Converting an integer into three hexadecimal variables

Question

I have a problem when trying to convert a 6 digits number into three hexa decimal numbers I'm using an Arduino Nano I already did the following

• Converting to string Hexa
• Cutting string with substring into three other strings But my CAN library want to receive char variables So i did convert the strings to char but it lack the "0x00" and use instead just "00" And my can library (mcp_can) doesn't want that

Thanks you for reading this

• Tried sending the strings without the "0x" suffix : didn't work
• Tried to add the "0x" suffix to the char : didn't work
• Tried to send decimal : didn't work
• If I send manually something in hexa with the "0x" suffix it work

Edit : The code, i think it's horrible

    void splitAndConvert(int bignumber)
    { 
      int ID6;
      int ID7;
      int ID8; 
      String FirstPart; 
      String SecondPart;
      String ThirdPart;

      String BigNumberHexa = String(bignumber, HEX);
      
      if (BigNumberHexa.length() <= 2) {
        FirstPart = "0"; 
        SecondPart = "0";    
        ThirdPart = BigNumberHexa;
      }
      else if (BigNumberHexa.length() < 4) {
        FirstPart = "0";
        SecondPart = BigNumberHexa.substring(0,BigNumberHexa.length() - 2);
        ThirdPart = BigNumberHexa.substring(BigNumberHexa.length() - 2,BigNumberHexa.length());
      }
      else if (BigNumberHexa.length() < 6) {
        FirstPart = BigNumberHexa.substring(0,BigNumberHexa.length()-4);
        SecondPart = BigNumberHexa.substring(BigNumberHexa.length() - 4,BigNumberHexa.length() - 2);
        ThirdPart = BigNumberHexa.substring(BigNumberHexa.length() - 2,BigNumberHexa.length());
      }
      else {

      }
      ID6 = ThirdPart.toInt();
      ID7 = SecondPart.toInt();
      ID8 = ThirdPart.toInt();
            
      unsigned char DataToSend[8] = {0x00, 0x00, 0x00, 0x00, 0x00, ID6, ID7, ID8};
      can.sendMsgBuf(0x001, 0, 8, DataToSend);
}

Answer 1

If I understand what you are trying to archieve, your code should be:

void splitAndConvert(int bignumber)
{ 
  byte ID6 = 0x00;                    // int has only two bytes on AVR architecture
  byte ID7 = (bignumber >> 8) & 0xFF; // shift right by 8 bits and mask (mask is unnecessary if you are assigning it into byte)
  byte ID8 = bignumber & 0xFF;        // again bitmask is unnecessary, it'll be cut off to fit into the byte anyway
        
  unsigned char DataToSend[8] = {0x00, 0x00, 0x00, 0x00, 0x00, ID6, ID7, ID8};
  can.sendMsgBuf(0x001, 0, 8, DataToSend);
}

And if you really want to have bigger numbers:

void splitAndConvert(int32_t bignumber)
{ 
  byte ID6 = bignumber >> 16; // shift right by 16b, ommited unnecessary mask
  byte ID7 = bignumber >> 8;  // shift right by 8b 
  byte ID8 = bignumber;       // LSB will be assigned (but with ints you'll have to use bitmasking)
        
  unsigned char DataToSend[8] = {0x00, 0x00, 0x00, 0x00, 0x00, ID6, ID7, ID8};
  can.sendMsgBuf(0x001, 0, 8, DataToSend);
}