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>       intInet_aton (Const Char*CP,structIn_addr *INP);//Convert the IP address of the point 4-segment to the structure IN_ADDR valuein_addr_t inet_addr (Const Char*CP);//Convert string to struct IN_ADDR valuein_addr_t Inet_network (Const Char*CP);//Convert the network part of the string address to the structure in_addr value       Char*inet_ntoa (structIn_addrinch);//Convert structure in_addr to string       structIN_ADDR inet_makeaddr (intNetintHost);//The network address and host address are synthesized as IP addresses, and the return value is in_addr valuein_addr_t inet_lnaof (structIn_addrinch);//Get the host part of the addressin_addr_t Inet_netof (structIn_addrinch);//Get the network portion of the address

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>intMainintARGC, 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[ -]; Char*str=null,*STR2=null;intErr =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 first192.168.1.1, in the test255.255.255.255 */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, test 192.168.1.1 First, test 255.255.255.255 * Proof function non-reentrant * /IP.S_ADDR =192<< -|168<< -|1<<8|1;    str = INET_NTOA (IP); IP.S_ADDR =255<< -|255<< -|255<<8|255; STR2 = Inet_ntoa (IP);printf("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);printf("inet_ntoa:string %s ip:0x%x \ n", STR,IP.S_ADDR);/ * Test function inet_lnaof, get native address * /Inet_aton (ADDR1, &AMP;IP);Local. s_addr = htonl (IP.S_ADDR);Local. s_addr = inet_lnaof (IP); str = INET_NTOA (Local);printf("inet_lnaof:string %s ip:0x%x \ n"StrLocal. s_addr);/ * Test function Inet_netof, get native address * /NETWORK.S_ADDR = Inet_netof (IP);printf("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 AddrlenintMainintargcChar*argv[]) {structIN_ADDR IP;Charipstr[]="192.168.1.1";/ * Network Address String * /    CharAddr[addrlen];/ * Save converted string IP address, 16 byte size * /    Const Char*str=null;intErr =0;/ * return value * /    / * Test function Inet_pton convert 192.168.1.1 to binary form * /Err = Inet_pton (Af_inet, Ipstr, &AMP;IP);/ * Convert 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<< -|168<< -| A<<8|255);/*192.168.12.255*/    / * Convert binary network byte order 192.168.12.255 to 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