char to int: a twist

Guru3 · 12-04-2004, 12:19 PM

I've got two chars, say a and b. For example A is '2' and B is 'F'. How can I get the integer value of the hex those two make up, ie, 0x2F?

Pecunia · 12-04-2004, 12:51 PM

Something like this? (in C)

Code:

#include <ctype.h>

int hextoint(char c) {
	if (!isxdigit(c)) {
		return -1;
	}
	if (isdigit(c)) {
		return c - '0';
	}
	c = toupper(c);
	return c - 'A' + 0xA;
}

int do_funny_stuff(char a, char b) {
	int aa, bb;
	aa = hextoint(a);
	bb = hextoint(b);
	if (aa == -1 || bb == -1) {
		return -1;
	}
	return aa << 4 | bb;
}

itsme86 · 12-04-2004, 06:23 PM

Another way could be:

Code:

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
  char a = '2', b = 'f';
  char buf[3];
  int val;

  sprintf(buf, "%c%c", a, b);  // or buf[0] = a, buf[1] = b, buf[2] = 0;
  val = strtol(buf, NULL, 16);

  printf("%X\n", val);

  return 0;
}

Quote:

itsme@dreams:~/C$ ./getnum
2F

eantoranz · 12-04-2004, 08:35 PM

Maybe I'm plain wrong, but I THINK there are some ansi functions to handle hex conversions.

Guru3 · 12-05-2004, 03:05 AM

i found sscanf.

Code:

int d;
char[] s = "AF";
sscanf(s, "%x", &d);

works perfectly, and thank you for your replies

eantoranz · 12-05-2004, 08:49 AM

This is one of the few times I get proud of my memory!

You're welcome.