Custom string functions

This test case it part of the test suite proposed for new devices.

Test case ID: R0163
Language: ST

Code:

tests2/t0163.st

PROGRAM R0163  
    VAR
        s1,s2,s3,s4: STRING;
        ba,b1,b2 : BYTE;
    END_VAR
    
    ba := 97; // lower case a
    s1 := 'HELO';
    
    b1 := GET_CHAR_AT(s1, 1);
    // _GEB_MSG_(BYTE_TO_STRING(b1));
    _GEB_ASSERT_(b1 = 72); // 'H'
    b1 := GET_CHAR_AT(s1, 4);
    _GEB_ASSERT_(b1 = 79); // 'O'
    b1 := GET_CHAR_AT(s1, 5); // illegal
    _GEB_ASSERT_(b1 = 0); // illegal
    s2 := SET_CHAR_AT(s1, 2, ba); 
    _GEB_ASSERT_(s2 = 'HaLO');
    s2 := SET_CHAR_AT(s2, 1, ba); 
    _GEB_ASSERT_(s2 = 'aaLO');
    s1 := SET_CHAR_AT(s1, 4, ba);
    _GEB_ASSERT_(s1 = 'HELa');
    
END_PROGRAM