Char to Hex Add 00

Projects Programming
1

Hello ,

I need to add 00 to each character in a message and then write them as a byte in HEX:

68 07 01 01 00 00 00 0A 09 00 00 65 31 00 32 00 33 00 10

31 00 32 00 33 00 = Text "123"

00 0A = The length of the total payload "09 00 00 65 31 00 32 00 33 00"

I am not familiar with C, how can i char msgArray[] = "123"; add the 00 after each char and calculate the length of the payload?

I have tried the serial.write and this works when sending each byte separately but i want a function to enter the the text msgArray .

Any help is appreciated.

2

You could use a simple for loop and "strlen(msgArray)"

3

You could start with this:

char msgArray[30];
byte value = 123;
sprintf(msgArray,"%02x",value);  //format in ASCII hex

31 00 32 00 33 00 = Text "123"

Not clear what you mean by the above. Those two representations are not the same.

char msgArray[] = "123" is the same as
char msgArray[] = {0x31,0x32,0x33,0x00}

4

Please give a better example of what you want to do. The original post is contradictory and confusing.

how can i char msgArray[] = "123"; add the 00 after each char

Maybe this will help

const char msgArray[] = "123";
char output[30]={0};
byte j=0;  //output index

for (byte i=0; i<strlen(msgArray); i++) {
output[j++]=msgArray[i];
output[j++]=0;
}
byte output_len=j--; //length of output array
5

arrayTrans

The above requirements can be made by the following codes:

char srcA[] = {'1', '2', '3'};
char desA[6];

void setup() 
{
  Serial.begin(9600);
  for(int i = 0, j = 0; i<3; i++, j++)  //building new array
  {
    desA[j++] = srcA[i];
    desA[j] = '\0';
  }

  for(int i = 0; i<sizeof desA; i++) //displaying contents of the new array
  {
    byte y = desA[i];
    if(y < 0x10)
    {
      Serial.print('0');
    }
    Serial.print(desA[i], HEX);
  }
}

void loop() {}

Output:

310032003300
6

Thanks

Instead of serial.print how can I make an array that i can use with with serial.write as hex(byte)

7

Did you see post #4, which does exactly what you asked?

8

Thanks, it has been a long time since i used Arduino and C,more than 10 years.
Will try it tomorrow , goodnight.

9

Given:

char srcA[] = {'1', '2', '3'};

What do you expect to see on Serial Monitor if the following code is executed:

Serial.write(srcA);
10

A somewhat cryptic method that relies upon the processor storing integers little-endian.

char srcA[] = "123";

void setup(){
  Serial.begin(9600);
  uint16_t dest[strlen(srcA)] = {0};
  for (size_t i = 0; i < strlen(srcA); i++){
    dest[i] = srcA[i];
  }
  Serial.println();
  Serial.write((byte*)dest, sizeof(dest));

  Serial.println();
  byte* b = (byte*)dest;
  for (size_t i = 0; i < sizeof(dest); i++){
    if (*b < 16) Serial.print('0');
    Serial.print(*b, HEX);
    b++;
    Serial.print(' ');
  }
}

void loop(){
}
11

Is the above declaration same as the following?

char srcA[] = {'1', '2', '3'};
12

Trick question :joy:

13

Roughly equivalent, the first adds a terminating null, so you can use strlen() to get the size instead of sizeof() for the 2nd, but after copying to the destination array I was using the output has no difference.

1 Like
14

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