Hex to char array in C

Question

Given a string of hex values i.e. e.g. \"0011223344\" so that\'s 0x00, 0x11 etc.

How do I add these values to a char array?

Equivalent to say:

<

Answer 1

Let's say this is a little-endian ascii platform. Maybe the OP meant "array of char" rather than "string".. We work with pairs of char and bit masking.. note shiftyness of x16..

/* not my original work, on stacko somewhere ? */

for (i=0;i < 4;i++) {

    char a = string[2 * i];
    char b = string[2 * i + 1];

    array[i] = (((encode(a) * 16) & 0xF0) + (encode(b) & 0x0F));
 }

and function encode() is defined...

unsigned char encode(char x) {     /* Function to encode a hex character */
/****************************************************************************
 * these offsets should all be decimal ..x validated for hex..              *
 ****************************************************************************/
    if (x >= '0' && x <= '9')         /* 0-9 is offset by hex 30 */
        return (x - 0x30);
    else if (x >= 'a' && x <= 'f')    /* a-f offset by hex 57 */
        return(x - 0x57);
    else if (x >= 'A' && x <= 'F')    /* A-F offset by hex 37 */
        return(x - 0x37);
}

This approach floats around elsewhere, it is not my original work, but it is old. Not liked by the purists because it is non-portable, but extension would be trivial.