

// UFT-8 from WSTRING
{attribute 'TcEncoding' := 'UTF-8'}
sMyUTF8Text2    : STRING  := wsLiteral_TO_UTF8("The dinner costs 30 €.");

// UFT-8 simple STRING
{attribute 'TcEncoding' := 'UTF-8'}
sMyUTF8Text3    : STRING  := 'Hello World.';

WSTRING

The WSTRING data type follows the UCS2 coding (2 bytes per character). Initialization always takes place with double quotation marks.

Sample:

wsMyWSTRING : WSTRING := "This is a WSTRING.";