Use the C language to determine if an IP address is a private address

Reference: https://zhidao.baidu.com/question/191740827.html

Private IP address range:
a:10.0.0.010.255.255.255 10.0.0.0/8
b:172.16.0.0172.31.255.255 172.16.0.0/12
c:192.168.0.0192.168.255.255 192.168.0.0/16

The socket structure in the C language is as follows

struct sockaddr_in {    short   sin_family;    USHORT  Sin_port;    IN_ADDR sin_addr;    CHAR sin_zero[8];}

Where the IP address field is SIN_ADDR, when you select an IP address of type IPV4, Sin_addr is a 4-byte number for a network byte order.

Sample
192.168.207.1
C0 A8 CF 01

Filter:
A:startwith 10.x.x.x
B:startwith 172. (16~31). x.x
C:startwith 192.168.x.x

Order of Judgment:

B, C, A

The pseudo code is as follows:

Char data[4] = networkaddr;

If data[0] = = 10:
return True
Elif Data[0] = = 192 and data[1] = = 168:
return True
Elif data[0] = = 172:
If data[1] >= and data[1] <= 31:
return True
Else
Return False

#include <Windows.h>#include<stdio.h>#include<string.h>#pragmaComment (lib, "Ws2_32.lib")//inet_addr ()BOOL islocaladdr (DWORD netaddr) {unsignedChardata[4]; BOOL BRet=FALSE; memcpy (data, (Char*) &netaddr,4); if(Ten= = data[0]) {BRet=TRUE; }    Else if(192= = data[0] &&168= = data[1]) {BRet=TRUE; }    Else if(172= = data[0])    {        if(data[1] >= -&& data[1] <= to) {BRet=TRUE; }    }    Else if(!MEMCMP (data, SERVADDR,4) ) {BRet=TRUE; }    returnBRet;}intMain () {Char*addrlist[] = {        "192.168.207.1",        "192.12.1.3",        "172.16.2.1",        "172.33.1.1",        "10.12.12.1",        "43.1.31.23",    }; Char*result[] = {        "X Local Address",        "O Local Address"    }; intaddrcnt =sizeof(addrlist)/sizeof(addrlist[0]); DWORD netaddr=0; BOOL ret=FALSE;  for(inti =0; i < addrcnt; i++) {netaddr=inet_addr (Addrlist[i]); RET=islocaladdr (NETADDR); printf ("%-16s [%s]\n", Addrlist[i], Result[ret]); }    return 0;}

Operation Result:

Use the C language to determine if an IP address is a private address