Linux网络编程——inet_addr()函数源代码

https://opensource.apple.com/source/Libc/Libc-166/net.subproj/inet_addr.c.auto.html

/*
 * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
 */

#include 
#include 
#include 
#include 

/*
 * Ascii internet address interpretation routine.
 * The value returned is in network order.
 */
u_long inet_addr(cp)
	register const char *cp;	//K&C老式的函数定义方法，不提倡使用了
{
	struct in_addr val;

	if (inet_aton(cp, &val))
		return (val.s_addr);
	return (INADDR_NONE);
}

/* 
 * Check whether "cp" is a valid ascii representation
 * of an Internet address and convert to a binary address.
 * Returns 1 if the address is valid, 0 if not.
 * This replaces inet_addr, the return value from which
 * cannot distinguish between failure and a local broadcast address.
 */
int
inet_aton(cp, addr)
	register const char *cp;
	struct in_addr *addr;
{
	register u_long val;
	register int base, n;
	register char c;
	u_int parts[4];
	register u_int *pp = parts;

	for (;;) {
		/*
		 * Collect number up to ``.''.
		 * Values are specified as for C:
		 * 0x=hex, 0=octal, other=decimal.
		 */
		val = 0; base = 10;
		if (*cp == '0') {
			if (*++cp == 'x' || *cp == 'X')
				base = 16, cp++;
			else
				base = 8;
		}
		while ((c = *cp) != '\0') {
			if (isascii(c) && isdigit(c)) {
				val = (val * base) + (c - '0');
				cp++;
				continue;
			}
			if (base == 16 && isascii(c) && isxdigit(c)) {
				val = (val << 4) + 
					(c + 10 - (islower(c) ? 'a' : 'A'));
				cp++;
				continue;
			}
			break;
		}
		if (*cp == '.') {
			/*
			 * Internet format:
			 *	a.b.c.d
			 *	a.b.c	(with c treated as 16-bits)
			 *	a.b	(with b treated as 24 bits)
			 */
			if (pp >= parts + 3 || val > 0xff)
				return (0);
			*pp++ = val, cp++;
		} else
			break;
	}
	/*
	 * Check for trailing characters.
	 */
	if (*cp && (!isascii(*cp) || !isspace(*cp)))
		return (0);
	/*
	 * Concoct the address according to
	 * the number of parts specified.
	 */
	n = pp - parts + 1;
	switch (n) {

	case 1:				/* a -- 32 bits */
		break;

	case 2:				/* a.b -- 8.24 bits */
		if (val > 0xffffff)
			return (0);
		val |= parts[0] << 24;
		break;

	case 3:				/* a.b.c -- 8.8.16 bits */
		if (val > 0xffff)
			return (0);
		val |= (parts[0] << 24) | (parts[1] << 16);
		break;

	case 4:				/* a.b.c.d -- 8.8.8.8 bits */
		if (val > 0xff)
			return (0);
		val |= (parts[0] << 24) | (parts[1] << 16) | (parts[2] << 8);
		break;
	}
	if (addr)
		addr->s_addr = htonl(val);
	return (1);
}