Thread: No atoh() function in C ( Ascii To Hex )? - Well, Let's Create One

I can't argue that this is simpler than what's already been suggested, but it's probably faster with larger strings:

Code:

char *
atohx(char * dst, const char * src)
{	
	char 
		* ret = dst;
	for(int lsb, msb; *src; src += 2)
	{	
		msb = tolower(*src);
		lsb = tolower(*(src + 1));
		msb -= isdigit(msb) ? 0x30 : 0x57;
		lsb -= isdigit(lsb) ? 0x30 : 0x57;
		if((msb < 0x0 || msb > 0xf) || (lsb < 0x0 || lsb > 0xf))
		{
			*ret = 0;
			return NULL;
		}
		*dst++ = (char)(lsb | (msb << 4));  
	}
	*dst = 0;
	return ret;
}