Linux Network Programming--string IP and binary IP conversion

One: unsafe (non-reentrant) inet_xxx () function Family

Since computer-understood IP is stored in binary form, the conversion of string IP and binary IP is often required in network programming, and the Linux system has a set of functions to be used for network address translation, as follows:

       #include <sys/socket.h>       #include <netinet/in.h>       #include <arpa/inet.h>       int Inet_aton (const char *CP, struct in_addr *inp);//Convert the DOT 4-segment IP address to the structure in_addr value       in_addr_t inet_addr (const char *CP);//convert string to structure in _addr value       in_addr_t inet_network (const char *CP);//Convert the network portion of the string address to the struct in_addr value       char *inet_ntoa (struct in_addr in) ;//Convert structure in_addr to string       struct in_addr inet_makeaddr (int net, int host)//combine network address and host address into IP address, return value is in_addr value       in_addr _t inet_lnaof (struct in_addr in);//Get the host part of the address       in_addr_t inet_netof (struct in_addr in);//Get the address of the network part

some of the above functions are defective, for example:

The Inet_ntoa function return value is a pointer to a string, this memory will be overwritten every time the Inet_nota function is called, if you do not take the data in time, there will be unexpected errors, so the function is unsafe, there is a hidden danger;

The return value of the Inet_addr,inet_network function is 1 when it represents an error, occupies the value of address 255.255.255.255, there is a flaw, buried the hidden trouble.

Here's a piece of code that shows you how to use and what's hidden:

#include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <stdio.h># Include <string.h>int main (int argc, char *argv[]) {struct in_addr ip,local,network;char addr1[]= "192.168.1.1";/* Network address string */char addr2[]= "255.255.255.255"; char addr3[]= "192.16.1"; char addr[16];char *str=null,*str2=null;int err = 0;/ * Test function Inet_aton */err = Inet_aton (ADDR1, &AMP;IP); if (err) {printf ("inet_aton:string%s value is:0x%x\n", ADDR1, Ip.s_addr );} else{printf ("inet_aton:string%s error\n", ADDR1);} /* inet_addr, Test 192.168.1.1 First, test 255.255.255.255 */ip.s_addr = inet_addr (ADDR1), if (err! =-1) {printf ("inet_addr:string %s Value is:0x%x\n ", ADDR1, ip.s_addr);} else{printf ("inet_addr:string%s error\n", ADDR1);}; IP.S_ADDR = inet_addr (ADDR2), if (ip.s_addr! =-1) {printf ("inet_addr:string%s value is:0x%x\n", ADDR2, ip.s_addr);} else{printf ("inet_addr:string%s error\n", ADDR2);};/ * Inet_ntoa, first Test 192.168.1.1, test 255.255.255.255* proof function non-reentrant */ip.s_addr = 192<<24|168<<16|1<<8| 1;STR = Inet_ntoa (IP), ip.s_addr = 255&LT;&LT;24|255&LT;&LT;16|255&LT;&LT;8|255;STR2 = Inet_ntoa (IP);p rintf ("inet_ ntoa:ip:0x%x string1%s,pre is:%s \ n ", ip.s_addr,str2,str);/* Test function inet_addr */ip.s_addr = inet_addr (ADDR3); if (err! =-1) { printf ("inet_addr:string%s value is:0x%x\n", ADDR3, ip.s_addr);} else{printf ("inet_addr:string%s error\n", ADDR3);}; str = INET_NTOA (IP);p rintf ("inet_ntoa:string%s ip:0x%x \ n", str,ip.s_addr);/* Test function inet_lnaof, get the native address */inet_aton (ADDR1 , &ip); local.s_addr = htonl (ip.s_addr); local.s_addr = inet_lnaof (IP); str = inet_ntoa (local);p rintf ("Inet_lnaof: String%s ip:0x%x \ n ", str,local.s_addr);/* Test function Inet_netof, get the native address */network.s_addr = Inet_netof (IP);p rintf (" Inet_netof : value:0x%x \ n ", network.s_addr); return 0;}

Operation Result:

two. Secure Address conversion function Inet_pton (), Inet_ntop ()the function Inet_pton (), Inet_ntop (), is reentrant and supports multiple address types, including IPV4 and IPV6.

Function Description:

Here's a piece of code to explain how to use it:

#include <sys/types.h> #include <sys/socket.h> #include <arpa/inet.h> #include <stdio.h># Include <string.h> #define Addrlen 16int Main (int argc, char *argv[]) {struct in_addr ip;char ipstr[]= "192.168.1.1" ; */* Network address string */char addr[addrlen];/* Save converted string IP address, 16 byte size */const char*str=null;int err = 0;/* return value *//* Test function Inet_pton Conversion 192 .168.1.1 is in binary form */err = Inet_pton (Af_inet, Ipstr, &IP);/* Converts a string to binary */if (Err > 0) {printf ("inet_pton:ip,%s value is : 0x%x\n ", ipstr,ip.s_addr);} /* Test function Inet_ntop convert 192.168.1.1 to String */ip.s_addr = Htonl (192<<24|168<<16|12<<8|255);/* 192.168.12.255*//* converts a binary network byte order 192.168.12.255 to a string */str = (const char*) inet_ntop (Af_inet, (void*) &ip, (char*) & Addr[0], Addrlen); if (str) {printf ("inet_ntop:ip,0x%x is%s\n", ip.s_addr,str);} return 0;}

Operation Result:

inet_pton:ip,192.168.1.1 value IS:0X101A8C0
INET_NTOP:IP,0XFF0CA8C0 is 192.168.12.255

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

Linux Network Programming--string IP and binary IP conversion