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Convert from string containing HEX values to the corresponding chars (E.G. '414141' to 'AAA')

Engineering 🇬🇧
Iaxexo
2021-12-23
2023-07-19

  • Iaxexo - 2021-12-23

    Hy everybody, first post here so please have mercy 😊.

    I'll go straight to the question:
    I read from a file a string that represents with hex values a series of chars in a string
    examples: '41' => 'A'; '535458' => 'STX'.

    I have found the ugliest possible working code:

    PROGRAM PLC_PRG
VAR
    sReadLine, sReverseString: STRING;
    udDBG: UDINT;
    pDBG: POINTER TO STRING;
    i: INT;
END_VAR

sReadline := '535458'; //corresponding string 16#535458 => 10#5461080 => stx
sReadLine := concat('16#',sReadLine); //=>'16#535458'
udDBG := STRING_TO_UDINT(sReadLine); //=>5461080
pDBG := ADR(udDBG);
sReadline := pDBG^;//=>xts
sReverseString:='';

FOR i := 0 TO len(sReadline) DO
    sReverseString := CONCAT(STR1 := sReverseString, STR2 := MID(sReadLine, 1, len(sReadline) - i));//=>stx
END_FOR

    My concern is about robustness and code readability, i do not need great efficiency since the script will run only once during the initialization phase of the system and so does not need to be fast.

    I have the feeling that I am missing something very obvious.
    Can you please point me thowards the right direction? I looked inside the OSCAT library but could not find something satisfying.

    Thank you for your attention and happy holidays.

     

    Last edit: Iaxexo 2021-12-23

  • hermsen

    hermsen - 2021-12-23

    what exactly is your question?

     

    • Iaxexo - 2021-12-24

      Sorry: Is there a better way to do such conversion?
      Are there any functions or librarys that could shorten the code?

       

  • nothinrandom - 2022-01-02

    @laxexo,

    I do not believe there is an available function that handles this conversion for you, so try this out. This handles partial hex (e.g. 20F) and also padded (020F).

    Notes:
    1. Make sure to fill out the _asChar array with all of the chars from the ascii table (e.g. https://www.asciitable.com/). I just tested the first few chars, but the ones of interest should start at 48 (0) and ends at 122 (z), but feel free to adjust further (e.g. from 32 (space) to 126 (~)). If you have other methods that could also use the _asChar, then probably should move it to a global variable to be reused.
    2. Install the Utils library, which has the HEXinASCII_TO_BYTE method.

    FUNCTION sHexToAscii : STRING;
VAR_INPUT
    sInput      : STRING;
END_VAR
VAR
    _bTemp      : BYTE; // get value
    _uiIndex    : UINT; // loop index
    _asChar     : ARRAY[48..122] OF STRING(1) := ['0','1','2','3','4','5','6','7','8','9','0']; // fill
    _uiStrLen   : UINT; // input string length
    _uiStart    : UINT := 0; // loop start index
END_VAR

    // get string length for potential padding
_uiStrLen := len(sInput);
// exit on empty string
IF (_uiStrLen < 1) THEN
    RETURN;
END_IF
// padding for odd (e.g. 20F instead of 020F)
IF (_uiStrLen MOD 2 = 1) THEN
    _bTemp := HEXinASCII_TO_BYTE(sInput[0]); // get low nibble
    IF (_bTemp > 47 AND _bTemp < 123) THEN
        sHexToAscii := CONCAT(sHexToAscii, _aChar[_bTemp]);
    END_IF
    // increment counter
    _uiStart := _uiStart + 1;
END_IF

FOR _uiIndex := _uiStart TO (_uiStrLen - 1) DO
    // get high nibble and low nibble
    _bTemp := SHL(HEXinASCII_TO_BYTE(sInput[_uiIndex]), 4) + HEXinASCII_TO_BYTE(sInput[_uiIndex + 1]);
    // get ascii chars
    IF (_bTemp > 47 AND _bTemp < 123) THEN
        sHexToAscii := CONCAT(sHexToAscii, _asChar[_bTemp]);
    END_IF
    // account for lower nibble
    _uiIndex := _uiIndex + 1;
END_FOR
     

  • Iaxexo - 2022-01-11

    Nice solution, thank you! I hoped for something "easier" but I am beginning to understand that this is not a happy place for string manipulations :)

     

  • Iaxexo - 2022-01-11
     

    Last edit: Iaxexo 2022-01-11

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