String with comma-separated values and newlines: split values and create arrays for each newline

<xsl:stylesheet
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:mf="http://example.com/mf"
  exclude-result-prefixes="xs mf"
  version="2.0">

  <xsl:function name="mf:sub-sequences" as="xs:string*">
    <xsl:param name="input" as="xs:string"/>
    <xsl:param name="min-length" as="xs:integer"/>
    <xsl:sequence select="reverse(
                            for $length in $min-length to string-length($input)
                            return substring($input, 1, $length)
                          )"/>
  </xsl:function>

  <xsl:template name="main">
    <xsl:variable name="s" select="'12345'"/>
    <xsl:value-of select="mf:sub-sequences($s, 2)" separator=","/>
  </xsl:template>

</xsl:stylesheet>

'1,2\n3'.split(/[,\n]/)

Declare @YourTable table (ID int,Data varchar(max))
Insert Into @YourTable values
(1,'abc,def'),
(2,'def,abc'),
(3,'def,ghi')

Select A.ID
      ,B.*
      ,ColName = 'Data'+cast(DENSE_RANK() over (Order By RetVal) as varchar(25))
Into #Temp
From @YourTable A
Cross Apply (
              Select RetSeq = Row_Number() over (Order By (Select null))
                    ,RetVal = LTrim(RTrim(B.i.value('(./text())[1]', 'varchar(max)')))
              From (Select x = Cast('<x>'+ Replace(A.Data,',','</x><x>')+'</x>' as xml).query('.')) as A 
              Cross Apply x.nodes('x') AS B(i)
             ) B


Declare @SQL varchar(max)
Select  @SQL = Stuff((Select Distinct ',' + QuoteName(ColName) From #Temp For XML Path('')),1,1,'')   
Select  @SQL = 'Select ID,' + @SQL + ' 
                From (Select ID,ColName,RetVal From #Temp) A
                Pivot (max(RetVal) For ColName in (' + @SQL + ') ) p'

Exec(@SQL);

ID  Data1   Data2   Data3
1   abc     def     NULL
2   abc     def     NULL
3   NULL    def     ghi

typedef struct {
    int A = 0;
    int B = 0;
    int C = 0;
    int D = 0;
    int E = 0;
    int F = 0;
    char G = 0;
    int H = 0;
} Line;

typedef void (*LineHandler)(Line data);

bool line_parser(char c, LineHandler line_handler) {
    static Line data;
    static int value = 0;
    static byte state = 0;
    bool complete = false;

    // ignore the carriage return character
    if (c == '\r') return complete;

    if (state < 8) {
        if (isdigit(c)) {
            value = value*10 + c-'0';  // add the digit
        }
        else if (c == ',' || c == '\n') {
            // if a comma or end of line is found, save the value
            switch (state) {
                case 0: data.A = value; break;
                case 1: data.B = value; break;
                case 2: data.C = value; break;
                case 3: data.D = value; break;
                case 4: data.E = value; break;
                // the F and G are set when the letter is found
                case 7: data.H = value; break;
            }
            // advance the parsing state and reset the value
            state++;
            value = 0;
        }
        else if (state == 5 && isalpha(c)) { // if parsing the 6th number and a letter is found
            data.F = value; // save the 6th number
            data.G = c; // save the letter
            state += 2; // advance to parsing the 8th value
            value = 0; // reset the value
        }
        else
            state = 10; // unexpected character; stop the parser
    }
    if (c == '\n') {
        if (state == 8) {
            //got complete line
            line_handler(data);
            complete = true;
        }
        else {
            // parsing failed
        }
        // reset the parser
        value = 0;
        state = 0;
    }
    return complete;
}

void handle_line(Line data) {
    // just print out the data
    Serial.println("Line:");
    Serial.print("A = ");
    Serial.println(data.A);
    Serial.print("B = ");
    Serial.println(data.B);
    Serial.print("C = ");
    Serial.println(data.C);
    Serial.print("D = ");
    Serial.println(data.D);
    Serial.print("E = ");
    Serial.println(data.E);
    Serial.print("F = ");
    Serial.println(data.F);
    Serial.print("G = ");
    Serial.println(data.G);
    Serial.print("H = ");
    Serial.println(data.H);
    Serial.println();
}

void setup() {
    Serial.begin(115200);
}

void loop() {
    if (Serial.available()) {
        line_parser(Serial.read(), handle_line);
    }
}

54,125,11045,11,78,4H45
invalid line
11,22,33,44,55,66K88
30,30,20,10,50,50M20

Line:
A = 54
B = 125
C = 11045
D = 11
E = 78
F = 4
G = H
H = 45

Line:
A = 11
B = 22
C = 33
D = 44
E = 55
F = 66
G = K
H = 88

Line:
A = 30
B = 30
C = 20
D = 10
E = 50
F = 50
G = M
H = 20