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Hector Seguro
Asked: 2020-06-17 18:53:41 +0800 CST 2020-06-17 18:53:41 +0800 CST

Convert char array to a byte

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    void loop() {
      String str = "F03A42";
      int start = 0;
      int arr[2][19];
      int t = 0;
      //El 'for' lo hace 6 veces hasta que acaba la cadena de datos
      for(int ends = 2;ends <= sizeof(str); ends += 2){
        char s[2];
        //Extra los 2 caracteres necesarios para la conversion
        str.substring(start, ends).toCharArray(s, sizeof(s) + 1);
        //Luego lo pasa a un array para luego procesarlo de otra manera
        //Aqui el problema, si hago:
        //arr[t] = (int)s & 0xFF; da un numero estatico (242)
        arr[t] = s; 
        start += 2;
        t++;
      }
   }

Example: F0 is written in hex (supposedly) but I need to pass that 2 char to a full-fledged byte.

void simplificado(){
    //El byte
    char bit[2] = 'F0';
    //Ejemplo
    byte d = CharToByte(bit);
    //Pero que si convierto 'd' se igual a 240 (Que es el numero entero de 0xF0)
}
c

2 Answers

  1. Best Answer

    You can use sscanf, but for something this simple it may be convenient (efficiency) to program it yourself. For example (using plain C strings)

    #include<stdio.h>
// convierte un caracter hexa al valor entero. 
int parseHexaChar(char A) {
    return (A > '9')? (A &~ 0x20) - 'A' + 10: (A - '0');
}

int main(void)
{
      char str[] = "F03A42";
      int bytes =  sizeof(str)/2; // cuidado: habría que asegurarse que el string tenga largo par
      char *p = &str[0];
      int i;
      for( i=0; i< bytes;i++) {
            int val = parseHexaChar(*p++)*16 + parseHexaChar(*p++);
            printf("%d\n",val);
      }
}
    • 1

  2. leonbloy 's answer is correct but does not have to be valid for all platforms since not all character tables have all contiguous letters and numbers (like IBM's infamous EBCDIC ); Despite this, the code in your answer would work in many cases (even with many versions of EBCDIC), but to be on the safe side, I would like to propose an approach based on switch:

    int char_to_int(char c)
{
    switch (c)
    {
        case '0': return 0;
        case '1': return 1;
        case '2': return 2;
        case '3': return 3;
        case '4': return 4;
        case '5': return 5;
        case '6': return 6;
        case '7': return 7;
        case '8': return 8;
        case '9': return 9;
        case 'a': case 'A': return 0xA;
        case 'b': case 'B': return 0xB;
        case 'c': case 'C': return 0xC;
        case 'd': case 'D': return 0xD;
        case 'e': case 'E': return 0xE;
        case 'f': case 'F': return 0xF;
        default:
            printf("Error '%c' no valido", c);
            exit(-1);
    }

    return 0;
}

    This swtichworks for any encoding, whether the letters and numbers are contiguous or not, for the conversion this simple function would suffice:

    int hex_to_int(char *hex, int length)
{
    int result = 0;

    for (char *c = hex, *e = c + length; c != e; ++c, --length)
    {
        result |= (char_to_int(*c) << ((length - 1) * 4));
    }

    return result;
}

    And it can be used like this:

    int main()
{
    char fabada[] = "fabada";
    char cafe[]   = "cafe";
    char baboso[] = "bab050";

    printf("fabada: %d\n", 0xfabada);
    printf("fabada: %d\n", hex_to_int(fabada, 6));

    printf("cafe: %d\n", 0xcafe);
    printf("cafe: %d\n", hex_to_int(cafe, 4));

    printf("bab050: %d\n", 0xbab050);
    printf("bab050: %d\n", hex_to_int(baboso, 6));

    return 0;
}

    The code can be seen working [here] and the output is as follows:

    fabada: 16431834
fabada: 16431834
cafe: 51966
cafe: 51966
bab050: 12234832
bab050: 12234832
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