有幸找到IP分析源码。
这两天翻硬盘资料，找到windows 2000关于网络IP的一份源码。
看见网络上只有CSDN处有一份，于是贴了出来，含源码分析。
inet_addr函数_misterliwei的专栏-CSDN博客_inet_addr函数
/*++
Copyright (c) 1991 Microsoft Corporation
Module Name:
i_addr.c
Abstract:
This module implements a routine to convert internet address expressed
as dotted-decimal character strings into numerical representation.
Author:
Mike Massa (mikemas) Sept 20, 1991
Revision History:
Who When What
-------- -------- ----------------------------------------------
mikemas 9-20-91 created
Notes:
Exports:
inet_addr()
--*/
#ident "@(#)inet_addr.c 5.3 3/8/91"
/*
* Copyright (c) 1987, Spider Systems Limited
*/
/* inet_addr.c 1.0 */
/*
* /usr/projects/tcp/SCCS.rel3/rel/src/lib/net/0/s.inet_addr.c
* @(#)inet_addr.c 5.3
*
* Last delta created 14:10:41 3/4/91
* This file extracted 11:20:19 3/8/91
*
*/
/****************************************************************************/
#include "winsockp.h"
#include <ctype.h>
/*
* Internet address interpretation routine.
* All the network library routines call this
* routine to interpret entries in the data bases
* which are expected to be an address.
* The value returned is in network order.
*/
unsigned long PASCAL
inet_addr(
IN const char *cp
)
/*++
Routine Description:
This function interprets the character string specified by the cp
parameter. This string represents a numeric Internet address
expressed in the Internet standard ".'' notation. The value
returned is a number suitable for use as an Internet address. All
Internet addresses are returned in network order (bytes ordered from
left to right).
Internet Addresses
Values specified using the "." notation take one of the following
forms:
a.b.c.d a.b.c a.b a
When four parts are specified, each is interpreted as a byte of data
and assigned, from left to right, to the four bytes of an Internet
address. Note that when an Internet address is viewed as a 32-bit
integer quantity on the Intel architecture, the bytes referred to
above appear as "d.c.b.a''. That is, the bytes on an Intel
processor are ordered from right to left.
Note: The following notations are only used by Berkeley, and nowhere
else on the Internet. In the interests of compatibility with their
software, they are supported as specified.
When a three part address is specified, the last part is interpreted
as a 16-bit quantity and placed in the right most two bytes of the
network address. This makes the three part address format
convenient for specifying Class B network addresses as
"128.net.host''.
When a two part address is specified, the last part is interpreted
as a 24-bit quantity and placed in the right most three bytes of the
network address. This makes the two part address format convenient
for specifying Class A network addresses as "net.host''.
When only one part is given, the value is stored directly in the
network address without any byte rearrangement.
Arguments:
cp - A character string representing a number expressed in the
Internet standard "." notation.
Return Value:
If no error occurs, inet_addr() returns an in_addr structure
containing a suitable binary representation of the Internet address
given. Otherwise, it returns the value INADDR_NONE.
--*/
{
register unsigned long val, base, n;
register char c;
unsigned long parts[4], *pp = parts;
WS_ENTER( "inet_addr", (PVOID)cp, NULL, NULL, NULL );
again:
/*
* Collect number up to ``.''.
* Values are specified as for C:
* 0x=hex, 0=octal, other=decimal.
*/
val = 0; base = 10;
if (*cp == '0') {
base = 8, cp++;
if (*cp == 'x' || *cp == 'X')
base = 16, cp++;
}
while (c = *cp) {
if (isdigit(c)) {
val = (val * base) + (c - '0');
cp++;
continue;
}
if (base == 16 && 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)
*/
/* GSS - next line was corrected on 8/5/89, was 'parts + 4' */
if (pp >= parts + 3) {
WS_EXIT( "inet_addr", -1, TRUE );
return ((unsigned long) -1);
}
*pp++ = val, cp++;
goto again;
}
/*
* Check for trailing characters.
*/
if (*cp && !isspace(*cp)) {
WS_EXIT( "inet_addr", -1, TRUE );
return (INADDR_NONE);
}
*pp++ = val;
/*
* Concoct the address according to
* the number of parts specified.
*/
n = (unsigned long)(pp - parts);
switch ((int) n) {
case 1: /* a -- 32 bits */
val = parts[0];
break;
case 2: /* a.b -- 8.24 bits */
if ((parts[0] > 0xff) || (parts[1] > 0xffffff)) {
WS_EXIT( "inet_addr", -1, TRUE );
return(INADDR_NONE);
}
val = (parts[0] << 24) | (parts[1] & 0xffffff);
break;
case 3: /* a.b.c -- 8.8.16 bits */
if ((parts[0] > 0xff) || (parts[1] > 0xff) ||
(parts[2] > 0xffff)) {
WS_EXIT( "inet_addr", -1, TRUE );
return(INADDR_NONE);
}
val = (parts[0] << 24) | ((parts[1] & 0xff) << 16) |
(parts[2] & 0xffff);
break;
case 4: /* a.b.c.d -- 8.8.8.8 bits */
if ((parts[0] > 0xff) || (parts[1] > 0xff) ||
(parts[2] > 0xff) || (parts[3] > 0xff)) {
WS_EXIT( "inet_addr", -1, TRUE );
return(INADDR_NONE);
}
val = (parts[0] << 24) | ((parts[1] & 0xff) << 16) |
((parts[2] & 0xff) << 8) | (parts[3] & 0xff);
break;
default:
WS_EXIT( "inet_addr", -1, TRUE );
return (INADDR_NONE);
}
val = htonl(val);
WS_EXIT( "inet_addr", val, FALSE );
return (val);
}源码分析，这个程序模块是解析IP地址的。内容有优化过。
cp这个变量指针指向IP地址，一字节一字节的分析IP地址。
这模块文件头注释有说明：
IP 地址输入有几种方式： a.b.c.d 方式 a b c d 是8位bit。
a.b.c 方式 a b 是8 位bit c 是16位bit。
a.b 方式 a 是8位bit b是24位bit
程序是判断字符型地址的如 127.0.0.1 这个方式的字符地址。
也可以输入地址的8进制 020
也可以输入0x50 16进制
然后可以按 a.b.c 的方式组合输入试试
这是windos 2000 IP地址的表示方式。现在有没限止不太清楚，自己可以试一下。
还有个 val= htonl(val); 这好像就是内码吧。
不知道大家看懂没。
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